Abstract

An effective rice callus screening method for breeding disease-resistant regenerated plants of sheath blight caused by Rhizoctonia solani Kühn is yet to be developed. In this study, callus-resistant rice was screened using pathogenic crude toxins of highly virulent isolates, R. solani (Anastomosis Group 1-IA) collected from Sichuan Province, China. Highly susceptible rice cultivars, Lemont and moderate resistant rice cultivar, Kasalath were used for callus screening. The detached leaf and micro-chamber methods were used to evaluate the resistance of the regenerated plants (R₀) and their offspring (R₁). The disease resistance levels of R₀ and R₁ obviously improved when compared with the control (P>0.05). Rice seedlings were inoculated with 0.25 g of R. solani mycelium (fresh weight) at the base of the plant and then covered with transparent plastic bottles to maintain high humidity after inoculation. The resistance of R₁ was enhanced than their progenitors, the disease index of R₁ of Kasalath was 2.27 which was higher than that of IR64, 9311, TeQing and Gan72, while the disease index of R₁ of Lemont was 3.14 which was higher than that of 9311, TeQing and Gan72. According to the nine-grade disease classification, the R₁ of Lemont was moderately resistant, while the R₁ of Kasalath was resistant.

Key words: Rhizoctonia solani Kühn, toxin, micro-chamber method, disease index, stem lesion heights, highly resistant cultivars.