Combining drought QTLs and bacterial blight Xa-genes to control bacterial blight disease under drought stress

Crops under climate change will be simultaneously exposed to multiple stresses of biotic and abiotic nature. To control rice bacterial blight (BB), near-isogenic lines carrying Xa genes were previously developed, while rice near isogenic lines (NILs) with drought yield QTLs (qDTY) were selected for rice yield improvement under drought conditions. In this study, the response of 17 rice lines to simultaneous BB and drought stresses were evaluated in screenhouse trials and field trials to evaluate their response to exposure to BB and drought simultaneously. Under drought stress, qDTY NILs with their shorter growing period were less affected, while IR24 and IRBB4 showed growth reduction and inhibition of flowering under field conditions. NILs with BB resistance (R) Xa gene alone showed resistance to Xanthomonas oryzae pv. oryzae (Xoo) strains carrying the corresponding avirulence gene, except in genotype IRBB4 with the Xa4 R gene that, although resistant, showed a significant increase in disease severity under drought stress after inoculation with Xoo strain PXO61 (avrXa4) compared to irrigated conditions. IR64 introgression lines (IR87705-6-9-B, IR87707-445-B-B-B, IR87707-446-B-B-B) with the combination of the Xa4 R gene and qDTY showed resistance to Xoo strains PXO61 (avrXa4) and PXO145 (avrXa4) under irrigated conditions but were less resistant under drought. Vandana qDTY NILs were susceptible to all Xoo strains under both irrigated and drought stress conditions, but were more resistant under drought. These results highlight the wide genotypic variation among rice lines in response to BB under drought stress and the advantage of trait combinations (Xa+qDTY) to confer drought tolerance and BB resistance under unfavorable future climate conditions. (C) 2016 Elsevier B.V. All rights reserved.