bluuebunny/crossref_metadata_2025 huggingface dataset:
Vegetative Compatibility and Seasonal Variation Among Isolates of Sclerotinia homoeocarpa
Authors: Powell J. F. , Vargas J. M.
Published: May 2007

Dollar spot of amenity turf, caused by Sclerotinia homoeocarpa, occurs in two seasonal epidemics in the northern United States, one from May to late July and a second from mid-August through October. It is not known whether these seasonal epidemics are the result of multiple species or due to seasonal variation within a single species. Isolates of S. homoeocarpa were collected from dollar spot lesions obtained from golf courses in Michigan, Illinois, and Wisconsin. Vegetative compatibility reactions between isolates identified six vegetative compatibility groups (VCGs) among more than 1,300 isolates collected from the eight locations. Most VCGs were present throughout the season, but one was generally recovered only in the late epidemic. Sequences of the nuclear ribosomal internal transcribed spacer 1 (ITS1) were identical among VCGs, indicating that the VCGs represent a single species. The results of this study suggest that the seasonal dollar spot epidemics observed in the northern United States are caused by a single species.
Septoria tritici Blotch Development as Affected by Temperature, Duration of Leaf Wetness, Inoculum Concentration, and Host
Authors: Chungu C. , Gilbert J. , Townley-Smith F.
Published: May 2007

The effects of incubation temperature, leaf-wetness duration, inoculum concentration, and interaction between leaf-wetness duration and inoculum concentration on the development of Septoria tritici blotch were evaluated at the seedling stage in two bread wheats (Katepwa and 6 Lacos-78) and two durum wheats (AC Melita and Kyle). The study was conducted to assess if bread and durum cultivars widely grown in Manitoba and a resistant cultivar from South America react differently to the disease at temperatures characteristic of Manitoba summers, and to obtain information on conditions that would be used in differentiating resistant and susceptible cultivars under controlled conditions. The experiments were carried out under three temperature regimes. Factors that evaluated included inoculum concentration and duration of leaf wetness. Increasing incubation temperature, duration of leaf wetness, and inoculum concentration resulted in an increase in disease severity. There were significant (P < 0.05) differences for duration of leaf wetness and inoculum concentration within each cultivar. Pycnidia were observed 4 days earlier when incubation temperature increased from 18°C day/15°C night to 22°C day/15°C night or when inoculum concentration increased from 1 × 106 spores/ml to 1 × 107 spores/ml. There were more pycnidia when duration of leaf wetness was 72 h as opposed to 48 h and 60 h. The cultivar that was presumed to be resistant maintained its resistance under environmental conditions that are characteristic of Manitoba summers. We found that the optimal conditions for screening spring wheats for Septoria tritici blotch reaction were incubation temperatures of 18°C day/15°C night, and 22°C day/15°C night. Leaf wetness duration of 48 or 72 h and inoculum concentration of 1 × 107 spores/ml consistently produced a susceptible reaction on Katepwa, AC Melita, and Kyle the three cultivars that were susceptible to Septoria tritici blotch.
New Hosts of the Parasitic Flowering Plant, Alectra vogelii, in Malawi
Authors: Subrahmanyam P.
Published: May 2007

Alectra vogelii Benth. (Family: Scrophulariaceae) is a vascular hemiparasite of various leguminous crops in Africa, including peanut (Arachis hypogaea), bambara groundnut (Vigna subterranea), cowpea (Vigna unguiculata), common bean (Phaseolus vulgaris), soybean (Glycine max), and mung bean (Vigna radiata) (1). It is a common parasite of peanut in Angola, Burkina Faso, Malawi, Mozambique, Nigeria, Swaziland, Zambia, and Zimbabwe (2). During April and May 2000, A. vogelii was observed parasitizing several wild Arachis species in a field at the Chitedze Agricultural Research Station near Lilongwe, Malawi. These species were part of a germ plasm enhancement program that included A. appressipila (ICRISAT Groundnut Accession number [ICG] 8127), A. batizocoi (ICG 8124), A. benensis (ICG 13215), A. cardenasii (ICG 13164 and 13166), A. correntina (ICG 8918), A. duranensis (ICG 13200), A. helodes (ICG 8955 and 14917), A. hoehnei (ICG 13228), A. magna (ICG 8960), A. pintoi (ICG 13222 and 14914), A. stenosperma (ICG 13172 and 13223), and A. valida (ICG 13230). In addition, A. vogelii was observed on four unidentified Arachis species (ICG 13231, 14875, 14888, and 14907). Parasitized plants were less vigorous and connections between A. vogelii and host plants could be observed by carefully removing the soil in the root zone. Mature A. vogelii plants were 0.3 to 0.5 m and had multiple stems branching at the base. Subsoil plant parts were a deep orange color. Flowers were prominent lemon yellow with horseshoe-shaped stigmata and leaves were light green. This is the first report of A. vogelii parasitizing wild Arachis species.

References: (1) C. Parker. Crop Prot. 10:6–22, 1991. (2) P. Subrahmanyam. 1997. Parasitic flowering plants. Pages 70–71 in: Compendium of Peanut Diseases, 2nd Ed. N. Kokalis-Burelle, D. M. Porter, R. Rodriguez-Kabana, D. H. Smith, and P. Subrahmanyam, eds. American Phytopathological Society, St. Paul, MN.
Outbreak of Clover yellow vein virus in a Bean Field in Colusa County, California
Authors: Crnov R. , Gilbertson R. L.
Published: May 2007

In 1999, a severe outbreak (i.e., 100% infection) of a virus disease was observed in a single field of common bean in Colusa County, CA. The symptoms included a yellow mosaic, leaf epinasty and, in some plants, a systemic necrosis. This field was adjacent to a clover field that had been harvested early in the development of the bean plants. A preliminary serological test (enzyme-linked immunosorbent assay, ELISA) suggested that the virus infecting these bean plants was Peanut mottle virus (PeMoV). This would represent the first report of this virus in California. A range of common bean cultivars (Black Turtle Soup, Topcrop, California Early Light Red Kidney, and Sutter Pink) were inoculated with sap prepared from symptomatic leaves collected from this field. Symptoms developing on these plants ranged from systemic necrosis (cvs. Sutter Pink and Black Turtle Soup) to strong yellow green mosaic and leaf distortion (cvs. Topcrop and California Early Light Red Kidney). Furthermore, inoculated primary leaves of cv. Topcrop failed to develop local lesions, which is characteristic of PeMoV. ELISAs on all symptomatic plants with antisera against PeMoV, BYMV, BCMV, and BCMNV as well as reverse transcription polymerase chain reaction (RT-PCR) analysis with primer pairs specific for PeMoV, BYMV, BCMV, and BCMNV were negative. To further investigate the nature of this virus, a minipurification method was used to purify virions from symptomatic leaves of all four cultivars. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of purified virions from these cultivars revealed a 32-kDa band consistent with infection by a potyvirus. Transmission electron microscopy analysis of these preparations revealed the presence of potyvirus-like flexous rods (approximately 750 nm long and 10 nm wide). We next designed a primer pair specific for the coat protein gene of Clover yellow vein virus (ClYVV) and RT-PCR with these primers resulted in the amplification of a 630-bp DNA fragment from four isolates of the unknown potyvirus. No fragments were amplified from an uninfected control. The PCR-amplified fragments were direct-sequenced, and sequence comparisons revealed that the sequences of all four isolates were 95% identical to that of ClYVV (Genbank accession number D89541). Subsequently, a ClYVV antiserum was obtained from Simon Scott (Department of Plant Pathology, Clemson University), and ELISAs performed on leaves infected with all four isolates were positive. Finally, to assess whether the virus was seed-transmitted, seed harvested from this field was planted in a greenhouse (two lots of 400 seed each). None of the plants from these seeds developed virus symptoms, suggesting that the virus was not seed-transmitted. Together, these results indicate that the virus disease outbreak in this bean field was caused by ClYVV rather than PeMoV. The inoculum source for the virus was probably the adjacent clover field. This is the first report of ClYVV infecting common bean in California.
Host Range and Alternate Host of a Puccinia coronata Population from Smooth Brome Grass
Authors: Delgado N. J. , Grau C. R. , Casler M. D.
Published: May 2007

A rust fungus was observed on smooth brome grass (Bromus inermis Leyss.) leaves growing in the fields of the University of Wisconsin (UW) Agricultural Research Station at Arlington, WI. The population (WPc-95A) was classified as Puccinia coronata Corda. Reports of P. coronata on B. inermis are rare, so a study of the pathogen host range, alternate host, and morphology of urediniospores and teliospores was undertaken. Fourteen grass species representing 10 genera were inoculated with P. coronata WPc-95A, which was maintained with repeated inoculations on B. inermis cv. PL-BDR1. Seventy-two 30-day-old seedlings of B. inermis were inoculated with urediniospores of the fungus. Infection type, pustule density, and disease incidence were recorded 15 days after inoculation. The same grass cultivars were also inoculated with aecio-spores collected from Rhamnus cathartica L. located on the UW campus. To test for host specificity, urediniospores produced on aeciospore-susceptible grass species were used to reinoculate plants of B. inermis and the host species from which the urediniospores were derived. B. inermis, B. riparius Rehm., Festuca pratensis Huds., and Lolium perenne L. were susceptible to P. coronata WPc-95A. The two Bromus spp. had the highest disease incidence. R. cathartica was found to be an alternate host of P. coronata WPc-95A, as it is for P. coronata isolates found on F. pratensis. However, cross-inoculations with urediniospores from R. cathartica-derived aeciospore infections indicated that only urediniospores of B. inermis origin were capable of infecting B. inermis. Thus, P. coronata WPc-95A appears to belong to a forma speciales previously undescribed in North America.
Biological Control of Fungal Strawberry Diseases by Serratia plymuthica HRO-C48
Authors: Kurze Stefan , Bahl Hubert , Dahl Robert , Berg Gabriele
Published: May 2007

To develop a biological control product for commercial strawberry production, the chitinolytic rhizobacterium Serratia plymuthica strain HRO-C48 was evaluated for plant growth promotion of strawberries and biological control of the fungal pathogens Verticillium dahliae and Phytophthora cactorum. In phytochamber experiments, treatment with S. plymuthica HRO-C48 resulted in a statistically significant enhancement of plant growth dependent on the concentration of the bacterium that was applied. In greenhouse trials, bacterial treatment reduced the percentage of Verticillium wilt (18.5%) and Phytophthora root rot (33.4%). In three consecutive vegetation periods, field trials were carried out in soil naturally infested by both soilborne pathogens on commercial strawberry farms located in various regions of Germany. Dipping plants in a suspension of S. plymuthica prior to planting reduced Verticillium wilt compared with the nontreated control by 0 to 37.7%, with an average of 24.2%, whereas the increase of yield ranged from 156 to 394%, with an average of 296%. Bacterial treatment reduced Phy-tophthora root rot by 1.3 to 17.9%, with an average of 9.6%, and increased strawberry yield by 60% compared with the nontreated control. Under field conditions, strain HRO-C48 survived at approximately log10 3 to 7 CFU/g of root in the strawberry rhizosphere at 14 months after root application. Although results of the field trials were influenced by pathogen inoculum density, cropping history of the field site, and weather conditions, S. plymuthica HRO-C48 successfully controlled wilt and root rot of strawberry.
Development of Brown Patch and Pythium Blight in Tall Fescue as Affected by Irrigation Frequency, Clipping Removal, and Fungicide Application
Authors: Settle D. M. , Fry J. D. , Tisserat N. A.
Published: May 2007

We studied the effects of irrigation frequency, clipping removal, and fungicide application on the development of Rhizoctonia brown patch (Rhizoctonia solani) and Pythium blight (Pythium aphanidermatum) in tall fescue. Brown patch severity was not significantly different between plots irrigated daily and those irrigated on alternate days. Similarly, no differences in brown patch were observed in plots where grass clippings were returned to the sward with a mulching mower compared with plots where clippings were removed. Preventive applications of azox-ystrobin at 35-day intervals or postinfection applications of chlorothalonil reduced brown patch severity, but only the azoxystrobin treatment provided aesthetically acceptable (<10%) levels of brown patch control. However, azoxystrobin applications also increased Pythium blight compared with untreated or chlorothalonil-treated tall fescue, especially in plots that received daily irrigation.
Biological and Molecular Characterization of Moroccan watermelon mosaic virus and a Potyvirus Isolate from Eastern Sudan
Authors: Lecoq Hervé , Dafalla Gasim , Desbiez Cécile , Wipf-Scheibel Catherine , Delécolle Brigitte , Lanina Tanya , Ullah Zakir , Grumet Rebecca
Published: May 2007

A potyvirus (Su-94-54) was isolated from a naturally infected snake cucumber (Cucumis melo var. flexuosus) plant with severe mosaic and leaf deformation symptoms collected in Eastern Sudan. This isolate has a host range limited to cucurbits and is serologically distantly related to Moroccan watermelon mosaic virus (MWMV) and to Papaya ringspot virus (PRSV). Coat protein sequence analysis of Su-94-54 and MWMV and comparison with other potyviruses indicate that Su-94-54 is more closely related to MWMV than to any other potyvirus. Based on the amino acid sequence identity in the core part of the coat protein with MWMV (86%), this isolate could be regarded as a distinct species. However, because of biological, cytological, and serological affinities with MWMV, we propose that this isolate be considered as a strain of MWMV, possibly an evolutionary intermediate between MWMV and PRSV, until more is known on the structure of the PRSV subgroup within the genus Potyvirus.
Temperature Effects on the Disease Reactions of Sunflower to Infection by Orobanche cumana
Authors: Sukno S. , Fernández-Martínez J. M. , Melero-Vara J. M.
Published: May 2007

Three virulent populations (CU194, SE193, and SE194) of the parasitic plant Orobanche cu-mana were inoculated onto four lines (KA-41, J-8281, HA-89, and RHA-273) of sunflower (Helianthus annuus L.). Pots were transferred to growth chambers set at 15, 19, 23, and 27°C. Emergence of broomrape plants and infection incidence were determinants of disease reaction. All broomrape populations were pathogenic to the sunflower lines KA-41, HA-89, and RHA-273, although differences in virulence were found. At 15 to 23°C, the populations of broomrape infected these three sunflower lines, but a delay in emergence of broomrape was found at 15°C; whereas, at 27°C, the level of infection was restricted. Only population CU194 infected the resistant line J-8281, with infection occurring mainly at 23 and 27°C, but few broomrape plants emerged. Our results suggest that the effect of temperature on the host-parasite relationship is complex.
First Occurrence of a Rust Fungus on English Daisy (Bellis perennis) in North America
Authors: Koike S. T. , Scholler M. , Herbaria Arthur , Herbaria Kriebel
Published: May 2007

English daisy (Bellis perennis, family Asteraceae) is a flowering plant native to Europe. It is widely used as an ornamental in North America but is also a weed in lawns in the western and eastern United States. In December 2000, plants growing in urban landscapes in Monterey County, CA, were infected with rust. Orange aecia containing aeciospores that measured 14 to 18 × 12.5 to 15 μm developed profusely on leaves. Severely diseased leaves wilted and collapsed. Other spore states (pycnia, uredosori, and telia) were not observed. Based on the size and ornamentation of the aeciospores, reduced white peridium, apperance of the peridial cells, and arrangement of sori, we identified the pathogen as Puccinia lagenophorae Cooke (1,3), a rust fungus native to Australia and New Zealand that since 1960 has been introduced to other continents (2). On English daisy, the disease has been reported only in Australia and Europe (1). The pathogen also occurs on numerous other plants of the subfamily Asteroideae (family Asteraceae) (2). The occurrence of P. lagenophorae on English daisy follows the recent, first-time detection of the same pathogen on common groundsel (Senecio vulgaris) in California (3). To test cross infectivity, a spore suspension of a rust isolate from common groundsel was prepared and applied to various ornamental plants known to be hosts of P. lagenophorae. Inoculated plants were kept in a humidity chamber for 48 h, then maintained in a greenhouse. After 9 to 14 days, aecia developed on English daisy, cineraria (S. cruentus), and common groundsel but did not develop on dusty miller (S. cineraria) or pot marigold (Calendula officinalis). In addition, a single telium, surrounded by aecia, was observed on one of the infected English daisy plants. The telium contained two-celled teliospores that measured 31 to 36.5 × 16 to 19 (-22) μm and one-celled mesospores that measured 22 to 34 × 13.5 to 16 μm. At point of attachment, the widths of the stalks measured 7 to 8.5 (-9.5) μm. Some of the spores had surface ridges. The morphological features of the telio- and mesospores agree with those described for P. lagenophorae. To the authors' knowledge, this is the first record of a rust fungus on English daisy in North America. The inoculation experiments indicated that the rusts on English daisy and common groundsel are not biologically separated, casting doubt on the taxonomic concept of Weber et al. (4) that considered the rust on English daisy to be a distinct species, P. distincta McAlpine (although they did not examine type material of either P. lagenophorae or P. distincta).

References: (1) M. Scholler. Sydowia 49:174, 1997. (2) M. Scholler. J. Plant Dis. Prot. 105:239, 1998. (3) M. Scholler and S. T. Koike. Plant Dis. 85:335, 2001. (4) R. W. S. Weber et al. Mycol. Res. 102:1227, 1998.
Yellow Nutsedge (Cyperus esculentus L.) as a Host of Sclerotinia minor
Authors: Hollowell J. E. , Shew B. B.
Published: May 2007

Sclerotinia minor Jagger is a major pathogen of peanut (Arachis hypogaea L.) in North Carolina, Virginia, Oklahoma, and Texas. Economic crops that are hosts to S. minor are seldom grown in rotation with peanut, and the pathogenicity of S. minor to most weed species commonly found in peanut fields is unknown. In September 2000, signs and symptoms of Sclerotinia infection were observed on plants of yellow nutsedge growing in peanut fields in Bertie County, NC. Fluffy white mycelium, water soaked and bleached areas of the leaves were observed on basal portions of plants. Isolations were made from a symptomatic plant growing in a peanut field at the Peanut Belt Research Station at Lewiston-Woodville, NC. Small portions (1 to 2 cm) of symptomatic leaves were placed on potato dextrose agar (PDA) and pure cultures typical of S. minor were obtained. Small black irregular-shaped sclerotia (<2 mm) were produced abundantly and scattered over the culture surface (1). Pathogenicity was tested by placing agar plugs of mycelium of the fungus between the leaf blades of potted mature yellow nutsedge plants. Plants were misted with water, enclosed in plastic bags, and incubated on a lab counter top at ambient temperature (˜24°C). Mycelia developed after 3 to 4 days and chlorotic leaves appeared by day 7. Sclerotia were observed in 11 days on seedheads, which were distal from the site of inoculation. Uninoculated plants did not develop symptoms. The fungus was reisolated on PDA, and typical cultures of S. minor with small sclerotia were obtained. The nutgrass isolate was inoculated onto detached peanut leaves and typical symptoms developed. This is the first report of yellow nutsedge as a host of S. minor.

Reference: (1) L. M. Kohn. Mycotaxon 9:365–444, 1979.
Phytophthora Species Associated with Crown and Root Rot of Apple in Chile
Authors: Latorre B. A. , Rioja M. E. , Wilcox W. F.
Published: May 2007

Phytophthora cactorum, P. cryptogea, P. gonapodyides, and P. megasperma were isolated from necrotic root and crown tissues or the rhizospheres of apple trees exhibiting typical symptoms of Phytophthora root and crown rot in the Central Valley of Chile. Representative isolates of all four species were pathogenic on a variety of apple rootstocks and scions in trials conducted on excised shoots and 1-year-old MM.106 rootstock grown for 4 months in infested potting medium. P. cactorum was the most frequently isolated species and the most virulent in pot tests, although a significant Phytophthora sp.-apple genotype interaction was observed. This is the first report of any species other than P. cactorum causing root and crown rot of apple trees in Chile.
PCR Detection of Fusarium oxysporum f. sp. basilici on Basil
Authors: Chiocchetti Annalisa , Sciaudone Lucia , Durando Fiorenza , Garibaldi Angelo , Migheli Quirico
Published: May 2007

Sixty-nine amplified DNA fragments, generated from different isolates of Fusarium oxysporum f. sp. basilici, were tested for F. oxysporum f. sp. basilici-specificity in a dot blot assay. One 1,038-bp fragment hybridized to DNA from all F. oxysporum f. sp. basilici isolates but not to DNA obtained from F. oxysporum isolates nonpathogenic to basil or representatives of other formae speciales of F. oxysporum, or from isolates of F. redolens, F. tabacinum, Rhizoctonia solani, Sclerotinia sclerotiorum, S. minor, and Pythium ultimum obtained from diseased basil. This fragment was cloned and sequenced, and three pairs of F. oxysporum f. sp. basilici-specific primers were designed, giving rise to amplification products of 943, 382, and 330 bp. A nested PCR assay allowed detection of F. oxysporum f. sp. basilici in diseased seedlings and in artificially and naturally contaminated seeds. The theoretical detection limit of this system was 102 fungal propagules per 100 seeds on artificially contaminated samples, while on naturally contaminated commercial seed lots, 32 propagules per 100 seeds were detected.
First Report of Tomato yellow leaf curl virus on Tomato Crops in Greece
Authors: Avgelis A. D. , Roditakis N. , Dovas C. I. , Katis N. I. , Varveri C. , Vassilakos N. , Bem F.
Published: May 2007

In late summer 2000, tomato (Lycopersicon esculentum Mill.) grown in greenhouses in Ierapetra, Tympaki, and Chania (Crete) showed leaf curling, reduced leaf size, yellowing, shortened internodes, and a bushy appearance. More than 30 ha of tomato greenhouses were affected and the disease incidence ranged from 15 to 60% with estimated crop losses of over $500,000. Similar symptoms were observed in tomato samples from Marathon (Attiki) and Southern Peloponnese. All greenhouses with infected plants were infested with high populations of Bemisia tabaci (Gennadius), which were also observed outside the greenhouses on several weeds. Tomato symptoms were similar to those caused by Tomato yellow leaf curl virus (TYLCV). The assumed virus could not be transmitted mechanically but successful transmission was obtained by grafting onto healthy tomato plants. Over 100 samples of symptomatic tomato plants collected from Crete and southern Peloponnese gave positive reactions when tested by ELISA using monoclonal antibodies to TYLCV-European (Adgen Ltd). The serological results were confirmed by PCR using two pairs of primers, universal degenerate (1) and MA 13 and MA 17 (2), amplifying different parts of the virus genome. The restriction fragment length polymorphism (RFLP) analysis (AluI, HaeIII, and TaqI) of the 541 bp amplicon obtained with the degenerate primers showed patterns similar to TYLCV-Is (Israeli species). The second pair of primers gave the expected 348 bp product, which was sequenced. Sequence comparisons revealed 99% identity with TYLCV-Is (EMBL no. X15656, X76319). The resulting sequence was at least 97.7% identical to sequences of TYLCV isolates from the Dominician Republic (EMBL no. AF024715), Cuba (EMBL no. AJ223505), Portugal (EMBL no. AF105975), Iran (EMBL no. AJ13271), and Spain (EMBL no. AF071228). The disease appeared for the first time in 1992 in Tymbaki, but was limited to very few plants in one glasshouse. However, the cause was not determined. To our knowledge, this is the first report of TYLCV of the Begomovirus genus in Greece.

References: (1) D. Deng et al. Ann. Appl. Biol. 125:327, 1994. (2) J. Navas-Castillo et al. J. Virol. Methods 75:195, 1998.
Seed Transmission of the High Plains virus in Sweet Corn
Authors: Forster R. L. , Seifers D. L. , Strausbaugh C. A. , Jensen S. G. , Ball E. M. , Harvey T. L.
Published: May 2007

The High Plains virus (HPV), which infects corn and other cereals, was first found in 1993 in the United States. Research was initiated in 1995 to investigate the potential for seed transmission of HPV. Sweet corn seeds of various cultivars harvested in 1994 to 1996 from 13 fields and research plots in southwestern Idaho, Colorado, and Nebraska were seeded in potting mix in the greenhouse. Leaf samples collected at the three- to six-leaf stage from both symptomatic and asymptomatic plants were tested by enzyme-linked immunosorbent assay (ELISA). Of the 46,600 seeds planted, 38,473 seedlings emerged, and three tested positive by ELISA, exhibited mosaic symptoms, and had the presence of HPV confirmed by an additional test. One of the positive plants was used for successful acquisition and transmission of HPV by the wheat curl mite to Westford barley. The other two plants were used to successfully transfer HPV to other corn plants by vascular puncture inoculation of seed. These results indicate that HPV can be seed transmitted at a very low frequency in sweet corn.
Soybean Cyst Nematode Population Development and Associated Soybean Yields of Resistant and Susceptible Cultivars in Minnesota
Authors: Chen S. Y. , Porter P. M. , Orf J. H. , Reese C. D. , Stienstra W. C. , Young N. D. , Walgenbach D. D. , Schaus P. J. , Arlt T. J. , Breitenbach F. R.
Published: May 2007

The soybean cyst nematode (SCN), Heterodera glycines, is a major soybean yield-limiting factor, and the use of resistant cultivars is one of the most effective means to manage the nematode. During the past decade, a number of resistant cultivars in maturity groups I and II have been developed and made available to growers. A total of 47 resistant cultivars and nine susceptible cultivars were evaluated at 15 SCN-infested field sites and two noninfested sites during 1996 to 1998 in Minnesota. As expected, more nematodes developed on susceptible cultivars than on resistant cultivars. Egg density on susceptible cultivars increased by 1.9- to 10.6-fold during the growing season at 12 sites and did not change at the other three sites. Average egg density decreased over time for resistant cultivars at all sites, except where the initial egg density was low (≤455 eggs per 100 cm3 soil). Nematode reproduction factors (Rf = egg density at harvest/egg density at planting) for individual resistant and susceptible cultivars were highly consistent across the eight sites where initial SCN density was more than 1,000 eggs per 100 cm3 soil. Resistance, however, varied among the cultivars, with the average Rf of individual resistant cultivars across the sites ranging from 0.3 to 1.7. Resistant cultivars produced an average yield of 3,082 kg/ha compared with 2,497 kg/ha by susceptible cultivars at eight of 10 sites where egg density at planting was greater than 700 eggs per 100 cm3 soil. In contrast, no difference in yield was observed between resistant and susceptible cultivars at sites where egg density at planting was lower than 500 eggs per 100 cm3 soil. Yield differences between resistant and susceptible cultivars increased with increasing initial SCN egg density. In six fields infested with initial densities of more than 5,000 eggs per 100 cm3 soil, resistant cultivars produced 28.4% (676 kg/ha) more yield on average than susceptible cultivars. Soybean yield increased when cultivars with increasing resistance to the SCN (lower Rf or females formed on roots) were grown in fields infested with SCN. Average relative yield (yield of a cultivar/average yield of all resistant cultivars at a site) of individual resistant cultivars across all SCN-infested sites ranged from 0.76 to 1.10. Yield consistency of soybean cultivars was low among the different sites, indicating that many other factors affected yield. Our results suggest growing resistant cultivars is an effective method to manage SCN in Minnesota while minimizing yield loss due to SCN.
Influence of Cropping Systems on Stem Rot (Sclerotium rolfsii), Meloidogyne arenaria, and the Nematode Antagonist Pasteuria penetrans in Peanut
Authors: Timper P. , Minton N. A. , Johnson A. W. , Brenneman T. B. , Culbreath A. K. , Burton G. W. , Baker S. H. , Gascho G. J.
Published: May 2007

The effect of crop rotation (main plots) and pesticide treatment (subplots) on stem rot (Sclerotium rolfsii), Meloidogyne arenaria, and the nematode antagonist Pasteuria penetrans was determined in a field experiment. The field site was naturally infested with all three organisms. Peanut (P) was rotated with 2 years of either cotton (Ct), corn (C), or bahiagrass (B). The pesticide treatments for the peanut crop were aldicarb (31 g a.i. per 100-m row), flutolanil (1.7 kg a.i./ha), aldicarb + flutolanil, and a control without either pesticide. Populations of M. arenaria were lower in peanut in the Ct-Ct-P than in P-P-P, C-C-P, or B-B-P plots and tended to be lower in plots treated with aldicarb. Abundance of P. penetrans endospores was highest in the P-P-P plots, intermediate in the B-B-P rotations, lowest in all other rotations, and was unaffected by aldicarb. The high endospore densities in the P-P-P plots may have contributed to the uncharacteristically low nematode populations in the monoculture. Incidence of stem rot in peanut was lowest in treatments with flutolanil, intermediate in the control, and highest in treatments with aldicarb alone. The greater canopy cover in aldicarb-treated plots may have created a conducive environment for S. rolfsii infection.
Evidence for a Pythium sp. as a Chronic Yield Reducer in a Continuous Grain Sorghum Field
Authors: Davis M. A. , Bockus W. W.
Published: May 2007

Pythium spp. have been reported to reduce stands and cause stalk rot of grain sorghum. Evidence is presented that it also can cause a serious seed and root rot in the field under a continuous grain sorghum production system. Experiments were conducted for 4 years in a field that had been cropped continuously to grain sorghum for at least 10 years. Effects of seed treatments with captan and metalaxyl on plant stands, early to mid-season plant vigor, and grain yields were evaluated. In five field experiments, seed treatment with metalaxyl (73 g a.i./100 kg) increased grain yields by an average of 24.0% compared with nontreated seed. In three out of four field experiments, seed treatment with metalaxyl increased grain yields by an average of 13.1% above seed treated with captan (73 g a.i./100 kg). The yield increases could not always be explained in terms of differences among treatments in plant stands or in visual estimates of the amount of top growth 26 to 72 days after sowing. Apparently, the Pythium sp. causes a chronic root and seed rot that has a significant negative effect on grain production without necessarily affecting stands or early to mid-season growth. P. ultimum var. ultimum was the fungus most commonly isolated from roots and seeds collected from the field. Tests for Koch's postulates conducted in a greenhouse verified it as the causal organism. In the greenhouse, treatment with metalaxyl protected seeds and roots from attack by P. ultimum var. ultimum for at least 28 days after planting.
First Report of a Cucumber mosaic virus-Associated Satellite RNA in Lobelia erinus
Authors: Nameth S. G. P. , Fisher J. R.
Published: May 2007

Lobelia (Lobelia erinus L.) is a common herbaceous annual used in flower beds and hanging baskets. The plant blooms from early to late summer. In the summer of 2000, Lobelia plants expressing virus-like symptoms were collected from a greenhouse-based production site in Ohio. Affected plants expressed a mild leaf mosaic and stunting. Viral-associated dsRNA was isolated from 7 g of symptomatic leaf tissue (1). Four dsRNAs were observed at 3.9, 3.0, 2.25, and 1.05 kb indicating the presence of a Cucumovirus. A fifth dsRNA at 0.75 kb also was observed, consistent with the presence of a satellite RNA. Enzyme-linked immunosorbent assay (ELISA) analysis (Agdia, Inc., Elkhart, IN) of symptomatic Lobelia tissue confirmed the presence of Cucumber mosaic virus (CMV). A (S)CARNA-5 (-) cDNA clone (American Type Culture Collection #45124) was labeled with digoxygenin (DIG) as per the manufacturer's instructions (Genius II DIG-DNA Labeling Kit, Boehringer Mannheim) and used as a diagnostic probe to detect this satellite RNA. Northern hybridization confirmed the identity of the satellite RNA (2). This is the first report of any satellite RNA associated with a virus infection in Lobelia and the first report of CMV in this host in Ohio.

References: (1) J. R. Fisher and S. G. P. Nameth. HortScience 35:230–234, 2000. (2) R. A. Valverde et.al. Plant Dis. 74:255–258, 1990.
First Report of Aster Yellows-Related Subgroup I-A Phytoplasma Strains in Carrot, Phlox, Sea-Lavender, Aconitum, and Hyacinth in Lithuania
Authors: Valiunas D. , Alminaite A. , Staniulis J. , Jomantiene R. , Davis R. E.
Published: May 2007

Phytoplasma strains that belong to group 16SrI (aster yellows phytoplasma group), subgroup A (I-A, North American tomato big bud phytoplasma subgroup) were discovered in diverse plant species in Lithuania. Plants in which the strains were found exhibited symptoms characteristic of infections by phytoplasma. Carrot (Daucus sativus) with carrot proliferation disease exhibited symptoms of proliferation of the crown, chlorosis of young leaves, and reddening of mature leaves. Diseased phlox (Phlox paniculata) exhibited symptoms of virescence and leaf chlorosis. Diseased sea-lavender (Limonium sinuatum) exhibited abnormal proliferation of shoots, chlorosis of young leaves, reddening of mature leaves, and degeneration of flowers. Diseased hyacinth (Hyacinthus orientalis) exhibited chlorosis of leaves and undeveloped flowers. Diseased Aconitum sp. exhibited proliferation of shoots. Phytoplasma-characteristic ribosomal (r) DNA was detected in the plants by use of the polymerase chain reaction (PCR). The rDNA was amplified in PCR primed by primer pair P1/P7 and reamplified in nested PCR primed by primer pair R16F2n/R16R2 (F2n/R2), as previously described (1). The phytoplasmas were classified through restriction fragment length polymorphism (RFLP) analysis of 16S rDNA, amplified in the nested PCR primed by F2n/R2, using single endonuclease enzyme digestion with AluI, MseI, KpnI, HhaI, HaeIII, HpaI, HpaII, RsaI, HinfI, TaqI, and Sau3AI. Collective RFLP patterns indicated that all detected phytoplasma strains were affiliated with subgroup I-A. The 16S rDNA amplified from the phytoplasma (CarrP phytoplasma) in diseased carrot was cloned in Escherichia coli, sequenced, and the sequence deposited in the GenBank data library (GenBank accession no. AF291682). The 16S rDNAs of CarrP and tomato big bud (GenBank acc. no. AF222064) phytoplasmas shared 99.8% nucleotide sequence similarity. Phytoplasmas belonging to group 16SrIII (3), group 16SrV (D. Valiunas, unpublished data), and subgroup I-C in group 16SrI (2,3) occur in Lithuania. This report records the first finding of a subgroup I-A phytoplasma in the Baltic region and expands the known plant host range of this phytoplasma subgroup.

References: (1) R. Jomantiene et al. Int. J. Syst. Bacteriol. 48:269, 1998. (2) Jomantiene et al. Phytopathology 90:S39, 2000. (3) Staniulis et al. Plant Dis. 84:1061, 2000.
Effect of Silicon and Host Resistance on Sheath Blight Development in Rice
Authors: Rodrigues F. Á. , Datnoff L. E. , Korndörfer G. H. , Seebold K. W. , Rush M. C.
Published: May 2007

Rice cultivars high in partial resistance (Jasmine, LSBR-5), moderately susceptible (Drew and Kaybonnet), and susceptible (Lemont and Labelle) to sheath blight were grown in a silicon-deficient Histosol with and without calcium silicate slag. The treatment with silicon increased the concentration of this element in plant tissue by 80%over all experiments. Fertilization with silicon significantly reduced the severity of sheath blight, and the total area under the vertical lesion extension progress curve on moderately susceptible and susceptible cultivars compared to those cultivars high in partial resistance without silicon. The percentage of infected tillers was significantly reduced by 82, 42, 28, 41, 26, and 17%respectively for Jasmine, LSBR-5, Drew, Kaybonnet, Lemont, and Labelle, when silicon was applied, over all experiments. Dry matter accumulation was significantly greater with added silicon. In the absence of disease, silicon enhanced dry matter accumulation by 15%over the control, whereas silicon more than doubled the mean dry matter accumulation in infected plants. The application of silicon to complement host resistance to sheath blight appears to be an effective strategy for disease management in rice, especially when the soil is low or limiting in plant-available silicon.
Resistance of Wild Arachis Species to Late Leaf Spot and Rust in Greenhouse Trials
Authors: Pande S. , Rao J. Narayana
Published: May 2007

Seventy-four accessions of wild Arachis species along with a susceptible line TMV 2 belonging to A. hypogaea were evaluated for resistance to late leaf spot and rust under greenhouse environment. The experiment was conducted twice to confirm the resistance of the accessions. Percentage of leaf area damaged and disease score on a 1 to 9 scale for late leaf spot and rust were recorded for all accessions in both experiments. Additionally, percentage of defoliation was recorded for late leaf spot. One accession, ICG 8190, of A. hoehnei and one accession, ICG 13199, of A. duranensis were asymptomatic to late leaf spot in both experiments. In addition, 26 accessions were classified as resistant, 10 accessions were moderately resistant, and the remaining 36 accessions exhibited a susceptible reaction to late leaf spot. Only one accession, ICG 8954 of A. kuhlmannii, remained asymptomatic to rust in both experiments. All other accessions, except ICG 8206 of A. ipaensis, ICG 8197, ICG 8198, ICG 11549, and ICG 13178 of A. monticola, and ICG 13171 of A. stenosperma were classified as highly resistant to rust. Four accessions of A. monticola were susceptible to late leaf spot and rust.
Factors that Affect the Quality and Quantity of Sunlight Reflected from Alfalfa Canopies
Authors: Guan J. , Nutter F. W.
Published: May 2007

Experiments were conducted from 1997 to 2000 in Ames and Nashua, IA, to quantify the effects of incident radiation, sun angle, leaf wetness, and sensor height on the quality and quantity of sunlight reflected from alfalfa canopies using a hand-held, multispectral radiometer. Incident radiation had negligible effects on the percentage of sunlight reflected from alfalfa canopies in the visible wavelength bands (460 to 710 nm) and significant negative effects on the percentage of sunlight reflected from alfalfa canopies in the near-infrared wavelength bands (760 and 810 nm). Percentage reflectance values (810 nm) decreased between 0.20 and 0.32% for each 100 watts m-2 increase in incident radiation. Percentage reflectance values in all wavelength bands obtained prior to 1100 h and after 1500 h CST were significantly higher than reflectance measurements obtained between 1100 h and 1500 h. The presence of moisture on leaves (leaf wetness) significantly increased percentage reflectance for all wavelength bands. Sensor height had variable effects on percentage reflectance in all wavelength bands. This variability was most likely due to changes in the heterogeneity of alfalfa canopies with increasing sensor height. In experiments conducted with more homogenous canopies (oat and turfgrass), sensor height had no significant effect on the percentage of sunlight reflected from these canopies. To minimize the effects of all of the above nondisease factors on the measurement of percentage of sunlight reflected from crop canopies, we recommend that percentage reflectance measurements be obtained between 1100 and 1500 h when plant canopies are dry, with a constant sensor height (sampling unit area), and within a small range of incident radiation for all measurements.
Comparison of Three Fungicide Spray Advisories for Lettuce Downy Mildew
Authors: Wu B. M. , Subbarao K. V. , van Bruggen A. H. C. , Koike S. T.
Published: May 2007

Lettuce growers in coastal California have relied mainly on protective fungicide sprays to control downy mildew. Thus, timing of sprays before infection is critical for optimal results. A leaf-wetness-driven, infection-based advisory system, previously developed, did not always perform satisfactorily. In this study, the advisory system was modified by incorporating a pathogen survival component (system 1) or both survival and sporulation components (system 2). These systems were then evaluated in commercial lettuce fields in coastal California during 1996-1998. Three or four treatments were carried out in each field: (i) no spray; (ii) sprays as scheduled by the growers; (iii) sprays following modified system 1; and (iv) sprays following the original advisory system (1996) or modified system 2 (1998). Downy mildew incidence was evaluated every 2 to 9 days. In fields with drip irrigation, the number of fungicide applications was reduced by one or two regardless of the advisory system used compared to the grower's calendar-based schedule, although one unnecessary spray was recommended in 1996 at Soledad and 1997 at Salinas. Under all three systems, disease levels were low (incidence <25% and about 1 lesion per plant) for fields with drip irrigation, but not for fields with sprinklers (incidence up to 100% and 5 to 10 lesions per plant). For the first time, we established that survival and sporulation components are not needed for a lettuce downy mildew forecasting system. Instead, a threshold with a shorter period of morning leaf wetness and high temperatures were found to have potential for improving forecasting efficiency.
Survey Methods for Assessment of Citrus tristeza virus Incidence in Citrus Nurseries
Authors: Hughes G. , Gottwald T. R.
Published: May 2007

Monitoring of plant health takes place in citrus nurseries to prevent the distribution of infected plants to commercial groves. In this article, both analytical and simulation methods are used to characterize schemes by which such monitoring may be carried out, in the particular context of Citrus tristeza virus infection. Two aspects of such schemes are discussed in detail. The inclusiveness of a sample is an assessment of the degree of redundancy that occurs because, in some samples, the progeny of identically infected propagation material may appear more than once. The operating characteristic function shows the probability of reaching a decision, based on sampling, that a population of daughter plants has an incidence of infection less than or equal to some adopted threshold level for any actual level of incidence in the population. If the same proportion of the population is assessed at different population sizes, both the inclusiveness and the operating characteristic function vary with population size. However, sample sizes may be calculated so that a specified operating characteristic function is maintained as population size varies. The sample sizes required to meet the conditions specified on the operating characteristics do not increase proportionally with population size. Under such a scheme, fewer samples might need to be taken from large populations of daughter plants than would be the case if a constant percentage sampling scheme were adopted.
First Report of Beech Bark Disease in Michigan
Authors: O'Brien J. G. , Ostry M. E. , Mielke M. E. , Mech R. , Heyd R. L. , McCullough D. G.
Published: May 2007

Beech bark disease of American beech (Fagus grandifolia) is caused by the interaction of an introduced scale insect (Cryptococcus fagisuga) and the native fungus Nectria galligena, or N. coccinea var. faginata, which is thought to be introduced. Infestations of the insect precede development of the disease, and N. galligena is often found before N. coccinea var. faginata. Previously published records indicate that the beech scale extends as far west as eastern Ohio (2) and southern Ontario (Sajan, personal communication). The scale is now well established in several locations in both the Upper Peninsula (UP) and Lower Peninsula (LP) of Michigan. The scale insect has been found in beech stands throughout three counties (Oceana, Mason, and Muskegon) along the Lake Michigan shore in the LP, extending for at least 100 km from north to south, and occurring up to about 80 km inland. In the eastern UP, beech scale has been found in four counties (Alger, Chippewa, Luce, and Schoolcraft). The heaviest beech scale infestations are distributed around Ludington State Park in the west central LP and the Bass Lake Forest Campground in the eastern UP. The extent of the insect infestation suggests that it has been present in Michigan for many years, with anecdotal accounts placing the first observations of beech scale at Ludington State Park around 1990. These infection centers are distant from previously known beech scale infestations and are located in heavily used recreation areas, suggesting that the insect may have been transported by human activity. Perithecia of N. coccinea var. faginata were found in Ludington State Park in the LP at N 44° 1.951', W 86° 29.956' and perithecia of N. galligena were found at the Bass Lake site in the UP, at N 46° 27.748', W 85° 42.478'. The identity of the fungi collected from each location was confirmed by measurements of perithecium and ascospore morphology (1). Perithecia at both sites were scarce and difficult to find. Surveys planned for the summer and fall of 2001 will further delimit the occurrence and distribution of the pathogens involved in the disease in Michigan. To our knowledge, this is the first report of the beech scale and beech bark disease in Michigan, with N. galligena and N. coccinea var. faginata identified as the pathogens.

References: (1) H. V. T. Cotter and R. O. Blanchard. Plant Dis. 65:332–334, 1981. (2) M. E. Mielke et al. Plant Dis. 69:905, 1985.