Modelling possible benefits of root related traits to enhance terminal drought adaptation of chickpea

Chickpea is cultivated at the end of the rain in tropical and sub-tropical regions like in India. Crop growth depends on the soil moisture contained in the soil profile, commonly leading to terminal water deficits. The past three decades of research have focused on improving rooting traits, with a particular focus on the speed of root extension in the soil, making the assumption that this would lead to more water extraction. Here, we used a robust crop simulation model to assess genetic and management modifications that would affect water availability to the crop. Against expectations, increasing the rate of depth of root extension to 30 mm day−1 from a baseline of 17 mm day−1, to reflect the characteristics of an existing root trait quantitative trait locus (QTL) on linkage group 5 of chickpea, brought about a yield penalty in all situations (4–6%), especially in locations where the in-season rainfall was low (up to a 15% yield penalty). By contrast, modifying soil characteristics by increasing the depth of effective water extraction from 1000 mm to 1200 mm led to yield increases in all situations (8–12%) as a result of greater water available at the end of the growing season. Changing the rate of leaf area development rate associated with the root QTL locus on LG5, had no impact on yield except for a yield increase at the two highest yielding locations. The greatest changes in yield were obtained by irrigating the crop with 30 mm at R5 (beginning of seed growth). The average yield gain across all locations was 29% and the high yield benefit was achieved across all yield levels. These results indicated that some benefit would come from growing the crop in soil with a higher depth of effective water extraction, which may require faster root growth in very low rainfall environments, but the greatest yield benefit would result from modest irrigation at R5.