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.
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