RAPD markers for resistance to Alternaria solani (early blight) in cultivated tomato (Lycopersicon esculentum L.)

An attempt was made to understand the genetics of resistance against Alternaria solani in tomato (Lycopersicon esculentum L. cv. 'Megha'), and to develop molecular markers as an effective strategy to assist in the transfer of resistance. The F-2 segregation pattern of a resistant x susceptible ('Megha' x 'Pusa Gaurav') cross revealed the trait to be governed by two recessive genes. Efforts were made to develop RAPD markers to these two recessive resistance genes. Out of 14 random primers that were polymorphic between the parents, two primers (OPG19 and OPE11) produced unique amplicons 1,350 bp and 1,300 bp in length, respectively, that co-segregated in repulsion phase (i.e., were linked to the susceptible disease reaction in F-2 bulks). Single marker analysis also revealed significant differences between the marker genotypes of 75 F-2 individuals, indicating a linkage between the disease reaction and the individual markers OPG19(1350) and OPE11(1300). A best-fit ratio of 9:3:3:1 between the two markers, OPG19(1350) and OPE11(1300), revealed that they were not linked to each other, suggesting that the markers were linked to two different loci governing the resistance trait. This is the first report of RAPD markers for resistance to Alternaria solani in tomato.