Cytogenetic analysis of cytoplasmic male sterility in wheat line KTP116A and molecular mapping of two thermo-sensitive restoration genes

The cytoplasmic male sterile (CMS) wheat (Triticum aestivum L.) line KTP116A developed at Northwest A&F University, Yangling, China, was sterile at temperatures below 18 °C and fertile at temperatures above 20 °C during Zadok’s growth stages 45–52. The possibility of a two-line system has a promising future for hybrid wheat production. The present study describes morphological differences in pollen abortion behavior at different temperatures, and the genetics of the thermo-sensitive restorer gene(s) in line KTP116A. Cytological observations showed that abnormalities in development of male sterile anthers first appeared at the bi-nucleate stage. Only a few pollen grains go through the second mitosis to produce two sperm cells; most of those became abnormal pollen grains and shell structures without protoplast, confirming that the conversion from sterility to fertility in the CMS line was accompanied by changes in morphology and cytology. A BC₁ population of 198 plants from a cross of male-sterile KTP116A and male fertile F₁ TP116B/WM5-5 was developed to study the genetic control of thermo-sensitive sterility. Chi squared tests on data from back-crossed populations revealed that two recessive genes, designated rfv ₁ ^sp and rfv ₂ , were responsible for sterility of line KTP116A. Sixteen of 712 SSR markers were polymorphic between the parents and bulks. Four SSR markers, viz. Xgwm11, Xgwm18, Xgwm413 and Xbarc137, were linked to thermo-sensitive gene rfv ₁ ^sp on chromosome 1BS of T. spelta, and another four markers were linked to rfv ₂ located on chromosome 2A. This thermo-sensitive male sterile line can be used for production of experimental hybrids in order to test levels of heterosis.