Development of A, B and R Lines by Gamma Irradiation for Hybrid Rice

Abstract

The development of hybrid rice holds great potential for increasing yields, but there are limitations on how hybrid rice seed can be produced. Exploiting rice male sterility genes is one way to facilitate hybrid seed production, but high yield and vigor in a hybrid depend on heterosis resulting from the genetic diversity of the male and female parents. The objective of this research was to create greater genetic diversity in male sterile, or A lines, maintainer lines, or B lines, and restorer lines, or R lines, for hybrid seed production by inducing mutations using gamma radiation. New A and R lines were created by exposing CP304 hybrid rice to acute gamma irradiation at doses of 0, 100, 200 and 300 Gy. New B lines were developed by taking the F1 generation of crosses between three B lines (IR68886B, IR68888B and IR68899B) and an R line (SPR90119R) and exposing the plants at the booting stage to chronic gamma irradiation at a dose of 416 Gy at the Nuclear Technology Research Center, Kasetsart University. Then they were bred using conventional breeding. Ten A lines and three R lines (RM3) were selected from the irradiated CP304 rice. Ten B lines were selected from the M3 generation of B × R line crosses. Ten counterpart A and B lines were developed by backcrossing to obtain the A(BC1) and BM3 generations. F1 hybrid rice was formed by crossing A(BC1) × RM4 using the line × tester method for 30 crosses. Yield trials revealed that the hybrids gave yields of between 0.89 and 4.73 t.ha-1 with a mean of 2.64 t.ha-1. The highest yielding hybrid was A(BC1)-1 × RM4-1 with a yield of 4.73 t.ha-1. The restorer line RM4-1 had the highest general combining ability. Compared to a standard hybrid rice variety (PTT06001H) with a mean yield of 7.27 t.ha-1, the yield of the hybrids produced in this research was still low because the three R lines were heterozygous (Rr) for the fertility restoration gene and the 30 hybrids segregated into male sterile and fertile plants at a ratio of 1:1. If the R lines can be further developed to be homozygous dominant (RR) then higher yielding hybrids could be achieved.