Anastomosis and cross-infection potential of Rhizoctonia solani: a comparative study of rice and potato isolates

Potato is planted after rice in different parts of India, especially in Haryana, as a part of the rice-potato sequential cropping system, and both crops are infected by Rhizoctonia solani Kuhn. Potato tubers exhibiting black scurf and rice plants affected by sheath blight were collected from various regions of India, and isolates of R. solani were obtained. Cross-infection potential of R. solani was assessed by inoculating rice isolates onto four potato cultivars and potato isolates onto four rice varieties. None of the potato isolates infected any of the rice cultivars under laboratory or screen house conditions. In contrast, rice isolates showed weak pathogenic reactions on three potato cultivars, while the cultivar Kufri Khyati remained unaffected. The complete resistance of Kufri Khyati against all rice isolates highlights its potential for use in a resistance breeding programme. Cross-infection studies showed directional asymmetry in the cross-infectivity of R. solani isolates between rice and potato. Anastomosis behaviour of rice and potato isolates (within and between) was tested based on hyphal interactions. Our study indicates that strong compatibility exists only within host populations (79 in rice and 29 in potato) and fewer incompatible reactions (8 in rice and 5 in potato). However, among 198 cross-host pairings of rice and potato, no interactions resulted in perfect cytoplasmic fusion, indicating clear incompatibility between rice and potato isolates, likely due to differences in anastomosis groups (AGs). Among host groups, isolates R8 from rice and P8 from potato recorded the highest number of compatible interactions, suggesting greater potential for anastomosis and genetic exchange. The present study highlights the possibility of anastomosis and cross-infectivity among R. solani isolates of rice and potato in the rice-potato sequential cropping system in Northern India.