Genetic analysis of resistance to green rice leafhopper (Nephotettix cincticeps UHLER) in rice parental line, norin-PL6, using RFLP markers

Abstract

We first characterized the graphical genotype of a japonica rice parental line, Norin-PL6 (Ou-PL1), which was bred to introduce the resistance genes to the green rice leafhopper (Nephotettix cincticeps UHLER: GRL) from an indica rice variety, Lepe-dumai, in order to identify the chromosome loci of resistance genes, using restriction fragment length polymorphism (RFLP) markers. It was observed that two chromosome segments introduced from Lepe-dumai were located on chromosomes 3 and 11, based on the Lepe-dumai RFLP patterns on chromosomes 3 and 11, respectively indicated by neighborly five and two RFLP markers. Moreover, two quantitative trait loci (QTL) with major genic effects and interactive function, were detected in these regions on chromosomes 3 and 11, based on QTL analysis between the degree of resistance to GRL and the RFLP data in seventy-six B1 F1 plants derived from the combination between the F1 hybrid of Toyonishiki/Norin-PL6 and Toyonishiki a japonica susceptible variety used as a recurrent parent. Although, it had been already reported that the resistance of Norin-PL6 was controlled by two or three dominant complementary genes, one of them being Grh2, the gene symbol and chromosome location for the other resistance gene(s) had not been determined. It is inferred that the two QTL on chromosomes 3 and 11 corresponded to the dominant complementary genes for resistance. Moreover, no other resistance genes to GRL have been reported on chromosomes 3 and 11. Based on these results, we designates Grh4(t) as one of the complementary resistance genes in Norin-PL6, and confided it as a new gene. We could not determine whether Grh2 and/or Grh4(t) were located on chromosome 3 or 11, but we identified the RFLP markers which were linked to these resistance genes. These markers will enable would be useful to develop improved varieties or isogenic lines for resistance to GRL by the application of the marker- assisted breeding method. We will attempt to develop two kinds of isogenic lines which harbour independently each complementary gene for resistance using the RFLP markers, in order to elucidate the genetic mechanism of resistance to GRL and determine the location on chromosomes in Norin- PL6 in detail.