Characterization of cotton root rot pathogens - Rhizoctonia solani and R. bataticola using RAPD and morphological markers.

摘要

An experiment was conducted to differentiate isolates of cotton root rot pathogens (23 isolates for Rhizoctonia solani and 25 isolates for Rhizoctonia bataticola [Macrophomina phaseolina]) collected from north India (Haryana, Punjab and Rajasthan) using RAPD markers and to study the relationship between molecular variability and pathogenicity. R. solani isolates HR-7, RJ-1, H-3-10, RJ-3-6 and Rs-CMB caused 100% mortality of the inoculated cotton (Gossypium arboreum) seedlings. R. bataticola isolate RJ-28 caused significantly high mortality. Studies of morphological characters of R. solani isolates revealed that the variation in colour ranged from creamish to brown mycelium. However, cultural characteristics varied for R. bataticola isolates. Variation in the whitish mycelial growth on the surface of black mycelial mats and pigmentation was noted in different cultures and broadly classified into 4 groups. For R. solani, isolates 2, 3, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15 and 16 (group I) were clustered in one large group having genetic similarity (0.86-1.0). The isolates 19, 20, 22 and 23 (group II) were closely related with genetic similarity 0.63-1.0 but showed diversity from isolates 17, 18 and 21 (group III), and isolates 1, 4 and 11 (group IV), which showed similarity coefficient ranging from 0.82 to 1.0 and 0.56 to 1.0, respectively. R. bataticola isolates were classified into 2 boad groups, where group I consisted of isolate 16 having 0.59 genetic similarity and was most pathogenic. Group II was further clustered into 5 subgroups. The RAPD method revealed polymorphism within isolates of R. solani and R. bataticola thereby indicating usefulness of DNA fingerprinting for race/biotype characterization. However, there was no strict correlation between grouped isolates based on pathogenicity, morphological features and RAPD fingerprinting. Nevertheless, reproducible genetic variability is delineated that distinguished and differentiated isolates of both Rhizoctonia species. Dendrogram obtained from all 48 isolates showed 2 distinct groups (groups I and II) of isolates. Group I accommodated most of the isolates of R. solani and R. bataticola. Group II was further subdivided into 2 subgroups and consisted of isolates 1, 4, 11, 19, 20, 22 and 23 of R. solani, and isolates 12, 14, 16 and 22 of R. bataticola.