Dynamic root responses to drought and rewatering in two wheat (Triticum aestivum) genotypes

Background and aims In Mediterranean-type environments, effective capture of intermittent rainfall is important for crop drought tolerance. Two wheat genotypes RAC875 and Kukri differing in drought tolerance vary in several shoot traits and grain yield. Little is known about root traits contributing to drought tolerance. This study examined dynamic root responses to cyclic drought in these two contrasting genotypes. Methods A pot experiment was conducted by exposing plants to moderate drought before heading, and then rewatering. Root responses were determined for coarse and fine root length density (RLD), root DNA concentration (RDC), nodal root properties, and metaxylem and protoxylem features of both primary and nodal roots in proximal and distal regions. Results Moderate drought reduced fine RLD and inhibited new nodal root growth. Rewatering promoted new nodal root growth. Drought-tolerant RAC875 showed higher relative growth of newly emerged nodal roots than drought-intolerant Kukri after rewatering. RAC875 also had smaller diameter and total area of metaxylem vessels in nodal roots than Kukri, but higher number of metaxylem vessels and RDC independent of water regime. Conclusions Multiple root traits identified could confer RAC875 advantage in drought tolerance under Mediterranean-type environments through conservative use of water and reduced risk of embolism, rapid responses to rainfall and root survival.