Verticillium wilt caused by race 2 of Verticillium dahliae is common in proportions) was about 5.7 ms per gram of, soil. In five other fields, California on tomato cultivars with the Ve gene for resistance to race 1. however, in which the numbers of race 2 ms were determined, a linear About 47% of 124 isolates of V. dahliae taken directly from tomato field correlation was observed between numbers of race 2 ms (0.0 to 2.0 ms/g of 'soils were race 2; the remaining isolates were either race 1 (43%) or soil) and DI (0 to 100%) when data were plotted arithmetically after nonpathogenic on tomato (about 10%). In contrast, isolates from diseased conversion of DI %to loge (1/ 1-DI) (slope = 2.Oand r =0.877). The line for tomato plants (race I resistant cultivars) from the same fields were the same data plotted on a logio-loge-logio scale had a slope of 1.0(or 1.57 predominantly race 2 (about 86% of 153 tested). Race I was more virulent if assumed to be nonlinear and transformed to logio before regression than race 2 on cultivars lacking the Ve gene for resistance (susceptible). analysis) instead of 0.66, as predicted by Baker et al (10) for abstract Average virulence of race 2 isolates was lower on cultivars with the Ve gene mathematical Model II. Thus, the models and equivalent interpretations than on susceptible cultivars. Incidence of Verticillium wilt (DI) on race I for slopes of lines in arithmetic, logio-logio and log0o-log,-0ogio plots appear resistant cultivars was essentially 100% in 46 fields where soil inoculum to be of questionable validity. density (ID) of total microsclerotia (ms) (race 1 and 2 in undetermined
In a survey during 2000–2002 to determine the identity and prevalence of viruses affecting cucurbit crops in Cyprus, 2993 samples of cucumber, zucchini, melon and watermelon were collected from the five major cucurbit‐growing areas in Cyprus. Zucchini yellow mosaic virus (ZYMV), Papaya ringspot virus type W (PRSV‐W), Watermelon mosaic virus (WMV), Cucurbit aphid‐borne yellows virus (CABYV), Cucumber mosaic virus (CMV) and Squash mosaic virus (SqMV) were detected by enzyme‐linked immunosorbent assay (ELISA), and Cucurbit yellow stunting disorder virus (CYSDV), Beet pseudo‐yellows virus (BPYV) and Cucumber vein yellowing virus (CVYV) by reverse transcription polymerase chain reaction (RT–PCR). ZYMV was the most prevalent virus of cucurbits in Cyprus with an overall incidence of 45%. PRSV‐W, CABYV and WMV were detected in 20.8%, 20.8% and 7.8% of the samples tested, respectively. CYSDV was detected in most greenhouse cucumber samples with yellowing symptoms (88.1%), whereas BPYV and CVYV were found in only 2.4% and 9.5%, respectively, of samples. CMV and SqMV were not detected in any cucurbitaceous crop during this survey.
Outdoor and greenhouse tomato plantings in the main production centres of Cyprus were surveyed for virus diseases during 1978–1982. A disease characterized by prominent leaf yellowing and curling was the most prevalent and damaging. The causal agent was identified as tomato yellow leaf curl virus (TYLCV) because it infected Datura stramonium but not the tobacco cultivars Havana 423 or Virginia, was graft‐transmissible but not mechanically or seed‐transmissible, and was transmitted persistently by the tobacco whitefly, Bemisia tabaci. Minimum acquisition and inoculation feeding periods were 20–30 and 10–20 min. respectively; the latent period was 21–24 h. The vector was infective for about 12 days, but there was no transovarial transmission to progeny.
Four other, mechanically transmissible, viruses were also isolated from tomato and identified on the basis of symptomatology, indicator host reactions and serology; tobacco mosaic virus (TMV), potato virus Y (PVY). potato virus X (PVX), and cucumber mosaic virus (CMV). These viruses, especially TMV, were commonly associated with mosaic symptoms and occasionally with other leaf or fruit disorders; coinfection with TYLCV occurred frequently.
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