Research Articles (Plant Pathology)

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Browsing Research Articles (Plant Pathology) by Subject "Botrytis cinerea"

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    Frequency of dicarboximide resistant strains of botrytis cinerea in South African table grape vineyards and influence of spray schedules on resistant sub-populations
    (South African Society for Enology and Viticulture, 1998) Fourie, P. H.; Holz, G.
    Between 1993 and 1995, 1139 isolates of Botrytis cinerea were collected from table grape vineyards in the Western and Northern Cape provinces and tested for sensitivity to dicarboximides (vinclozolin) and benzimidazoles (carbendazim). Overall the frequency of resistance to vinclozolin and carbendazim averaged 9,4 and 11,9%, respectively. Ninety-seven percent of the vinclozolin-resistant isolates were dual resistant to carbendazim. Fifty-nine percent of the isolates were from the Hexriver region; of these 7,7% were vinclozolin, and 12,6% carbendazim resistant. The Paarl region had the highest resistance incidence (37,7% vinclozolin and 41,5% carbendazim resistant). Only two of the 191 isolates tested from the Orange River region were vinclozolin resistant. ED50 values of ultra-low-level and low-level dicarboximide-resistant isolates ranged from 0,843 to 1,834 and 2,053 to 5,129 μg vinclozolin/ml, respectively. Vinclozolin-resistant strains were not abnormally osmotically sensitive. Monitoring of changes in the frequency of resistance in 10 commercial vineyards under high-, medium- and low-schedule dicarboximide programmes from 1993-1995 showed that the resistance frequency fluctuated from low (average 12,7% ) during the winter to high (average 55,8 % ) during the growing season. Maximum levels of dicarboximide resistance were recorded during bunch closure. Distinct differences were, however, observed in the resistance frequency in individual vineyards. In four high-schedule dicarboximide vineyards resistance frequencies increased early in the season, prior to any dicarboximide applications. This finding suggests dual resistance between broad-spectrum fungicides and dicarboximides.
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    Use of gamma irradiation for control of postharvest botrytis cinerea bunch rot of table grapes in cold storage
    (South African Society for Enology and Viticulture, 1991) De Kock, P. J.; Holz, G.
    The feasibility of employing gamma irradiation for the control of postharvest Botrytis bunch rot of table grapes in cold storage was studied. Table grape cultivars from commercial vineyards in the Paarl and Hex River Valley areas were packed as for export in vented corrugated cartons. The cartons were irradiated at O; 1,5; 2,0 or 3,0 kGy. After irradiation, grapes were kept for 4 weeks at -0,5°C, followed by another week at 10°C. Less decay was observed when table grapes were irradiated soon after packing than after a storage period. Irradiation at 1,5; 2,0 and 3,0 kGy reduced the effect of Botrytis cinerea on Barlinka grapes stored without sulphur dioxide. Irradiation of Waltham Cross and Barlinka grapes at a dose of 2,0 kGy, combined with reduced S02 treatments, resulted in similar control as with the standard practice of enclosing an S02 generator. Browning of Waltham Cross berries and bacterial and yeast growth occurred on the surface of berries irradiated at a dose of 3,0 kGy. Irradiation had no adverse effect on other aspects of quality.