Evaluation of greenhouse inoculation techniques used to screen for Sclerotinia stem rot resistance in soybeans

Abstract

Numerous inoculation methods have been used to screen soybean germplasm for resistance to Sclerotinia stem rot, caused by Sclerotinia sclerotiorum. This study was conducted to compare six inoculation methods viz. (i) spray mycelium, (ii) drop mycelium, (iii) cut stem, (iv) cotyledon inoculation, (v) straw inoculation and (vi) petiole. Four soybean cultivars were planted in 1–l pots in the greenhouse and grown to V3 (third trifoliate) growth stage. Overseeded pots were thinned to four plants which were inoculated using the respective methods and covered for nine days with transparent plastic bags. Plants were arranged in a randomized block design with eight replicates. The number of infected plants was counted and leaf lesion development and degree of plant wilting were scored using a 0 to 5 rating scale. The spray mycelium method yielded the highest incidence of wilting although a significant cultivar × inoculation technique (P<0.05) was recorded, particularly where host tissues were damaged prior to inoculation. Results suggest that cultivar responses are affected by the degree and area of tissue damage associated with the respective inoculation methods.