Assessment of genomic diversity of wild and cultivated tomato through resistance gene analogue polymorphism and I2 homologues

Abstract

Plant disease resistance gene analogue polymorphism (RGAP) in tomato has been studied on the basis of NBS-LRR (Nucleotide Binding Site-Leucine Rich Repeat) class of genes using degenerated primers. Results revealed variable degree of polymorphism of the Group II compared to the Group I class of R genes. The probable explanation could be further diversification of the Group II class within tomato genotypes compared to the Group I class, which is relatively conserved. Furthermore, investigation of the diversity of the I2 class of genes, responsible for resistance to Fusarium oxysporum f.sp. lycopersici, revealed that genomic PCR mediated identification of functional I2 using the specific primers designed from the conserved domain of LRR region of I2 class of genes, is not possible on the basis of amplified fragment size. On the contrary, PCR amplification of 249 bp fragment from the conserved LRR region of I2 homologue I2C1/C2 gene from all the resistant lines indicated co-segregation of I2C1/C2 to the susceptible background along with the I2 gene during introgression. This may be an indirect PCR-mediated approach for marker-assisted breeding of functional allele of I2.