Scientists resolve a sterility mystery in tur

Researchers from International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), in Patancheru in Hyderabad, and their collaborators have unravelled a molecular mechanism involved in controlling male fertility in pigeonpea (tur) crop, making it possible to develop better hybrid crops at reduced cost and efforts in future.

Tur is a major pulses crop and is particularly grown in semi-arid areas by smallholder farmers. India accounts for nearly 80 per cent of pigeonpea production in the world. Despite varietal development programmes, the productivity of conventional pigeonpea varieties remained at 700 to 900 kg per hectare. Some commendable efforts by ICRISAT researchers and their partners in the past led to development of hybrids which can yield 30 to 40 per cent more, but this seed production system using current hybrid technology ― called three-line hybrid technology by scientists ― is cumbersome and costly.

In some crops like rice, three-line hybrid technology was converted to two-line hybrid technology by using a particular variety that can become fertile and sterile in different environmental conditions. In this study of the plant at the cellular and protein expression levels, the researchers, including scientists from the University of Vienna in Austria, found that the plants transition from male sterile to male fertile when the temperature of the growing environment is reduced to 24 degrees Celsius. Plant lines that exhibit such reversal of sterility to fertility and vice versa are key to developing hybrids using two-line hybrid technology and are used widely by plant breeders all over the world.

“In our study, we could dissect that this transition is happening just because temperature changes (and not any other environmental conditions), and we determined that that line remains fertile under 24 degrees Celsius and becomes sterile at temperatures higher than 24 degree Celsius,” said Rajeev K Varshney, Director - Centre of Excellence in Genomics and Systems Biology at ICRISAT, who led the study together with another ICRISAT colleague Rachit K Saxena and Wolfram WeckWerth of the University of Vienna. The study appeared in the journal Plant Genome recently.

More importantly, the study found that when auxins ― a class of hormones that plants produce for growth ― applied externally, the plant’s sterility could be reversed up to certain ambient temperatures.

This understanding can help scientists and breeders produce better hybrid pigeonpea varieties using the two-line hybrid technology more easily and at cheaper rates. It may help reduce the cost of seed production by 30 to 50 per cent.

The two-line hybrid technology is more popular among plant breeders. For instance, such a system is popular in rice, where the two-line based hybrid rice occupies about 30 per cent of the total hybrid rice growing areas with up to 5-10 per cent higher yield than the three-line hybrids.

“Technically, the production of hybrid seeds and parental line maintenance would be much easier in the two-line system. However, it is important to mention that specific locations should be identified with the required conditions to implement the two-line hybrid technology (in pigeonpea),” said Varshney.