Unraveling genotype-isolate interaction in sunflower (Helianthus annuus L.)- Sclerotinia pathosystem using GGE biplot method

Sunflower (Helianthus annuus L.) is one of the most important oilseed crops in the world. Basal stem rot, caused by Sclerotinia spp., is an important disease of sunflower causing considerable yield losses worldwide. Effective improvement for disease resistance relies on the understanding of the interaction between pathogen and host. A total of 100 sunflower genotypes from different worldwide agricultural research institutions were evaluated for their responses to three isolates of each of the S. sclerotiorum and S. minor at the seedling stage in the controlled conditions. Remarkable significant host-pathogen isolate interaction indicates the existence of vertical or isolate-specific resistance in the studied sunflower germplasm against Sclerotinia spp. Genotype-by-pathogen biplot analysis was performed to observe the pathogenicity of the two fungi on host genotypes and facilitate the simultaneous visualization of the relationship among the pathogens and genotypes. The first two principal components accounted for 95.86% and 79.77% of the total variation of the genotype-isolate interaction of S. sclerotrium and S. minor, respectively. The GGE biplot related to S. Sclerotiorum isolates depicted that out of the studied genotypes, "H100A/LC1064" was resistant against the A37 isolate of S. Sclerotiorum. Among the examined germplasm, the genotype "1059" was identified as the resistant genotype against the J2 isolate of S. Sclerotiorum. None of the genotypes were resistant to the J1 isolate of S. Sclerotiorum. Regarding the generated biplot for S. minor, "8A*‎/LC1064C" was the most resistant sunflower genotype against the M1 isolate of S. minor. The genotype "H205A/83HR4" was located in vertex near to A1 and G2 isolates and, therefore, was resistant to these isolates of S. minor. The genetic variation detected within the sunflower collections can be utilized for the selection of diverse parents in the resistant breeding programs as well as the development of mapping populations for the QTL analysis of resistance to S. sclerotiorum and S. minor.