Black Sigatoka, an Important Disease of Banana Black Sigatoka of Banana: The most important disease of a most important fruit Ploetz, R.C. 2001. Black Sigatoka of Banana. The Plant Health Instructor. DOI: 10.1094/PHI-I-2001-0126-02. Tropical Research and Education Center, University of Florida, IFAS, Homestead Origins and importance of banana as a food crop Banana is one of the most fascinating and important of all crops. It is a large monocotyledenous herb that originated in Southeast Asia. Virtually all of the cultivars that are grown are thought to have been selected as naturally occurring hybrids in this region by the earliest of farmers. In fact, Norman Simmonds proposed that banana was one of the first crops to be domesticated by man. In writing of the beginnings of agriculture in Southeast Asia, he concluded, "It seems a reasonable assumption that the bananas evolved along with the earliest settled agriculture of that area and may therefore be some tens of thousands of years old." Despite the current, clear understanding of its ancestry, the edible bananas' origins are often confused in the literature.

Almost all of the 300 or more cultivars that are known arose from two seeded, diploid species, Musa acuminata Colla and M. balbisiana Colla; they are diploid, triploid and tetraploid hybrids among subspecies of M. acuminata, and between M. acuminata and M. balbisiana. Conventionally, the haploid contributions of the respective species to the cultivars are noted with an A and B. For example, the Cavendish cultivars that are the mainstays of the export trades are pure triploid acuminata and, thus, AAA. The Linnaean species M. paradisiaca (the AAB plantains) and M. sapientum (the sweet dessert bananas, of which Silk AAB is the type cultivar) are invalid and no longer used. Women selling fruit of Dwarf Cavendish AAA and Pisang awak ABB in a market in Karonga, Malawi, East Africa. The lower photograph shows preparation of male buds of Pisang awak for cooking in a market in Sungai Kolok, Thailand. For many of the world’s poorest people, banana is a nutritious and important staple food.

Banana is now one of the most popular of all fruits. Although it is viewed as only a dessert or an addition to breakfast cereal in most developed countries, it is actually a very important agricultural product. After rice, wheat and milk, it is the fourth most valuable food. In export, it ranks fourth among all agricultural commodities and is the most significant of all fruits, with world trade totaling $2.5 billion annually. Yet, only 10% of the annual global output of 86 million tons enters international commerce. Much of the remaining harvest is consumed by poor subsistence farmers in tropical Africa, America and Asia. For most of the latter producers, banana and plantain (which is a type of banana) are staple foods that represent major dietary sources of carbohydrates, fiber, vitamins A, B6 and C, and potassium, phosphorus and calcium. This photograph shows seed-packed fruit of Musa balbisiana, one of the ancestors of the edible bananas. Since the edible cultivars are parthenocarpic and often female or male sterile, seeds are rarely found in their fruit. The latter factors, however, have made it difficult to improve this crop by breeding. Click image to enlarge.

Impact of banana diseases Diseases are among the most important factors in banana production worldwide. They are the reasons for which all of the world’s breeding programs were created and remain a primary focus of all current programs. Recently, diseases also became principal targets of biotechnological efforts to improve this crop and ). A leaf spot disease is the most important of these problems. Black Sigatoka, which is also known as black leaf streak, causes significant reductions in leaf area, yield losses of 50% or more, and premature ripening, a serious defect in exported fruit. It is more damaging and difficult to control than the related yellow Sigatoka disease, and has a wider host range that includes the plantains and dessert and ABB cooking bananas that are usually not affected by yellow Sigatoka. A close-up of the adaxial surface of a banana leaf that is affected by black Sigatoka. Under high rainfall and humidity, these lesions will coalesce and kill the entire leaf. Click image for enlargement. Damage caused by black Sigatoka in a planting of Dwarf Cavendish AAA in Malawi, East Africa. Note the scarcity of healthy leaf tissue on plants that carry fruit.

Yields from such plants are usually a half or less than that from healthy plants. Click image for enlargement. In export plantations, Black Sigatoka is controlled with frequent applications of fungicides and cultural practices, such as the removal of affected leaves, and adequate spacing of plants and efficient drainage within plantation. In total, these are very expensive practices. For example, fungicide application includes the use of airplanes or helicopters, permanent landing strips and facilities for mixing and loading the fungicides, and the high recurring expense of the spray materials themselves. In total, it has been estimated that the costs of control are ultimately responsible for 15-20% of the final retail price of these fruit in the importing countries. Their great expense makes them essentially unavailable to small-holder farmers who grow this crop, it is these producers who are affected most by this important disease. Aerial application of fungicides to control black Sigatoka in Honduras. In the final analysis, the costs associated with these control measures are directly responsible for 15-20% of the purchase price of exported fruit in the importing countries. (Photo courtesy of R.H. Stover).

Distribution, etiology and epidemiology of black Sigatoka Black Sigatoka was first recognized in the Sigatoka Valley of Fiji in 1963, but was probably widespread in Southeast Asia and the South Pacific by that time. In the Western Hemisphere, it first appeared in 1972 in Honduras and now occurs on the mainland from central Mexico south to Bolivia and northwestern Brazil, and in the Caribbean basin in Cuba, Jamaica, the Dominican Republic and southern Florida. In Africa, the disease was first recorded in Zambia in 1973 and has since spread throughout the sub-Saharan portions of that continent. In most areas, black Sigatoka has now replaced yellow Sigatoka to become the predominant leaf spot disease of banana. Black Sigatoka is caused by the ascomycete, Mycosphaerella fijiensis Morelet [anamorph: Paracercospora fijiensis (Morelet) Deighton] (a variant of the pathogen, M. fijiensis var. difformis, that was previously reported in tropical America, is no longer recognized). The pathogen produces conidia and ascospores, both of which are infective.

They are formed under high moisture conditions, and are disseminated by wind, and in the case of conidia, also by rain and irrigation water. Due to their greater abundance and small size, ascospores are more important than conidia in spreading the disease within plants and plantations. In contrast, infected planting material and leaves, which are used often in the developing world as packing materials, are usually responsible for the long-distance spread of the disease. The recent outbreak of black Sigatoka in South Florida almost certainly resulted from the importation of infected germplasm by local growers (see Plant Disease note D-1998-1217-03N) . "Damn, how did this get here?" Dr. Jonathan Crane, Extension Tropical Fruit Crops Specialist for the University of Florida in Homestead, examines a leaf of the banana cultivar Rajapuri AAB that is affected by black Sigatoka. The importation of infected propagation material, which is a common and effective means for moving this disease long distances, was probably responsible for the recent outbreak of black Sigatoka in South Florida. Control Chemical control of first yellow, and then black, Sigatoka has evolved considerably over the last 65 years.

Bordeaux mixture, first used in the mid-1930s, has been replaced by several succeeding generations of protectant and, later, systemic fungicides. Presently, a sterol biosynthesis inhibitor, tridemorph, several different sterol demethylation inhibitors, most importantly propiconazole, and the methoxyacrylate, azoxystrobin, are the most commonly used systemics. Since there is a tendency for resistance or tolerance to develop in M. fijiensis towards the systemic fungicides, they are usually applied in combination or alternation with broad-spectrum, protectant fungicides, such as the dithiocarbamates and chlorothalonil. With the exception of chlorothalonil, these fungicides are usually mixed with petroleum-based spray oils. The oils themselves are fungistatic and retard the development of the pathogen in the infected leaf. When they are mixed in water emulsions with fungicides, the resulting “cocktails” provide superior disease control. The export plantations in the Philippines and Central and South America that produce fruit for the developed world are vast monocultures of Cavendish cultivars, usually of Grand Nain but also of Williams and Valery.

In order to treat these large areas with fungicides, helicopters or fixed wing aircraft are used. Application schedules in the plantations are routinely determined with disease-forecast systems that incorporate data on disease severity within the plantation and environmental factors that are known to affect infection and disease development. These epidemiological tools enabled producers in Central America to substantially reduce the number of fungicide applications that were needed for control. However, increased tolerance in the pathogen to the DMI fungicides has made it necessary to increase applications in several countries in the region to previous frequencies of 25 - 40 per year. Aerial view of an export plantation of the Cavendish cultivar Grand Nain in the Sula Valley of Honduras. Such vast monocultures allow fruit to be produced efficiently, but require that fungicides for black Sigatoka control be applied by aircraft. The annual cost of fungicide applications in export plantations is about $1,000 per hectare. Although the international trades can add this expense to the price they charge for fruit, this is not an option for subsistence farmers. Thus, the latter producers must use different strategies to manage black Sigatoka.

These include the removal of older leaves to reduce inoculum levels in a plantation, interplanting with other nonsusceptible crops, and planting in partial shade which results in less severe disease development. The potential for bred bananas Given the high expense of fungicides, their unavailability for subsistence farmers, and the recurring problem with fungicide resistance in the export plantations, it is clear that genetic resistance to black Sigatoka would be most useful. If resistant, agronomically acceptable cultivars were available, they would provide the best solution to this problem in export and subsistence situations alike. Unfortunately, resistance to black Sigatoka among pre-existing banana genotypes is poor. The Cavendish cultivars that are used for export are so susceptible that nothing short of intensive fungicide application will control the disease in most areas. Resistant cultivars that could be used in subsistence situations are available, but they are usually less productive or desirable than those that are susceptible. This situation has begun to change as a result of new, resistant hybrids that are being developed by the banana breeding programs ( ).

The first program to make significant progress in improving this crop was that of the Fundación Hondureña de Investigación Agrícola (FHIA ) in La Lima, Honduras. It was begun by the United Fruit Company (now Chiquita Brands ) in 1959, but was donated to this private agricultural research foundation in 1984. FHIA has developed numerous dessert, plantain and cooking hybrids, several of which have been tested in the International Musa Testing Programme of the International Network for the Improvement of Banana and Plantain ( ). Results from these and other trials indicate that the FHIA clones are generally very vigorous and produce high yields under a wide range of environmental and edaphic conditions. Importantly, they resist pathogenically and geographically diverse populations of M. fijiensis, as well as two other major problems, Panama disease, (fusarium wilt) and nematodes. Unfortunately, since they do not yet meet the high standards of the export trades, they have only been adopted for local consumption in East Africa, tropical America and the Caribbean. In the future, products of the breeding programs will play increasingly important roles in subsistence agriculture.

Whether new hybrids are used eventually to replace the Cavendish cultivars that are used by the export trades, however, remains to be seen. The very substantial infrastructure that characterizes export production is focussed on producing only these cultivars. Converting these operations to the production and handling of another type of banana would be an expensive proposition. Moreover, the currently available hybrids do not meet the very high standards for fruit quality and post-harvest shelflife that are demanded by the trades. Yet, as fungicides continue to lose their effectiveness against black Sigatoka, and as the practice of fungicidal disease control becomes more expensive and less appealing to consumers in the importing countries, the trades may eventually be forced into making the difficult transition away from the Cavendish clones. References 1. Carlier, J., X. Mourichon, D. Gonzâlez de León, M.F. Zapater, and M.H Lebrun. 1994. DNA restriction fragment length polymorphisms in Mycosphaerella species that cause banana leaf spot diseases. Phytopathology 84:751-756. 2. Carreel, F., S. Fauré, D.

Gonzâlez de León, P.J.L. Lagoda, X. Perrier, F. Bakry, H. Tezenas du Montcel, C. Lanaud, and J.P. Horry. 1994. Évaluation de la diversité génétique chez les bananiers diploïdes (Musa spp.). Genet. Sel. Evol. 26:125s-136s. 3. Fullerton, R.A., and R.H. Stover (eds.). 1990. Sigatoka Leaf Spot Diseases of Banana: Proceedings of an International Workshop held at San José, Costa Rica, 28 March – 1 April, 1989. INIBAP. Montpellier, France. 374 pp. 4. Gauhl, F. 1994. Epidemiology and Ecology of Black Sigatoka (Mycosphaerella fijiensis Morlet) on Plantain and Banana (Musa spp.) in Costa Rica, Central America. Ph.D. dissertation, Universität Göttingen, 1989.

(translated to English from German by INIBAP, Montpellier, France). 120 pp. 5. International Network for the Improvement of Banana and Plantain. 1994. Annual Report, 1993. Montpellier, France. 73 pp. 6. Kress, W.J. 1990. The phylogeny and classification of the Zingiberales. Annals of the Missouri Botanical Garden 77:698-721. 7. Mourichon, X., J. Carlier, and Fouré. 1997. Sigatoka leaf spot diseases. Musa Disease Fact Sheet No. 8. INIBAP, Montpellier, France. 4 pp. 8. Ortiz, R. 1995. Musa genetics. In: Gowen, S. (ed.) Bananas and Plantains. Chapman & Hall. London. pp. 84-109 9. Ploetz, R.C., and X. Mourichon. 1999. First report of black Sigatoka in Florida. (Disease Note) Plant Disease 83:300. 10.

Rhodes, P.L. 1964. A new banana disease in Fiji. Commonwealth Phytopathological News 10:38-41. 11. Simmonds, N.W. and K. Shepherd. 1955. Taxonomy and origins of cultivated bananas. Journal of the Linneaen Society of Botany (London) 55:302-312. 12. Simmonds, N.W. 1966. Bananas. 2nd edition. Longmans. London. 512 pp. 13. Stover, R.H. 1980. Sigatoka leaf spot diseases of bananas and plantains. Plant Disease 64:750-756. Banana - Black Sigatoka Disease | Horticulture and Home Pest News Banana - Black Sigatoka Disease This article was published originally on 3/23/2005 Byline: by Paula Flynn, Department of Plant Pathology Banana is a popular fruit. It's easy to peel, easy to eat, and easy to find, typically located in a prominent spot in the produce section of a grocery store.

With the wheels of the grocery cart still moving, we don't stop to think about the battles the banana grower had to fight to provide a perfect fruit for our convenient consumption. Black Sigatoka is a leaf spot disease of banana that can cut a tree's fruit production in half. The fungal disease causes dark leaf spots that eventually enlarge and coalesce, causing much of the leaf area to turn yellow and brown. The high rainfall and humidity of the tropical regions in which bananas are grown are especially favorable for disease development. The fungus that causes black Sigatoka, Mycosphaerella fijiensis, is spread from tree to tree by wind, rain, and irrigation water. The name black Sigatoka was given to the disease because it was first discovered in 1963 in the Sigatoka Valley of Fiji. Black Sigatoka is a difficult and expensive disease to control. It is estimated that 15-20% of the price of bananas is due to the cost of the disease control measures that are used to produce the fruit. Airplanes or helicopters are used to apply fungicides to leaves.

Cultural practices such as removing diseased leaves and pruning branches to improve air circulation are also helpful in reducing the occurrence of the disease, but these practices are labor intensive. Because fungicides are used so frequently, growers are finding that the fungus is becoming resistant to the fungicide products applied to the crop. In addition, many of the farmers that operate small plantations cannot afford to purchase fungicides. A convenient and low-cost way to control the disease would be to grow banana varieties that are resistant to the disease, but the most popular banana cultivars grown are extremely susceptible to black Sigatoka. Fortunately, banana hybrids that show resistance to this disease are being developed. More work still needs to be done to identify hybrids that produce fruit with a good shelf life and that are acceptable in taste to the consumer. The next time a bright banana is grabbed from the countertop, remember that it took a diligent effort to provide it to you. Browning and yellowing of a banana leaf caused by the fungal disease, black Sigatoka. (Image taken in Costa Rica .) This article originally appeared in the 3/23/2005 issue.

Year of Publication: Black leaf streak | News, knowledge and information on bananas Distribution Pan-tropical Black leaf streak disease (BLSD), which is commonly known as black Sigatoka, is a leaf spot disease caused by the fungus Mycosphaerella fijiensis . The disease does not immediately kill banana plants, but by interfering with photosynthesis it can negatively impact bunch weight. Under favourable conditions for the fungus, and without chemical control, no functional leaf might be left at harvest and as a result yields can be reduced by 35 to 50%. BLSD also shortens the fruit's green life, the time between harvest and ripening. Fruits harvested from heavily infected plants ripen prematurely and unevenly, and as a result become unsuitable for export. The need to control the fungus to a level that does not affect the export of the fruit makes it the most economically important leaf disease of banana. High levels of BLSD severity have also been shown to increase susceptibility to crown rot disease [1] . Contents References Distribution The disease has been reported in most countries is which banana is grown. It was first reported in 1963, in Fiji's Sigatoka valley, after which black Sigatoka gets its name.

The fungus that causes the disease is however believed to have been widespread in the Asia-Pacific region long before then [2] . There are indications that it might have been in Taiwam as early as 1927 [2] . The earliest report of BLSD in Africa is from Zambia in 1973 [3] . However, the fungus could not identified and there is still no official confirmation of the disease in Zambia. The first authenticated report is from Gabon in 1980. The first record of BLSD in Latin America is from Honduras in 1972 [4] . The disease was first observed in Florida in 1998 [5] . Symptoms Most infections start on the underside of the leaf during the unfurling of the cigar leaf . The symptoms start as small specks that become streaks running parallel to the leaf veins. These streaks aggregate and eventually form spots that coalesce, form a chlorotic halo, and eventually merge to cause extensive necrosis. The first symptom, chlorotic specks, appears 14 to 20 days after infection.

The period between the specks and the appearance of streaks, and eventually necrotic spots, varies according to the cultivar and the severity of infection. Stages of development The first detailed description of symptoms into six stages was done by Meredith and Lawrence in 1969 [6] . The six stages were redefined by Eric Fouré in 1987 [7] . (Photos by R. Le Guen, CIRAD ) Stage 1 appears as yellowish specks that are less than 1 mm visible only on the underside of the leaf. This stage precedes stage 1 of Meredith and Lawrence of rusty-brown specks less than 0.25 mm in diameter on the underside of the leaf. Stage 2 appears as red or brown streaks on the underside of the leaf, and later on on the upper side of the leaf. The colour of the streak will change progressively to black on the upper side of the leaf. Stage 3 differs from the previous one by the dimensions of the streaks, which become longer and larger. Stage 4 appears as a brown spot on the underside of the leaf and as a black spot on the upper side. The spot takes an elliptical or circular form.

Stage 5 is the first of two necrotic stages. The spot is totally black and has spread to the underside of the leaf blade. It is surrounded by a yellow halo. Stage 6 is when the centre of the spot dries out, turns light gray and is surrounded by a well-defined black ring, which is itself surrounded by a bright yellow halo. Since the ring persists, these spots remain visible after the leaf has dried out. Disease parameters Youngest leaf spotted The youngest leaf spotted (YLS) is the youngest leaf with at least 10 necrotic lesions, according to the method developed by Stover [8] ; with counting done from the last leave to emerge, number 1. Monitoring the evolution of this parameter from the establishment of a plot of 10 homogenous plants to their flowering (and replacing them with 10 new plants before flowering) can be used to evaluate the effectiveness of a chemical control strategy [9] . If none of the leaves on a given plant have necrotic lesions, the value of YLS is N+1, where N is the number of functional leaves.

If the YLS decreases over time, the chemical control strategy is failing because it means that the formation of necrotic lesions is faster than the rate at which new leaves are emitted. An increasing YLS suggests that the chemical strategy is effective in slowing down the formation of necrotic lesions. Management The management of BLSD aims at conserving a minimum number of functional leaves until harvest to ensure normal growth and fruit quality. In commercial plantations of Cavendish bananas and Plantains , the disease is controlled through a combination of cultural practices, such as deleafing , and the application of fungicides , which are only effective on the pre-necrotic stages of the disease. Resistant cultivars have also been produced by breeding centres such as FHIA , and introduced to farmers, but no synthetic hybrid has yet been adopted by the export trade. Plant nutrition, water management and plant density are also part of an integrated approach to managing the disease. Chemical control The methods used to control BLSD have been informed by the experience controling Sigatoka leaf spot disease in Latin America and the Caribbean, starting with the ground spraying of Bordeaux mixture (suspension of copper sulphate, hydrated lime and water) in the 1930s.

The volumes applied decreased with the development of better spraying equipment but it became apparent that the rate at which leafs are emitted would impose a large number of applications to ensure that each new leaf is protected. In the 1950s, mineral oils were found to be excellent vehicles, either alone or mixed with water, for the contact fungicides that were starting to be used. Aerial spraying was also made possible by the change to oil. Mineral oilsnot only enhance the penetration of fungicides in the leaves, they also reduce leaching from rain. However, the accumulation of oil on the leaves interferes with gas exchange, and therefore photosynthesis. Moreover, under hot and dry conditions, the use of oil can be toxic to the plant, which shows up as water-soaked streaks on the leaves [10] . The first systemic fungicide, a Benzimidazole , was used in the early 1970s. Systemic fungicides provide better control than contact fungicides. On the other hand, disease management strategies that rely heavily upon them often lead to the selection of resistant fungal strains. The development of fungicide resistance has led to an increase in the number of fungicide applications.

In Costa Rica, for example, some 30 applications a year were the norm in the 1990s, compared to more than 50 in 2007 [9] . Growers caught in a strategy of systematic control to keep the disease in check manage fungicide resistance by alternating between contact and systemic fungicides. In regions where disease pressure is low and fungicide resistance has not been observed, it is possible to time the application of systemic fungicides when they are needed by using a biological forecasting system which is based on a standardized set of criteria that take into account the development of the fungus and the growth of the plant, both of which are climate driven. However, since systemic fungicides do not remove the disease from spotted leaves, the diseased parts of the leaves should be mechanically removed. Deleafing should be done regularly, taking into account that beyond a certain level it could affect bunch size. References Black sigatoka Figure 2. A banana plant. Symptoms and signs The first symptoms of black Sigatoka disease are tiny, chlorotic spots that appear on the bottom (abaxial) surface of the 3rd or 4th open leaf.

The spots grow into thin brown streaks that are limited by leaf veins (Figure 3). The color of the streaks becomes darker, sometimes with a purple tinge, and visible on the top (adaxial) surface. The lesions then enlarge, becoming fusiform or elliptical, and darken to give the characteristic black streaking of the leaves (Figure 4). Adjacent tissue often has a water-soaked appearance, especially under conditions of high humidity. Figure 3 Figure 4 When the disease severity is high, large areas of the leaf may become blackened and water-soaked. On the necrotic tissue, numerous, tiny, black, globose fruiting bodies (pseudothecia) containing sac-like structures (asci) filled with ascospores will emerge from the underside of the leaf (Figure 5). Figure 5 Black Sigatoka, first reported in Fiji in 1964, gets its name from appearing as a different form of yellow Sigatoka. It has black color in the young streaks and spots and lacks the distinct yellow halo that is present in young streaks of yellow Sigatoka.

Although the lesions of yellow Sigatoka (Mycosphaerella musicola) may look similar, one can distinguish between the yellow and black Sigatokas by examining conidiophore structure (see table below). Mycosphaerella fijiensis produces conidiophores in small groups and not in the larger clusters (sporodochia) produced by M. musicola. Also M. fijiensis has basal scars on the conidium and conidiophore at their points of attachment. Mycosphaerella fijiensis produces most of its asexual spores (conidia) and structures producing male sexual spores (spermagonia) on the underside of the leaf, whereas M. musicola produces conidia predominantly on the upperside of the leaf. Symptoms of yellow Sigatoka (Figures 6 and 7) typically develop more slowly than symptoms of black Sigatoka (Figure 8) (See below: Yellow and Black Sigatoka Compared). In addition, diagnosis can also be accomplished through the use of polymerase chain reaction (PCR).

Figure 6 Figure 7 Figure 8 If left unchecked, black Sigatoka will progress through the plant's leaf surface area, greatly reducing photosynthetic capability and thus yield (Figure 9). Figure 9 Black and Yellow Sigatoka Compared Pathogen more common in cooler environments inoculum consists of both conidia (water-dispersed) and ascospores (wind-dispersed) conidia first appear in the mature spot stage produce more than 30,000 condia per spot conidia not dislodged by wind mature ascospores produced 4 weeks after the appearance of streaks more common in warmer environments windborne ascospores are the major inoculum conidia first appear in early streak stage produce about 1200 condia per spot conidia both water- and wind-dispersed mature ascospores produced 2 weeks after the appearance of streaks Pathogen Biology Sexual reproduction Mycosphaerella fijiensis is the name given to the sexual form (teleomorph) of the pathogen. The fungus was first described in 1969 by Morelet on specimens from Fiji.

To produce the sexual form, the fungus first develops many spermagonia on the lower surface of the leaf as the lesions collapse. A spermagonium (Figure 10) is dark, somewhat erumpent, and pearlike in shape. In moist conditions these structures may ooze large quantities of the male reproductive cells (spermatia). Spermatia are tiny and cylindrical and will fertilize neighboring female receptive hyphae called trichogynes. Figure 10 Once fertilization is complete, pseudothecia are formed within the mature lesions, with their ostioles poking through the tissues (Figure 11). The oblong to club-shaped sac-like structures (asci) have two cell walls (bitunicate) and contain eight sexual spores (ascospores) that are lined up two-by-two. Pseudoparaphyses or sterile elements are absent from the pseudothecium. The ascospores are colorless and have one septum. One cell of the spore may be slightly broader than the other cell, and the spore may be slightly constricted at the septum. A squash mount of pseudothecia is shown in Figure 12.

Figure 11 Figure 12 Asexual reproduction The asexual form (anamorph) is called Pseudocercospora fijiensis. Conidia are borne on the conidiophore singly and terminally. The spores are pale to a light olive-brown, and are smooth, long, and have three or more septa (Figure 13). Figure 13 Figure 14 Conidia germinate during periods of high relative humidity (92-100% relative humidity) and infect the leaf through a stoma, usually on the underside of a leaf. Under humid conditions, hyphae can emerge from the stomata, grow along the leaf surface and penetrate through other stomata, thus enlarging the lesions. Conidiophores emerge through the stomata, sometimes on erumpent, compact masses of mycelium (stromata). Stromata may also develop on young spermagonia. Disease Cycle and Epidemiology Disease Cycle Epidemiology With black Sigatoka, ascospores, and to a certain extent conidia, are the propagules by which the fungus is dispersed. Conidia form readily in high humidity, especially if a film of free water is present on leaves.

These asexual spores disperse during rain-wash and splashing, causing local spread of the disease. Pseudothecia mature when dead leaf tissues are saturated with water for approximately 48 hours. Ascospores are the primary means of long distance dispersal and are the main means of spreading during extended periods of wet weather. Mycosphaerella fijiensis forms relatively few conidia, so ascospores are thought to be more important in the disease cycle. Sigatoka leaf spot on bananas decreases somewhat during the dry season but otherwise produces more or less continuously repeated cycles of infection (Figure 15). Figure 15 Disease Management Fungicides Large plantations are heavily reliant on chemical controls. Control programs are largely based on the protectant fungicides mancozeb, usually applied in water or in combination with oil, and chlorothalonil. Mancozeb is often combined or rotated with morpholine, demethylation inhibitors (DMI), or strobilurin (QoI) fungicides. Cholorothalonil is rotated but not combined with other fungicides. Resistance to benzimidazole, DMI, and strobilurin fungicides is widespread in many production areas.

The fungicides are often applied by airplanes (Figure 16). Figure 16 Biological Control Research into developing biological control methods for black Sigatoka has been limited since highly effective and affordable chemical controls are widely available for commercial growers. While biological control methods are desirable primarily for environmental reasons, their successful implementation is likely to be difficult since black Sigatoka is a polycyclic disease and susceptible banana tissue is present year-round. Various epiphytic bacteria (including Pseudomonas, Bacillus, and Serratia spp.) have been tested for controlling M. fijiensis, but biological control research is still in its preliminary stages. Resistant cultivars Use of resistant cultivars is really the only practical means of black Sigatoka control for the small-scale and subsistence farmer since fungicides are generally unaffordable. Unfortunately, while some resistant cultivars of plantains and bananas are available, they are often unacceptable to local tastes. Developing acceptable resistant cultivars is an important priority at international research centers (Figure 17). Figure 17 However, breeding for disease resistance is particularly difficult with banana plants.

Commercial bananas are autotriploids (AAA), i.e., they have three copies of the chromosome set instead of the two copies that the wild diploid species possess. While this extra chromosome set imparts favorable commercial characteristics such as seedlessness (unlike diploid wild species, Figure 18), as well as larger plant and fruit size, this high level of sterility is a major obstacle to banana breeders. Furthermore, the generation time (from seed to seed) for bananas is a long three years. Figure 18 Cultural management Cultural management techniques such as wider plant spacing, better drainage of both water and air, better weed management, and removal of severely diseased leaves or portions of them from plants can also be used to obtain some measure of control. Simply removing infected leaves (deleafing) and placing them on the ground can significantly reduce the efficacy of ascospore discharge (Figure 19). The application of urea and other products onto infested plant debris on the ground can accelerate decomposition and thus reduce further the available spore inoculum. Figure 19 Quarantine and Sanitation Proper quarantine and sanitation measures may provide some protection against two common means of long distance inoculum dispersal—leaves and rhizomes.

Contaminated banana leaves are often used to protect the fruit when transporting bananas by truck. Quarantine measures are practiced in some areas and countries where M. fijiensis has not yet been established or is confined to certain areas (Figures 20 and 21). Figure 20 Significance Losses and Economic Impact The black Sigatoka disease is particularly devastating. Under favorable conditions, leaf necrosis can reduce yields by 35-50%, and many important and commonly grown cultivars are susceptible. In 1995, the average cost for controlling this disease was US$1500/ha/yr. Annually, a typical plantation requires 38-50 fungicide sprays, and these sprays may account for around 30% of the production costs. In Central America, black Sigatoka may account for 27% of the total production cost, whereas other diseases and pests may account for only 3-5% of the total production cost. Generally, a minimum of five leaves on the plant at harvest is required for fruit quality to remain stable during transportation. Fruit from severely diseased plants are prone to premature and uneven ripening.

This is a grave concern for export producers, considering the exacting demands of consumers in developed countries. While large-scale operations can afford to spray, most small growers cannot afford chemical controls and so suffer losses. This poses a serious food security concern to subsistence farmers, particularly for those who rely heavily on plantains in their diets. In certain parts of Africa, plantains are the primary staple food (Figure 22). Figure 22 Selected References International Mycosphaerella Genomics Consortium (IMGC) Marín, D.H., R.A. Romero, M. Guzman, and T.B. Sutton. 2003. Black Sigatoka: an increasing threat to banana cultivation. Plant Dis. 87:208-222 . Ploetz, R.C., G.A. Zentmyer, W.T. Nishijima, K.G. Rohrbach, and H.D. Ohr. 1994. Compendium of Tropical Fruit Diseases. American Phytopathological Society Press. St. Paul, MN. Ploetz, R.C. 1999. Black Sigatoka of Banana: The most important disease of a most important fruit.

APSnet feature article: Promusa Website: Stover, R.H. 1980. Sigatoka leaf spot diseases of bananas and plantains. Plant Dis. 64:750-756. Stover, R.H. 1986. Disease management strategies and the survival of the banana industry. Ann. Rev. Phytopathol. 24:83-91. Thurston, H.D. 1998. Tropical Plant Diseases. American Phytopathological Society Press. St. Paul, MN. black Sigatoka (Mycosphaerella fijiensis) black Sigatoka (Mycosphaerella fijiensis) Leaves - necrotic areas Symptoms Symptoms are first visible as faint, minute, reddish-brown specks on the lower surface of the leaf. Specks elongate, becoming slightly wider, to form a characteristic narrow, reddish-brown streak with dimensions of 20 x 2 mm with the long axis parallel to leaf veins. Streaks frequently overlap to form compound streaks. The colour of streaks, which are now clearly visible on the upper leaf surface, changes to dark brown, almost black.

The entire leaf can blacken at this stage if streaks are numerous. If less densely congregated, streaks broaden and become fusiform or elliptical spots. Water-soaked borders appear around spots and surrounding leaf tissue yellows slightly. The centres of spots become slightly depressed and dry out, becoming light grey or buff. Each spot has a well-defined, narrow dark brown or black border and surrounding tissue is often yellow. Whole sections of leaves can become necrotic as spots coalesce. After the leaf has withered, spots remain visible because of their light-coloured centres. Different stages of disease development have been identified (Meredith and Lawrence 1969; Fouré, 1987). Often, all stages of disease development can be seen on one leaf. If inoculum pressure is high, leaves are rapidly destroyed. Often, fewer than six living leaves may be seen on a susceptible plant that is growing vegetatively. On resistant cultivars, symptoms are only usually seen on the older, lower leaves. The disease is more severe on plants with bunches because new leaves are no longer being produced to replace those lost due to disease.

If disease pressure is great, it is not uncommon for a susceptible cultivar to have no viable leaves at harvest. Prevention and control Cultural Control Removal and destruction of diseased leaves will reduce inoculum levels. If diseased leaves cannot be removed from the plot and burnt, they should be cut from plants and stacked on top of one another. This will prevent ascospores discharging effectively from the lower leaves in the pile. Overhead irrigation encourages disease and under-canopy micro-irrigation is preferable. Plants are also more prone to black leaf streak in sheltered areas where humidity levels are high. Good drainage systems that take surface water rapidly out of plantations can reduce humidity levels. Host-Plant Resistance Genetic resistance to black leaf streak is clearly the best long-term goal for disease control, especially for smallholders who cannot afford to purchase chemicals. Cultivars with high levels of resistance include 'Yangambi Km 5' (AAA), 'Mysore' (AAB), 'Pelipita' (ABB), 'Saba' (ABB) and 'Pisang Awak' (ABB). However, these do not suit all local tastes and some are susceptible to Fusarium wilt (Fusarium oxysporum f.sp.

cubense). Conventional banana breeding programmes utilize resistance to black leaf streak found in wild species of Musa, notably M. acuminata subsp. burmanicca, subsp. malaccensis and subsp. siamea, and in diploid cultivars such as 'Paka' (AA) and 'Pisang Lilin' (AA). Although a black leaf streak-resistant Cavendish-type dessert banana useful for the export trades has still to be developed, progress has been made towards breeding banana hybrids for local consumption. Plantain hybrids with good resistance have been bred by the International Institute for Tropical Agriculture (IITA), Nigeria, and by the Fundación Hondureña de Investigación Agricola (FHIA), Honduras. FHIA has also bred resistant dessert bananas hybrids which have fruit of a subacid or apple flavour and resistant robust cooking banana hybrids.

Other breeding programmes include the Centre de coopération internationale en recherche agronomique pour le développement (CIRAD) in Guadeloupe and the Centre de recherches sur bananiers et plantains (CARBAP) in Cameroon Biotechnological techniques, such as exploiting somaclonal variation, gamma irradiation and genetic engineering, are also being utilised in attempts to produce banana cultivars resistant to black leaf streak (Jones et al., 2000). Chemical Control Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources: - EU pesticides database ( ) - Your national pesticide guide Biological Control No biological control methodshave been adopted in commercial plantations. Some bacteria have shown promise, but the challenge of controlling this polycyclic fungus by biological methods is immense (Marin et al., 2003). Impact Black leaf streak disease of banana has spread to all major banana-growing regions of the world since it was first recognised in Fiji in 1963.

In the Pacific, it has been recorded in American Samoa, Australia (Torres Strait and Cape York Peninsula), the Cook Islands, Fiji, French Polynesia, Hawaii (USA), Micronesia, New Caledonia, Niue, Norfolk Island, Papua New Guinea, the Solomon Islands, Tonga, Vanuatu, Wallis and Fortuna Islands and Samoa. The disease has been found in many countries in Latin America namely Belize, Bolivia, Brazil (Amazonia), Colombia, Costa Rica, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Panama and Venezuela. In the Caribbean region, black leaf streak has been identified in Florida (USA), Cuba, Jamaica, the Dominican Republic and now poses a threat to the export industry based in the Windward Islands. West African countries with the disease are Benin, Cameroon, the Central African Republic, Congo, Côte d'Ivoire, the Democratic Republic of Congo, Gabon, Ghana, Nigeria, S¦o Tomé and Togo. In the East African region, black leaf streak has been found in Burundi, Comoros, Kenya, Madagascar, Malawi, Mayotte, Rwanda, Tanzania (including Zanzibar), Uganda and possibly Zambia.

Bhutan, China (Hainan, Guangdong and Yunnan), Indonesia (Halmahera, Java, Kalimantan and Sumatra), Malaysia (Johore, Langkawi Island and Sarawak), the Philippines, Singapore, Taiwan, Thailand and Vietnam have been found with the disease in Asia. However, the situation is more confused in this region because M. fijiensis is not common at all locations. Competition from other leaf spots and the diversity of banana germplasm with varying degrees of disease resistance may account for its erratic distribution (Carlier et al., 2000; Jones, 2003). Black leaf streak is a major constraint to banana production in most countries where it occurs (Stover, 1983, 1986; Fouré, 1985; Fullerton, 1987; Stover and Simmonds, 1987). After the first occurrence of black leaf streak in an area, the disease usually builds up and often reaches an epidemic level in a few years (Fullerton and Stover, 1990; Belalcazar, 1991).

Chemical control costs and crop losses are well documented for industrially produced bananas (Stover, 1986, 1990). Losses to smallholders' crops that are consumed locally are harder to estimate. Black leaf streak does not kill plants immediately, but crop losses increase gradually with the age of plantings. The decrease in functional leaf area caused by the disease results in a reduction in the quality and quantity of fruit (Stover, 1983; Stover and Simmonds, 1987; Pasberg-Gauhl, 1989; Mobambo et al., 1993, 1996b). Fruit from infected plants ripens prematurely and does not properly fill. Bananas for export are sometimes harvested at a lower grade (younger age) in order to reduce the risks of premature ripening in transit to overseas markets (Stover and Simmonds, 1987). Until the 1970s, the common leaf diseases of plantain were not considered economically important. This changed when black leaf streak spread to areas where the crop was extensively grown. All over the tropics, plantain is cultivated and fruit consumed by smallholders.

In many areas, black leaf streak has caused a considerable decrease in the availability of fruit for local consumption and this has resulted in a substantial increase in their market price. Smallholders growing plantain in the Americas either go out of business, because they cannot cover the high costs of chemical control, or form cooperatives so that their limited resources can be pooled to fight the disease. Black leaf streak is endangering the food security of resource-poor people. Africa alone contributes about 50% of the world plantain production and the demand for plantain is steadily increasing (Wilson, 1987). All known plantain cultivars (Fouré, 1985; Mobambo et al., 1996a) are susceptible to black leaf streak and are severely defoliated by the disease. Plants in the ratoon crop are weaker than in the first cycle and thus more affected by wind damage. On poor sandy soils in West Africa, Mobambo et al. (1996b) estimated that yield losses due to black leaf streak are 33% and 76% during the first and second cropping cycle respectively.

However, in intensively cropped backyard or home garden systems, cultivation is not so seriously affected (Mobambo et al., 1994). Under marginal conditions, plantain production is often abandoned due to low yields. Plantain is not the only smallholder banana to be affected in Africa. The disease also causes serious damage to East African highland cultivars in the Lujugira-Mutika subgroup (AAA). In Uganda, Tushemereirwe (1996) reported yield losses of 37% due to the effects of a leaf spot complex consisting mainly of black leaf streak and Cladosporium leaf speckle. Black leaf streak has had a devastating effect on the production of export bananas in the South Pacific. Firman (1972) noted that only 49% of unsprayed Cavendish cultivars produced fruit that reached the export quality standard. Fiji ceased exporting bananas in 1974 and Samoa in 1984. Exports also dropped in Tonga and the Cook Islands, because producers had problems maintaining fruit quality standards for their markets in New Zealand. Black leaf streak control has become the single largest production cost (Fullerton, 1987).

In 1974, the production of dessert bananas and plantains in Central America was seriously affected by hurricane Fifi, which was also thought to be responsible for the wind borne spread of black leaf streak to new areas. In many countries, production subsequently dropped substantially. Before 1974, Honduras exported 500,000 boxes of plantain each year, but afterwards exports dropped to below 1,000 boxes (Stover, 1983). In 1978, the export of plantain from Honduras to the USA was curtailed because of the shortage of fruit with the required quality (Bustamente, 1983). Plantain exports only resumed in 1985, when black leaf streak was controlled by the aerial application of fungicides (Stover, 1987). After the identification of black leaf streak in Costa Rica in 1979, the government initiated a quarantine programme (Woods, 1980). This programme consisted of the destruction of host plants in the affected area and the establishment of roadside quarantine stations strategically located to stop movements of banana and plantain leaves which were used for padding and shading fruit.

About 3,000 hectares of plantain were destroyed in 1979 and early 1980. The Costa Rican government paid about US$ 3 million for the eradication program, but the spread of the disease could not be stopped (Woods, 1980). By 1982, the Ministry of Agriculture in Costa Rica estimated that black leaf streak alone reduced plantain production by 40% (Romero, 1986). In general, yields of plantains in well maintained fields on rich fertile soils in Central America may have fallen by 20-50% (Stover, 1983a; Pasberg-Gauhl, 1989). Black leaf streak was first detected in Panama in 1980. Bureau (1990) estimated that plantain production in Panama decreased by 69% between 1979 (100,910 t) and 1984 (31,134 t). During this period, the price of plantains rose by up to 50% in local markets.

Jaramillo (1987) reported that between 1982 and 1985, the area planted with plantain decreased by 22% from 7432 ha to 5800 ha. About 34% of growers were believed to have abandoned their holdings leading to a decrease in production of 47%. Colombia is one of the largest plantain producers in Latin America with 400,000 ha under cultivation and an estimated yearly production of 2.5 million t. About 96% of plantains are consumed locally, the remainder being exported (Belalcazar, 1991). Smallholders grow about 88% of the plantain in association with coffee. Only 12% of the crop is grown in monoculture in larger plantations. After the introduction of black leaf streak, this staple food became scarce and much higher prices were demanded in the market (Belalcazar, 1991). Due to the high cost of plantain, consumers changed to other, cheaper food crops. This in turn had a negative effect on plantain production.

Black leaf streak has thus had a significant impact on Colombian agriculture and the eating habits of a nation. Black leaf streak can be chemically controlled on plantations, but the cost is substantial. Up to 36 spray cycles per year may be required for plantations growing dessert bananas for export and up to 19 cycles for commercial plantings of plantain (Fouré, 1983, 1988a, b; Stover, 1980b, 1990; Belalcazar, 1991; Gauhl, 1994; Romero and Sutton, 1997b). Stover and Simmonds (1987) reported that 27% of production costs in dessert banana plantations was spent controlling black leaf streak. From 1972 until 1985, the estimated cost of black leaf streak control in Central America, Colombia and Mexico was more than US$ 350 million (Stover and Simmonds, 1987).

The cost of chemical control measures has been calculated to be US$ 400-1,400 per ha per year (Anon., 1993). During the 1980s, the cost of black leaf streak control in export banana crops in Costa Rica was estimated at approximately US$ 17.5 million per year (Stover and Simmonds, 1987). Between 1985 and 1994, the area under banana cultivation increased from approximately 21,000 ha to 52,737 ha (Serrano and Marín, 1998). As a consequence, the cost of black leaf streak control in 1995 was estimated to have increased to US$ 49 million per year (Romero and Sutton, 1997b). Recent information from Venezuela indicates that the cost of black leaf streak control in plantain farms south of Lake Maracaibo amounts to almost 50% of production costs.

However, even with control measures being taken, yields were still 25% below those before the appearance of the disease in that country (Zabala and Bermudez, 1999). Related treatment support

Question: Black Sigatoka is a leaf spot disease of which fruit plant?
Answer: Banana