Varietal Screening of Compatibility Types Revealed in F1 Fertility of Distant Crosses in Rice

Abstract

Reproductive barriers between distant groups of rice are anticipated to be overcome through a systematic use of widely compatible varieties in breeding programs. For this purpose a total of 74 varieties were screened for compatiblity types in terms of F1 fertility by crossing them to one each of indica and japonica testers. The compatibility of a variety to a tester was rated by pollen and spikelet fertility of the F1 hybrid. The pollen fertility of more than 90 percent and the spikelet fertility of 75-80 percent were rated normal. The compatibility tests showed that the pollen fertility is independent of the spikelet fertility. Therefore, each variety was inspected for four fertility scores, namely, the pollen and the spikelet fertility in each cross to an indica and a japonica tester. Out of 24 Indonesian upland varieties, 15 showed normal pollen fertility with both testers, and normal spikelet fertility with a japonica tester, but gave remarkable spikelet sterility with an indica tester. Six showed semi-sterility in all the four scores. Only one variety, Padi Bujang Pendek revealed normal fertility in all the four scores. The remaing two seemed to belong to an exceptional type. A total of 27 Aus varieties showed many types of compatibility including six varieties of indica type and five of japonica. Five varieties revealed sterility in all the four scores. Only two, Aus 373 and Dular seemed to be widely compatibe. The remaining nine were not classified into any difinite categories. In the test of 15 varieties which are identified tolerant of salinity, drought or peat soil, ten of strongly photoperiod-sensitive varieties were classified into typical indica rice. Two photoperiod-nonsensitiwe varieties were clearly identified to be japonica. In additional tests of some varieties which are notable from previous works, Calotoc, CPSLO 17 and Ketan Nangka were confirmed to be widely compatible. The screening results indicate that the Aus group of rice is a complex of various compatibility types, while a majority of Indonesian upland rices seemed to be of a type which is closer to japonicas rather than iledicas. Only a few varieties were identified as the wide-compatibility type, contrary to the expectation based on earlier works. It was discussed that the upland cultivation has permitted the Aus group to preserve the diverse compatibility types, while photoperiod-sensitive lowland varieties are predominantly of iledica type.