Towards a Promising Two-Line Hybrid System with the Discovery of a Temperature Sensitive Male Sterile Line in Pigeonpea (Cajanus cajan)

In pigeonpea, cytoplasmic-nuclear male sterility (CMS) based hybrid technology has been successful in achieving higher yield. However, its cumbersome nature, labor-intensive and expensive seed production has led to explore the possibility of a two-line hybrid breeding system. This two-line hybrid system depends on the male sterile line which precisely responds to environmental factor(s) for their sterility and fertility, so as to participate in the hybrid program as well as for its own seed production. Towards this goal, the environment-sensitive male sterile lines derived from C. sericeus were used for the present study. Fertility alteration in response to more than 20 different combinations of temperature, photoperiod, humidity and light intensity (under controlled growth conditions) were studied. As a result, day temperature was identified as the key environment factor for fertility alteration. On the other hand, cytological studies revealed that the pollens lose their viability only after the tetrad stage in sterile anthers. In order to identify putative candidate genes involved in this phenomenon, RNA sequencing from the anthers of this critical stage was carried out. A total of 18.5 million paired-end reads were generated using Illumina Miseq platform and were analyzed to identify 126 induced and 98 repressed differentially expressed transcripts in sterile samples. Interestingly, the biological processes such as oxidation-reduction are significantly induced and cell wall modifications are significantly repressed. This study has led to the identification of a temperature sensitive male sterile (TSMS) line and candidate genes which are the pre-requisites for a two-line hybrid system.