QUANTITATIVE GENETICS OF RICE - III - THE POTENTIAL OF A PAIR OF NEW PLANT TYPE CROSSES

This paper reports the results obtained from an investigation of the p otential of two crosses that were taken at random from the new plant t ype (NPT) programme initiated recently at the International Rice Resea rch institute, whose objective is to increase the yield potential of t he direct-seeded, irrigated crop in the lowland tropics to 13 - 15 t/h a. The pedigrees in the NPT programme have been initiated by crossing temperate japonica varieties from China, Japan and Korea with tropical javanica land races from southeast Asia and are, thus, of a novel kin d. The parents, F-1 and F-3 families of each of the two crosses were r aised in completely randomised blocks and their individuals scored for twelve quantitative characters, nine of which were those specified in the NPT ideotype. The results showed that every character was heritab le in both crosses, except for harvest index in the first, their herit abilities being mostly moderate to high. An assessment of the potentia l of these crosses indicated that it should be relatively easy to obta in transgressive segregants from both for the six characters where the NPT targets take the form of an interval, such as days to heading, cu lm length, number of panicles per plant and number of spikelets per pa nicle, but more difficult, if not impossible to accomplish this for pe rcentage of filled spikelets and grain yield, whose targets lie well a bove the parental range. A striking feature of the results obtained fr om the second cross was a marked loss of fertility, in terms of percen tage of filled spikelets, in the F-2 and backcross generations which, it is argued, was caused by the disruption of the independently co-ada pted gene complexes of the parents by recombination and segregation at F-1 meiosis. The pattern of genetic correlations between characters d iffered markedly between the crosses, suggesting that the chief cause of these correlations was the linkage disequilibrium of genes linked i n their inheritance. (C) 1998 Elsevier Science B.V.