摘要:

AbstractSheath brown rot of rice caused byPseudomonas fuscovaginaehas been described in areas where low temperatures occur during the rice booting and heading stages. To analyse the relationship between pathogenicity ofP. fuscovaginaeand low temperatures, pathogenicity process in rice at booting stage was studied in a growth chamber at midrange and low temperatures. Analysis performed at 13°C, 18°C and 23°C in two rice cultivars showed that pathogenicity ofP. fuscovaginaewas explained by the general model of the independent action. The inoculum dose necessary to obtain 50% of diseased sheaths decreased with increase of temperature Analysis ofplantabacterial population dynamics and mean response time pointed out that low temperatures affected pathogen multiplication in host before and after symptoms development. In consideration of our results, it was concluded that low temperatures acted negatively on the pathogenicity process ofP. fuscovaginae.Therefore, occurrence ofP. fuscovaginaein areas where rice cultivation is restricted by low temperatures can not be explained by a direct effect of temperatures on pathogenici

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00318.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractTo determine the association between visual disease severity and deoxynivalenol (DON) concentration inFusarium graminearumsilk‐inoculated maize ears, 23 Ontario hybrids were assessed in 1989, 1991, 1992, and 1993. The relationship was exponential and consistent between years. Ears with more than 25% of the kernels visibly infected could have very high concentrations of DON. Both temperature and rainfall in July and August influence the level of disease severity and the subsequent DON accumulation. Visual disease severity ratings should be sufficient for the selection of more resistant genotypes in corn improvement programs during routine screenings. Thus, mycotoxin analyses can be reserved for initial selection of parental material and final verification of developed inbreds or hybrids. No relationship was found between hybrid maturity and disease severity or DON concentratio

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00319.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractBacterial speck symptoms on leaves of the tomato cultivar Erminia Fl (Petoseed), heterozygous for thePtoresistant gene, were observed in June 1995 in Northern Italy. Using individual‐lesion isolation, 8 bacterial isolates were obtained from the affected leaves, which were identified asPseudomonas syringaepv.tomatoby biochemical, physiological, nutritional and pathogenicity tests. When the differential cultivar Ontario 7710, homozygous for the Pto gene, was inoculated with the bacterial isolates, 4 of them provoked the typical bacterial speck symptoms and therefore belonged to race 1. This is the first occurrence ofP. syringaepv.tomatorace 1 in Italy and the first time this race has been isolated on aPtogene‐bearing tomato cultivar grown in open fi

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00320.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe amounts of the polyacetylenes falcarindiol (heptadeca‐1, 9(Z)‐dien‐4,6‐diyn‐ 3,8‐diol) and falcarinol (heptadeca‐1,9(Z)‐dien‐4,6‐diyn‐3‐ol) were determined in the roots of a number of commercial carrot cultivars in order to study their influence on resistance to storage rots caused by three different fungi. The content of the diol was much higher in periderm/pericyclic parenchyma than in phloem parenchyma and the outer tissues were less susceptible toMycocentrospora acerinathan the inner tissues. A strong and significant negative relationship was found between falcarindiol contents in the periderm/pericyclic parenchyma and susceptibility toMycocentrospora acerinafor 14 of the 16 cultivars tested. The relationship was less noticable forSclerotinia sclerotiorumand not significant

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00321.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstractβ‐1,3‐glucanase and chitinase activities were induced locally and systemically 4–25 and 11–25 days, respectively, after spraying the surface of the third pair of coffee leaves from the apex of 8‐month‐old plants with a 50 mg/ml aqueous suspension ofBacillus thuringiensisin a commercial formulation (Thuricide HP‐Sandoz). The treatment also induced local and systemic resistance againstHemileia vastatrixafter the application of the inducer. Within 14–18 days of application of the Thuricide inducer, the β‐1,3‐glucanase activity in the locally and systemically‐protected unchallenged leaves reached maximum levels of 226% and 279% higher levels respectively, than in control plants. The chitinase activity reached maximum levels of 224% and 181% respectively, within 18–21 days after treatment with the inducer. Two β‐1,3‐glucanase bands were detected by native PAGE electrophoresis in extracts from locally‐and systemicallyprot

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00322.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractInduction of resistance to crown rust, caused by Puccinia coronata Cda. var, avenae Frazer et Led., occurred in seedlings of three genetic lines of oats (Avena sativa L.) inoculated sequentially with one of three inducer‐challenger combinations of the pathogen. There was significant reduction in both the number of pustules per leaf and the weight of urediospores harvested in all three host genotypes tested. There were highly significant differences between individual spore harvests correlated with age of the pustules. Development of telia by the challenger was found to occur considerably later, and was less intense, when the challenger was inoculated alone in contrast to treatments in which the challenger followed pre‐inoculation with the inducer. There was no correlation between the numbers of resistant and susceptible lesions within the range of inoculum density used in these experime

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00323.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractDetection of the bacterial ring pot pathogen (Clavibacter michiganensissubsp.spedonicus) in seed potato lots by laboratory indexing complements visual inspection. The probability of detecting symptomless infections is a function of sample size and incidence of infection. We determined the incidence of asymptomatic stem and tuber infections in four potato cultivars at three levels of inoculum. At the high inoculum level, 51–93% of stems were infected at 80 days after planting, and 10–59% of the tubers were infected at harvest. The effect of the different percentages of infected stems and tubers on the probability of detection for simple random sampling was calculated for a constant sample size. The actual detection levels for two cultivars planted in field plots with predetermined incidence levels of ring rot infected plants were reasonably close to predicted probabilit

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00324.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA bioassay system was developed for studying thein vitroreaction of sunflower (Helianthus annuusL. cv. ‘Nanus’) against the toxin produced by the virulent pathotype IMI 366417 (1) of the pathogenic fungusAlternaria alternata.Cotyledons from 2‐week‐old seedlings were cultured on a MS (Murashige and Skoog) medium supplemented with 0.3 μM NAA (α‐napthylacetic acid) and 1.3 μM BA (6‐benzyladenine). Exponentially growing calli were transferred to selective media containing toxin solutions at various concentrations. The fresh weight of the cultured calli was reduced as the toxin concentration increased, although the viability of the cells, expressed as callus dehydrogenase activity, increased. Selection for toxinresistant genotypes was attempted at 30% toxin concentration, which causes a 90% reduction in callus growth. After one month in culture, 18% of the calli demonstrated resistance to the toxin. However, no plants could be regenerated from those calli after transfer onto a MS medium supplemented with 5.4 μM NAA and 4.4 μM BA. The effect of the toxin purification method on toxin yield and biological activity, as well as its possible mode of cellular action are discussed. The results of these experiments may contribute to a better understanding of the disease mechanism and help establish an efficient selection method of resistant sun

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00325.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractA leaf spot disease of mango (Mangifera indica) caused byCylindrocladium scopariumwas found in central Brazil in 1994. Pathogenicity tests and re‐isolations from artificially‐inoculated leaves confirmed that C.scopariumwas the incitant. This is believed to be the first report of the fungus attacking mango lea

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00326.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractChina‐tree or paraiso (Melia azedarach) decline, caused by a phytoplasma, is a disease in Argentina for which hitherto no diagnostic reagents were available. The production of a polyclonal antiserum using a purification protocol involving a double Percoll gradient is reported. The antiserum was used successfully in immuno‐dot blot assay to discriminate between infected and healthy plants. It also recognized, although less reliably, other phytoplasmas present in garlic (Allium sativum), peach (Prunus persica) and tona (Tona cilliata). Organisms that by their size and morphology resembled phytoplasmas were detected by immuno‐electron microscopy and immunogold labelling. The ability of the antiserum to discriminate between healthy and infected plants was confirmed by PCR amplification of fragments only from infected p

ISSN:0931-1785    

DOI:10.1111/j.1439-0434.1996.tb00327.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY