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Cultivar screening for tolerance to Sclerotinia sclerotiorum using oxalate oxidase gene activity and detached leaf assays

Liezl van der Hoven: University of Pretoria

<div>In South Africa, there is limited information on the susceptibility and tolerance of soybean cultivars currently being planted to the fungal pathogen <em>Sclerotinia sclerotiorum</em>. Detached leaf assays and histological assays were conducted using twenty-nine soybean cultivars commonly planted in South African to screen for tolerance to <em>S. sclerotiorum</em>. No oxalate oxidase gene activity was shown by histological assays, possibly indicating low or no gene expression in cultivars tested. Cultivars differed significantly (P<0.001) regarding percentage diseased leaf area during detached leaf assays, however, temperature and relative humidity means were not significantly different from each other. Cultivar LS 6444 R was found to be most susceptible to <em>S. sclerotiorum </em>at both high and low relative humidity, and cultivars DM 6.8i RR and PAN 1583 R showed higher tolerance under high and low relative humidity, respectively. Cultivars NS 6448 R and LS 6444 R showed more susceptibility at 20°C and 25°C, respectively, while PAN 1614 R and LS 6466 R were the most tolerant cultivars at 20°C and 25°C, respectively. Short to medium growing cultivars showed higher susceptibility to <em>S. sclerotiorum</em>, reaffirming the importance of planting dates in South Africa, to ensure that shorter growing cultivars escape pathogen infection in the field.</div>