RFLP mapping of a brown planthopper (Nilaparvata lugens Stal) resistance gene bph2 of indica rice introgressed into a japonica breeding line 'Norin-PL4'

A rice gene bph2 for resistance against brown planthopper (BPH), Nilaparvat a lugens St (a) over circle l, was reported to be recessive and either alle lic or closely linked to a dominant BPH resistance gene, Bph1. bph2 was int rogressed from an indica resistance donor variety, 'IR1154-243', into a jap onica breeding line, 'Norin-PL4'. A segregation analysis of BPH resistance in F-2 and F-3 progenies from a cross of a japonica susceptible variety, 'T sukushibare', and 'Norin-PL4', however, showed that the resistance gene in 'Norin-PL4' behaved as a dominant gene. Genotyping of 'Norin-PL4' using 99 RFLP markers covering all 12 rice chromosomes showed that 'Norin-PL4' posse ssed a large segment of chromosome 12 introgressed from 'IR1154-243'. Six R FLP markers on the introgressed segment was cosegregated with BPH resistanc e and bph2 was mapped at 3.5 cM from the closest RFLP marker, G2140. The po sition of bph2 on the standard 'Nipponbare'/'Kasalath' map was at a conside rable distance (about 30 cM) from that of Bph1 previously mapped using a di fferent population. Despite this, no susceptible recombinants were obtained in a large number of F3 progeny from crosses between two Bph1 carrier line s and 'Norin-PL4'. Problems of dominance/recessiveness and no recombination s between the two loci were discussed.