Genetic Analyses of Male Sterility and Wide Compatibility in U.S. Hybrid Rice Breeding Lines

Abstract

Two line hybrid rice breeding is widely used in Asia and involves the use of environmentally-sensitive male sterile lines to achieve high grain yields compared to pure line varieties. Currently, there is limited information concerning the performance and inheritance of two indica male sterile lines 2008S and 2009S under U.S. field conditions. The first objective of the research herein was to characterize genetic male sterility of lines 2009S and 2008S under controlled environment conditions. Results showed that 2009S exhibited a thermosensitive response whereas little or no response was observed with changes in daylength. Furthermore, high pollen fertility was achieved at the proper developmental stage (flag leaf not fully exposed) under low temperature treatment for 10 days. On the other hand, 2008S showed partial fertility when subjected to short daylength and high temperature conditions. Both lines were completely male sterile at high temperature and long daylength under Louisiana field conditions. The second objective was two-fold: to investigate the inheritance of photoperiod, thermosensitive genetic male sterility (PTGMS) under field conditions and to evaluate SNP-based markers for male sterility. A three-year study of 2008S F2 and BC1F2 populations from 2012 to 2014 revealed a two-locus segregation model indicating two recessive genes acting on male sterility. Inheritance of 2009S in a two-year study from 2013 and 2014 displayed single locus segregation using F2 and BC1F2 populations demonstrating that male sterility was controlled by a single recessive gene. SNP markers at LOC_Os07g12130 and LOC_Os12g36030 in the 2008S background showed significant interactions with up to 65% variance explained in one population, while a SNP marker at LOC_Os02g12290 identified 90-100% of male sterile lines segregating in F2 and BC1F2 populations derived from 2009S. The third objective was to conduct QTL mapping for male sterility in populations derived from 2008S using a selective genotyping approach. A total of five major QTLs including those previously identified in LOC_Os07g12130 and LOC_Os12g36030 and eight new minor QTLs were detected using single marker analysis. Four QTL intervals were detected with a LOD score of greater than 3.0 using inclusive composite interval mapping (ICIM). QTLs identified will be useful in future studies to fine-map additional markers associated with male sterility and increase prediction accuracy for marker assisted selection. The fourth objective was to investigate the effect of the S5n wide compatibility gene on grain yield and spikelet fertility in hybrids derived from the SB5 RIL mapping population. Results from this study revealed that