Genetic analysis of the low critical sterility temperature point in photoperiod-thermo sensitive genic male sterile rice.

It has been a long haul but photoperiod- and thermo-sensitive genic male sterile (PTGMS) rice has not been freely used in hybrid rice production because there are two perplexing problems corresponding to the critical sterility temperature point (CSTP): the uncertainty of the CSTP segregating pattern and the instability of CSTP for every originally useful line. N5088S, the most widely commercialized japonica-type PTGMS line in China, also saw that its CSTP variants have been isolated but with all other agronomic characteristics unchanged. In this report we analyzed the genetic basis of CSTP, by employing the iterated expectation and conditional maximization (IECM) algorithm on four tiller-splitting-formed sets of seven generations from N5088S and its CSTP-variant H5088S, each set treated with one temperature regime. The main results indicated that there are two dominant major genes and polygene, as well as their respective epistasis conditioning the CSTP in the 23.5 degrees C regime. Based on the results obtained, the strategy for breeding of PTGMS lines with stable low CSTP was outlined.

Characterization of interspecific hybrids and backcross progenies from a cross between Oryza minuta and Oryza sativa.

Oryza minuta, a tetraploid wild relative of cultivated rice, is an important source for the genetic improvement. Interspecific hybrids were obtained from the cross of O. sativa L. (IR24) and O. minuta (Acc. No. 101133) with 5.58% crossability, which ranged from 0.11% to 1.62% in the backcross generations. The chromosome numbers of the backcross progenies were 24 to 48. Seven yield-related traits of the parents, hybrid F(1), and backcross progenies were evaluated. Simple sequence repeat markers analysis showed that the polymorphism ratio of SSR bands between IR24 and Acc. No. 101133 was 93.2%. The average donor segment number, length, donor genome size, and percentage of donor genome of 92 BC(3)F(1) plants (2n=24) were 24.1, 17.8 cM, 438.4 cM and 26.2%, respectively. They were complex variation and uneven among the chromosomes. These introgression lines could be used to identify the favorable genes of O. minuta and provide a new platform for the genetic improvement of cultivated rice.