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Soybean rust, Phakopsora pachyrhizi, has been considered a threat to the production of the U.S. soybean, Glycine max. During the past decade, this disease gradually spread to Africa, South America, and recently to the United States. Previous soybean rust risk assessments with an assumption of availability of spores early in a season showed that weather conditions (dew and temperature) during a growing season, in general, are suitable for disease development in U.S. soybean-growing regions. Predicting the time of rust appearance in a field is critical to determining the destructive potential of rusts, including soybean rust. In this study, comparative epidemiology was used to assess likely rust incipient time in four locations within the U.S. Soybean Belt from south to north: Baton Rouge, LA; Charlotte, NC; Indianapolis, IN; and Minneapolis, MN. Temperature effects on the infection cycle of five rusts occurring in the Midwest were evaluated using a general disease model. The likely incipient times were examined with the modeling results. Among the rusts studied, early-appearing rusts had suitable conditions for development earlier in a season. However, a lag period of several weeks to more than 3 months was found from the time when conditions are suitable for a rust to develop or when hosts are available to the time when the rust was detected in fields. Length of the lag period differed among the rust species examined. If nature of long-distance dispersal is not significantly different among the rusts, implications of our study to the expected seasonal soybean rust incipience in fields lead to two possible scenarios: (i) average appearance time of soybean rust across the Soybean Belt should be somewhere between appearance times of common corn rust and southern corn rust, and (ii) with late appearance of the disease, late-planted soybean in the south has greater risk. [ABSTRACT FROM AUTHOR]

Sixty-four isolates of Colletotrichum gloeosporioides were isolated from infected Limonium spp. cultivated in 12 different locations in Israel. All isolates were identified as belonging to the C. gloeosporioides complex by species-specific primers. Of these isolates, 46 were resistant to benomyl at 10 μg/ml and 18 were sensitive to this concentration of fungicide. Based on arbitrarily primed polymerase chain reaction of all isolates and internal transcribed spacer-1 sequence analyses of 12 selected isolates, the benomyl-resistant and -sensitive populations belong to two distinct genotypes. Sequence analyses of the β-tubulin genes, TUB1 and TUB2, of five sensitive and five resistant representative isolates of C. gloeosporioides from Limonium spp. revealed that the benomyl-resistant isolates had an alanine substitute instead of a glutamic acid at position 198 in TUB2. All data suggest that the resistant and sensitive genotypes are two independent and separate populations. Because all Limonium plant propagation material is imported from various geographic regions worldwide, and benomyl is not applied to this crop or for the control of Colletotrichum spp. in Israel, it is presumed that plants are bearing quiescent infections from the points of origin prior to arrival. [ABSTRACT FROM AUTHOR]

Gray mold, caused by Botrytis cinerea, severely affects the base of the stems of lisianthus (Eustoma grandiflorum) plants as well as the cut stems left after flowers are harvested. This study examined infection of lisianthus plants by B. cinerea under laboratory and commercial greenhouse production conditions typical for Israel and evaluated cultural methods for manipulating disease development in commercial greenhouses. Although the lower nodes of lisianthus stems are typically infected, in this study, the inherent susceptibility of these nodes was less than that of nodes midway up the stem. Greater light intensity (4,860 lux) was associated with significantly more severe stem wounds than lower light intensities of 140 to 1,020 lux. Lower light intensity (140 lux) was associated with significantly more severe leaf infection. The development of gray mold along leaves toward the stem was slower at 26°C than at 18 to 20°C and was fastest at relative humidity (RH) levels close to saturation (>99%). B. cinerea infection developed in all stem wounds exposed to 65 to 99% RH and at temperatures of 12 to 29°C. Infection severity in stem wounds (measured as lesion length) on whole plants was significantly less at 26°C than at 18 or 22°C, and was significantly higher at 99% RH compared with 70 to 85 and 85 to 95% RH. Severity of gray mold was the greatest at 15 to 22°C and 85 to 99% RH. Under commercial greenhouse conditions, supplemental calcium (Ca(NO3)2) applied in fertigation or as a spray led to moderate yet significant reduction in disease severity. In addition, polyethylene soil cover and the use of buried drip irrigation instead of surface drip irrigation suppressed gray mold significantly on cut stems following harvest. Covering the soil with polyethylene also suppressed gray mold significantly as compared with the common practice of growing lisianthus in bare soil. [ABSTRACT FROM AUTHOR]