Abstract:

Sequence-specific PCR primers, I-2/5F and I-2/5R were designed according to the sequence from 3 132 bp to 3 765 bp in I-2 gene. With them a 633 bp fragment was amplified from 03F-7 with a genotype of I-2 / I-2, 693 bp fragment from Moneymaker with a genotype of i-2/ i-2, and both fragments from Tebao with heterozygous genotype I-2 / i -2. These two specific fragments were cloned and sequenced. The results from multiple sequence alignment showed that the 633bp fragment from 03F-7 was identical with the sequence from 3 132 bp to 3 765 bp in I-2 gene. Compared with the sequence of I-2 gene, there were a large number of mutations and a 60 bp fragment inserted in susceptible alleles. The PCR primer com-bination, I-2/5F and I-2/5R can be used to distinguish homozygous resistant, heterozygous and homozygous susceptible materials, and it is a functional co-dominant marker in I-2 gene selection. Moreover, this marker was employed on 16 major tomato varieties for I-2 locus genotyping, in which half of the varieties contain I-2 gene, and only one variety is homozy-gous resistant. In addition, simultaneous detection system for I-2 and Tm-22 was established by a single PCR and a Hind III digestion. It provides a powerful tool for multiple genes selection in tomato breeding program.