Variation of yield and physiological characteristics of Lathyrus sativus L. populations under terminal drought

Grass pea is one of the oldest native crops grown in vast geographical regions of Iran, however ‎little is known about its tolerance to water shortage during post flowering period. We conducted ‎field experiments in 2018 and 2019 to study the effects of terminal drought on growth, yield, and ‎some physiological characteristics of grass pea (Lathyrus sativus L.) ecotypes. Nine local grass pea ‎ecotypes (Baft_1, Baft_2, Bardsir, Dehbakri, Kuhbanan, Rabor, Sirjan, Shiraz, and Torbat ‎Heydarieh), collected from different climatic regions in the east, southeast, and south of Iran, were ‎exposed to either normal irrigation or terminal drought (water withholding after flowering). Normal ‎irrigation was applied after 60 mm water evaporation from class A evaporation pan for the whole ‎growing season. Terminal drought decreased seed and biological yields, relative to normal ‎irrigation, with Baft_2 and Rabor the superior ecotypes in both treatments. Among yield traits, pod number per plant had very high correlation with seed and biological yields in either irrigation regime and was the highest in high yielding ecotypes. Leaf surface area, relative water content (RWC) and starch content decreased while soluble sugars and proline content increased by terminal drought. The highest yielding ecotypes, Baft_2 and Rabor had not the highest leaf area and RWC though they had the highest starch content under normal and sugars content under terminal drought. Also they had the greatest water use efficiency in both years and watering regimes. Proline content, RWC and sugar contents did not significantly correlate with seed or biological yield under terminal drought. Our results suggest that drought tolerance in ‎grass pea is closely associated with better utilization of water and plant photosynthetic capacity, as reflected in high starch ‎accumulation and conversion to sugars, perhaps as an osmotic adjustment factor. Also, high yielding ecotypes allocated higher dry matter to reproductive tissues.