Amarjit SinghLovepreet Singh2023-06-302023-06-302022Lovepreet Singh (2022). Population structure and mating type distribution of Ascochyta rabiei from Northern India (Unpublished M.Sc. thesis). Punjab Agricultural University, Ludhiana, Punjab, India.https://krishikosh.egranth.ac.in/handle/1/5810197876A set of twenty-four isolates of Ascochyta rabiei causing Ascochyta blight (AB) of chickpea were collected from different chickpea growing areas of Northern India. The AB isolates were assessed for their virulence pattern on a set of varieties with varying levels of resistance viz; PBG 5, PBG 7, PBG 8 and L 555. Disease severity was observed as the lowest in case of AB 19 i.e. 2.83, indicating that it was the least virulent isolate on all four varieties. Likewise; the most virulent isolate was observed as AB 1 which showed the highest disease severity i.e. 7.9 on 1-9 rating scale. On the basis of virulence pattern, all the isolates were clustered into two main groups – Group A (14 isolates) and Group B (10 isolates). The mean disease severity of group A ranged from 4.75 to 7.83 whereas in case of group B, the disease severity ranged from 2.83 to 5.17. Genotyping of all 24 AB isolates with 27 SSR loci produced 119 alleles ranging from 2 to 8 in number and 138 to 490 bp in size with an average of 5.42 alleles per marker. The observed heterozygosity was zero in all the populations. This may be due to absence of sexual spores in India and presence of only haploid pycnidiospores of this fungus. Further, the percent variation between the populations was very small i.e. 0.56%. However, the genetic variation within the population was very high i.e. 99.93%. The unweighted neighbour-joining dendrogram grouped the 24 isolates of the three populations into three major clusters. Cluster I included isolates 1 and 6, cluster II consisted of 11 isolates 20, 4, 11, 24, 9, 14, 8, 21, 13, 15 and 18. Cluster III consisted of 11 isolates 2, 5, 12, 23, 3, 19, 7, 16, 17, 10 and 22. Principal coordinated analysis (PCoA) showed that overall, the AB isolates were grouped into four major groups. Clumpak (barplot) clustering of individuals into populations based on multi-locus genotyping grouped the isolates into 3 clusters with an admixture indicating no clear-cut geographical origin-based sub structuring of the population. The MAT1-2 primer amplified in all the isolates giving an amplicon of ~ 800bp whereas MAT1-1 did not amplify in any of the isolates. It indicated that only one mating type ie; MAT1-2 was present in all the AB isolates. For confirmatory study the 800 bp amplicon produced by MAT1-2 primer was sequenced and subjected to BLAST analysis which showed 81.05 to 98.29% homology with Didymella rabiei strain ATCC 76501MAT 1-2-1 (MAT 1-2-1) gene.EnglishThesis