The genetic architecture of temperature-induced partial fertility restoration in A1 cytoplasm in sorghum (Sorghum bicolor (L.) Moench)

Cytoplasmic male sterility (CMS) is used for commercial production of hybrid seed in sorghum. CMS-based hybrid breeding systems require female parental lines (CMS lines) to remain male sterile to prevent self-pollination and enable cross-pollination to generate hybrid seed. However, genetic and environmental factors can lead to the loss of male sterility in the pollen-accepting female parent, resulting in the production of contaminating non-hybrid seeds through self-fertilization with large economic consequences. It is known that high temperatures around flowering time induce sterility breakdown, or partial fertility, however the genetic control of this phenomenon is poorly understood. To investigate the molecular processes controlling sterility breakdown, a large association mapping population of elite CMS parental lines was used to map the genomic regions controlling partial fertility. In this study, we used genome-wide association studies on a panel of 2049 sorghum lines grown in six field trials at Emerald Queensland representing six different environments. The seed planting was set up in such a way that flowering corresponded with the hottest part of the year. In total 43 significant SNPs were identified, indicating that the trait is controlled by multiple genes, however previously identified major genes for fertility restoration were not the main cause of partial fertility. Diversity and linkage disequilibrium decay patterns in separate elite male and CMS pools also indicated the constraints on genetic diversity within the female parents due to partial fertility, rather than the frequency of the previously identified major fertility restoration genes. The understanding of the control of sterility breakdown provides new avenues for trait introgression in elite female pools.