bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclamen (Cyclamen persicum L.): a dead‐end host species for 16Sr‐IB and ‐IC subgroup phytoplasmas
Authors: ALMA A , MARZACHÌ C , D'AQUILIO M , BOSCO D 
Published: July 2006

SummaryPhytoplasmas belonging to the 16S rDNA subgroups IB and IC were found in five cyclamen (Cyclamen persicum L.) plants showing virescence and yellow stunted leaves and one plant showing phyllody, rolled and thickened leaves, respectively. Two cyclamens, representing the two syndromes, were chosen as source plants for transmission trials in which three leafhopper species, known as vectors of IB and IC subgroup phytoplasmas, were used to inoculate cyclamen and periwinkle [Catharanthus roseus (L.) G. Don] test plants. Out of 366 tested plants only one periwinkle exposed to Euscelis incisus was found harbouring a 16Sr‐IB phytoplasma. Out of 60 tested vector insects, only one adult of Macrosteles quadripunctulatus and two of E. incisus fed on 16Sr‐IB source cyclamen gave a positive amplification signal in nested PCR. This extremely low level of transmission to both cyclamen and the very susceptible periwinkle strongly suggests that cyclamen, commonly found infected in crops, is an unsuitable species for phytoplasma acquisition and can be regarded as a dead‐end host plant for phytoplasmas belonging to both IB and IC subgroups. Indications for glasshouse management are drawn from these findings. Among the leafhoppers investigated E. incisus falls most under suspicion since it feeds better than the others on cyclamen, was able to transmit the disease to one periwinkle plant, and IB phytoplasmas were detected in two individuals.
Effects of diseases on the growth and yield of spring linseed (Linum usitatissimum), 1988–1998
Authors: PERRYMAN S A M , FITT B D L 
Published: July 2006

SummaryIn spring linseed field experiments with fungicides at Rothamsted from 1988 to 1998, substantial yield losses assoeiated with diseases occurred in three years and slight losses could be associated with diseases in other years. These yield losses were related to decreases in yield components (thousand grain weights and number of capsules). Leaf browning was observed each year and percentage leaf area with browning was the disease factor most consistently related to yield losses (in five years). Yield loss relationships for these five years suggested that for each 10% increase in percentage leaf area with browning there was a yield loss of 0.10 to 0.18 t ha−1. Stem browning, lesions on capsules and powdery mildew were associated with yield losses in two years, three years and one year, respectively. Yield losses were greatest in years when the period of flowering and early capsule development in June and July was wetter than average; the predominant disease was grey mould (Botrytis cinerea) in wet years up to 1996, whereas pasmo (Mycosphaerella linicola) was most important in 1997 and 1998. Observed yield losses were small in hot, dry years when powdery mildew (Sphaerotheca lini) and verticillium (Verticillium dahliae) were the predominant diseases.
Oligogenic inheritance for resistance to Zucchini yellow mosaic virus in Cucurbita pepo
Authors: PARIS H S , COHEN S 
Published: July 2006

Summary‘True French’ is an open‐pollinated cultivar of the Zucchini (Courgette) Group of Cucurbita pepo and is susceptible to Zucchini yellow mosaic virus (ZYMV). Using C. moschata‘Menina’ as the source of ZYMV resistance and following six generations of backcrossing, a true‐breeding line nearly isogenic to ‘True French’, designated 381e, was recovered that carried ZYMV resistance, albeit not at as high a level as in ‘Menina’. ‘True French’ and accession 381e were crossed, and their reciprocal F1, F2, and backcross progenies were grown in a chamber and inoculated with a highly virulent, non‐aphid‐transmissible strain of ZYMV. Nearly all F1 plants and all plants of the backcross to 381e were classified as resistant. Segregation to resistant and susceptible individuals occurred in the backcross to the susceptible parent, in accordance with a 3:5 three‐gene ratio of resistant: susceptible. The F2 segregated in accordance with a ratio of 45 resistant : 19 susceptible, which would be obtained if there was one major gene for resistance, Zym‐1 (Zym), and two other genes, herein designated Zym‐2 and Zym‐3, both of which for complementary to Zym‐1. The presence of Zym‐1 and either Zym‐2 or Zym‐3 is necessary for resistance to be expressed in young plants, but the presence of all three might be necessary for resistance to continue to be expressed during subsequent development of the plants. Evidently, Zym‐2 and Zym‐3 are ubiquitous in C. moschata but their susceptible alleles are much more common in C. pepo. As the level of resistance of 381e to ZYMV is not as high as that of C. moschata‘Menina’, additional, as yet unidentified, genes must be involved in conferring high resistance to this virus.
Effect of potato used as a trap crop on potato cyst nematodes and other soil pathogens and on the growth of a subsequent main potato crop
Authors: SCHOLTE K 
Published: July 2006

SummaryA field experiment in which main‐crop potatoes were grown every other year was conducted on a sandy soil from 1994 to 1999. The aim of the experiment was to control soil‐borne pathogens of potato with ecologically sound methods. Potato grown as a trap crop from the end of April to the end of June (8 wk) was used to control potato cyst nematodes (PCN) (Globodera pallida), and its effects on other important soil pathogens and on the growth of a subsequent potato crop were also assessed. Additional experimental treatments were a potato crop from which the haulm was removed and a green manure crop. Three potato cultivars with different degrees of resistance to PCN were grown as the main crop. Duplicate sets of the experiment were run concurrently.The PCN were effectively controlled by the potato trap crop. When a highly resistant potato cultivar was grown as a main crop after the trap crop, the post‐harvest soil infestation was very low. When a moderately resistant cultivar was grown after the trap crop the soil infestation also remained low. When the trap crop was alternated with a susceptible potato cultivar as a main crop, soil infestation increased slightly, but the degree of control when compared with no trap crop averaged 96%.Soil infestation with root‐knot nematodes (mainly Meloidogyne hapla) increased when potato was grown as a trap crop, but soil infestation with the root‐lesion nematode Pratylenchus crenatus was not affected. Stem canker caused by Rhizoctonia solani was not affected by the trap crop but black scurf (sclerotia of R. solani) on tubers was reduced. Soil infestation with Verticillium dahliae declined in one of the duplicate sets of the experiment but not in the other. However, stem infections by V. dahliae were significantly decreased in both sets, although the effect depended on the PCN‐resistance level of the potato cultivar. When a highly resistant potato cultivar was grown Verticillium stem infections were not significantly affected, they were decreased with a moderately resistant cultivar but the decrease was most pronounced with a PCN‐susceptible cultivar.Senescence of a following potato crop was not influenced by the trap crop when a highly PCN‐resistant cultivar was grown, but it was delayed in the case of a moderately resistant or a susceptible cultivar, resulting in higher tuber yields for those cultivars.The experiment proved that a trap crop can be an alternative to chemical soil disinfection but, for several reasons, the potato itself is not an ideal crop for this purpose; a trap crop other than potato must be developed.
Genotypic variation in ‘early warning signals’ from roots in drying soil: intrinsic differences in ABA synthesising capacity rather than root density determines total ABA ‘message’ in cowpea (Vigna unguiculata L.)
Authors: KULKARNI M J , PRASAD T G , SASHIDHAR V R 
Published: July 2006

SummaryIn a comparison of six cowpea cultivars, we determined the variation in abscisic acid (ABA) production as an ‘early warning signal’ produced in response to drought stress. By imposing drought only to the upper 20 cm rooting zone, we compared the rates of ABA synthesis relative to (i) total root mass and (ii) inherent variation per unit root mass. We were able to relate the intensity of the stress response to these two factors, and determine which is quantitatively more important as the primary signal indicating responsiveness to drought stress. Plants were grown in 1.2 m long columns and a soil drying treatment imposed in such a way that that upper roots were in dry soil and deep roots in soil at field capacity. Relative water contents (RWC) of stressed plants were similar and not significantly different from those of well watered controls. However, roots accumulated ABA in the dehydrated zone, where root water content ranged from 10–12 g g−1 DW. The soil moisture contents and root ‐water contents in the dry zone were similar for each of the different varieties. However, the ABA contents were significantly different in drought‐stressed (upper) roots and ranged from 7.82 nmol g−1 DW in cv. APC 689 to 16.02 nmol g−1 DW in cv. APC 370, such that for varieties with similar overall root weights (e.g. APC 580 and APC 540) the different ABA contents were related to the capacity for ABA synthesis. The relationship between stomatal conductance and total root ABA was assessed, with a negative relation (r= 0.90, n= 24, P= 0.05) suggesting that the intrinsic capacity of cowpea varieties for ABA synthesis could play an important role in regulating stomatal conductance in a drying soil and provide useful selection criteria for tolerance to drought stress.
Effect of soil type, salinity, and allelochemicals on germination and seedling growth of a medicinal plant Lepidium sativum L.
Authors: EL‐DARIER S M , YOUSSEF R S 
Published: July 2006

SummaryThe present work was conducted to elucidate the effect of soil type, salinity stress and allelochemicals from alfalfa on the germination efficiency, seedling growth and photosynthetic pigments of Medicago sativa L. The highest germination rate (69.9%) was recorded for seeds cultivated in sandy soil followed by that of clay soil (42%) and then loamy soil (19%).The maximum germination rate was attained at 50 mM NaCl concentration level, after that the values were decreased as the salinity levels increased. The maximum lengths (cm) of plumule and radicle and their growth rates (cm/day) were obtained at control level and found to decline significantly as the salinity increased.Aqueous extracts of alfalfa reduced the germination rate, radicle and plumule growth and seedling dry weight of L. sativum. However, chlorophyll and carotenoid content was increased, their maxima were recorded at 50% concentration level. The chlorophyll a/b ratio attained its maximum at the full strength concentration level.
Effects of potassium carbonate as an alternative de‐icer on ground vegetation and soil
Authors: ERHART E , HARTL W 
Published: July 2006

SummaryThe effects of the new de‐icer potassium carbonate on the growth and species composition of a mixed sward and on the pH and electrical conductivity of the soil were examined in a four‐year field trial and compared with sodium chloride. There were small positive effects of K2CO3 on the biomass yield of the sward at application rates up to 200 g m−2 yr−1, while effects were less negative than those of NaCl at annual application rates of 200 – 400 g m−2 yr−1. The species composition of the sward changed considerably with K2CO3 application, Agropyron repens becoming the dominant species. The pH was elevated slightly more by K2CO3 than by NaCl application. Electrical conductivity as an index of soil salinity was increased by both de‐icers. K2CO3 was more adsorbed to soil colloids than NaCl, so that the rise in E.C. resulting from application of the former was restricted to the uppermost 10 cm of soil.
Impact of a disease and a defoliating insect on houndstongue (Cynoglossum officinale) growth: implications for weed biological control
Authors: CONNER R L , DECLERCK‐FLOATE R A , LEGGETT F L , BISSETT J D , KOZUB G C 
Published: July 2006

SummaryThe noxious weed houndstongue (Cynoglossum officinale) has become a major problem on the forested rangelands in the interior of British Columbia. However, recently the fungus Phoma pomorum and the ranchman's tigermoth (Platyprepia virginalis) were identified as potential biocontrol agents of this biennial weed. Infection by the fungus Ph. pomorum resulted in the formation of large brown lesions on leaves of houndstongue. In culture, the fungus readily produced pycnidia with pycnidiospores measuring 5.7 μm × 1.7 μm. The effect of Ph. pomorum and P. virginalis on the growth of houndstongue was examined over a six week period. Leaf age strongly influenced the intra plant distribution of insect feeding and lesion formation with Ph. pomorum primarily attacking the older leaves, while P. virginalis larvae preferred feeding on young leaves. Infection of leaves by Ph. pomorum resulted in their premature death. The effect of infection by Ph. pomorum on plant weight varied among tests, but the disease usually increased the number or percentage of dead leaves and reduced root biomass. A study of the effect of plant age and disease on houndstongue showed that younger plants infected with Ph. pomorum had a slightly higher percentage of dead leaves than older plants, but that reductions in live leaf weight and root weight were similar for different age groups. Six weeks after exposure to feeding damage by P. virginalis, there was no significant effect of P. virginalis on plant weight either acting alone or in combination with Ph. pomorum.
Responses of the sweetpotato whitefly, Bemisia tabaci, to the chinaberry tree (Melia azedarach L.) and its extracts
Authors: HAMMAD E M ABOU‐FAKHR , NEMER N M , HAWI Z K , HANNA L T 
Published: July 2006

SummaryHost preference bioassays for adults of the sweetpotato whitefly were performed with leaves of the chinaberry tree Melia azedarach L., tomato, cucumber and bean. Fruit and leaf extracts of the chinaberry tree were tested against adults of the sweetpotato whitefly. Fruit extracts were tested against eggs, first and second instar nymphs, and pupae of the insect. Treatments included aqueous, methanol, and acetone fruit extracts of 200 mg ml−1 and serial dilutions of 20.0 and 2.00 mg ml−1, ether extract, the botanical insecticides Azatin® and Margosan® ‐O and the control, water or water with Triton®. Mortality data was collected at 6, 7, and 8 days after treatment of the eggs, nymphs and pupae, respectively. Results of the host preference bioassays indicated a significantly lower number of live insects on leaves of the chinaberry tree vs leaves of bean, cucumber, and tomato after 24 h. This indicates that M. azedarach is not a good host for the sweetpotato whitefly. Adults of the insect were significantly more repelled from tomato plants treated with the undiluted extracts when compared to the control after 72 h. There were significant differences in percent mortality of nymphal instars when exposed to the undiluted extracts compared to other extracts and the control. However, there was no significant effect of the fruit extracts on the egg and pupa instars. Thus M. azedarach extracts were found to be repellent to the whitefly adults, while the fruit extracts have shown a significant detrimental effect against early nymphal instars. In general, the methanol extracts were more active against B. tabaci than extracts with other solvents.
Effects of foliar sprays of azoxystrobin on take‐all in wheat
Authors: JENKYN J F , BATEMAN G L , GUTTERIDGE R J , EDWARDS S G 
Published: July 2006

SummaryAverage percentages of winter wheat plants with severe take‐all were decreased by up to half by azoxystrobin applied as foliar sprays in four field experiments. Decreased take‐all in three of the experiments was associated with increased grain yield but effects on other diseases may have contributed to these responses. Standard fungicide sprays were ineffective. The effects differed, but not consistently, among different cultivars that were tested in three of the experiments. One, two or three sprays of azoxystrobin or kresoxim‐methyl, in autumn, spring or summer, were tested in the fourth experiment. Unlike azoxystrobin, kresoxim‐methyl had no consistent effects but a smaller amount was applied. Two or three sprays of azoxystrobin were more effective than a single spray but their timing was unimportant. Such control of a root disease by a foliar‐applied fungicide is unusual but may help to explain some of the unexpectedly large yield responses to azoxystrobin that have been reported. This relatively broad‐spectrum fungicide may have the potential to contribute to the practical management of take‐all but further research is needed to determine how best to exploit its effects consistently.
Relationships between phoma leaf spot and development of stem canker (Leptosphaeria maculans) on winter oilseed rape (Brassica napus) in southern England
Authors: SUN P , FITT B D L , GLADDERS P , WELHAM S J 
Published: July 2006

SummaryModels were constructed to describe the relationships between incidence of phoma leaf spot at different growth stages in autumn/winter or early spring and incidence of stem canker (basal canker or stem lesions) in summer on winter oilseed rape in southern England. Model 1, describing the phoma leaf spot/basal canker relationship, wasy1=β0+β1x1+β2(x2‐x1) ifx2>x1, andy1=β0+β1x1ifx2≤x1, in whichy1was the incidence (% plants affected) of basal canker at harvest,x1was the maximum incidence of phoma leaf spot during the period from sowing to growth stage (G.S.) 1,6‐1,7 (about 100 days after sowing) andx2was the maximum incidence of phoma leaf spot between G.S. 1,7 and G.S. 2,0 (start of stem extension). Model 2, describing the phoma leaf spot/stem lesion relationship, wasy2=α0+α1x3+α2x4, in whichy2was the incidence of stem lesions at harvest,x3was the incidence of phoma leaf spot at G.S. 3,3–3,5 (flower buds visible) andx4was the incidence of phoma leaf spot at G.S. 4,5–5,5 (flower buds opening). Data from field experiments with four winter oilseed rape cultivars at Boxworth or Rothamsted in the 1992/93, 1993/94, 1996/97, 1997/98 or 1998/99 seasons were used to test the models. The values ofR2for the regression equations testing model 1 for the phoma leaf spot/basal canker relationship were 0.75, 0.93, 0.91 and 0.89 for cvs Apex, Bristol, Capitol and Envol, respectively. The values ofR2for the regression equations testing model 2 for the phoma leaf spot/stem lesion relationship were 0.58, 0.57, 0.54 and 0.71 for cvs Apex, Bristol, Capitol and Envol, respectively. The phoma leaf spot/basal canker relationship (model 1) could also be fitted to the combined data set for all four cultivars (R2= 0.65), whereas the phoma leaf spot/stem lesion relationship (model 2) could not to be fitted to the combined data set for the four cultivars. The relationships between incidence and severity of stem canker were examined and the values ofR2for the regressions of severity on incidence were 0.91 for basal canker and 0.89 for stem lesions.
Identification of resistance to Peanut bud necrosis virus (PBNV) in wild Arachis germplasm
Authors: REDDY A S , REDDY L J , MALLIKARJUNA NALINI , ABDURAHMAN M D , REDDY Y V , BRAMEL P J , REDDY D V R 
Published: July 2006

SummaryEighty three wild Arachis germplasm accessions, belonging to 24 species of five sections and one natural hybrid derivative of a cross between the cultivated and a wild Arachis species, were evaluated along with a susceptible groundnut cultivar for resistance to Peanut bud necrosis virus (PBNV) in a replicated field trial at ICRISAT, Patancheru, India. Thirty days after sowing, the percentage of infected plants were recorded for all the accessions and subsequently young leaflets from all these accessions were tested for the presence of the virus by enzyme linked immunosorbent assay (ELISA). One accession each of A. benensis and A. cardenasii, and two accessions of A. villosa, in the section Arachis, two accessions of A. appressipila in the section Procumbentes, and one accession of A. triseminata under section Triseminatae were not infected by PBNV. These seven field‐resistant accessions were tested under glasshouse conditions for virus resistance by mechanical sap inoculations. One accession of A. cardenasii and two accessions of A. villosa did not show systemic infection. Similarly, in another glasshouse test, where 13 A. cardenasii accessions of section Arachis were evaluated, two accessions did not show systemic infection. In all these resistant accessions, the inoculated leaves showed infection, but the systemic leaves did not show the presence of virus in spite of repeated mechanical sap inoculations. So, the resistance in these accessions appears to be due to a block in systemic movement of the virus. To our knowledge this is the first report on the identification of resistance to PBNV in wild Arachis species. Since both A. cardenasii and A. villosa are the progenitors of cultivated groundnut and can be hybridised with the latter, the resistant accessions are being utilised in conventional breeding programmes to transfer PBNV resistance to widely adapted groundnut cultivars.
Pathogenicity of fungi associated with melon vine decline and selection strategies for breeding resistant cultivars
Authors: IGLESIAS A , PICÓ B , NUEZ F 
Published: July 2006

SummaryMelone Vine Decline is a severe rot root disease of increasing world‐wide importance. In Eastern Spain it is related to the presence ofAcremonium cucurbitacearumandMonosporascus cannonballus. The strong influence of environmental conditions on the progress of this disease has made its study difficult. A field screening ofCucumis meloaccessions has been conducted over four years. Simultaneously, the pathogenicity of isolates of the two fungi recovered from the screening field was studied. These were more aggressive than other Spanish and American isolates. Percentage of vine decay was scored, togeter with root damage, the latter being evaluated by using four scoring systems based on root characteristics and disease severity. Root inspection alowed the selection of resistance sources, even when aboveground symptoms did not appear, due to the lack of environmental stresses at time of fruit maturity. The root damage scoring if environmental stresses occur during fruit maturity.The accessionC. melovar.agrestisPat 81 consistently exhibited high field resistance level, expressed as a higher percentage of symptomeless plants, together with a significant delay in symptoms appearance. The F1hybrids derived from the cross Pat 81 ×C. melosusceptible varienties showed an intermediate level of resistance between the parents, suggesting a partial dominance gene action. The high resistance level found in Pat 81, and also in its derived hybrids, against the aggressive isolates found in this area, makes it promissing for breeding melon verieties resistant to melon vine decline.