Morphological traits associated with vegetative growth of rice (Oryzasativa L.) during the recovery phase after early-season drought

• Genotypic differences existed in rice shoot development during the recovery phase after drought stress.
• Upon rewatering, New Plant Type lines prioritized the growth of existing tillers and IR64 prioritized the production of new tillers.
• IR64 rapidly consumed the stem reserves upon rewatering for tiller emergence.
• The difference was linked to the amount of assimilate required to produce new tillers rather than phyllochron.

Rapid leaf growth during the recovery period after a dry spell is essential for the adaptation of rice (Oryza sativa L.) to drought–prone environments. However, how rice plants resume growth when the drought stress ends is not well understood. The objective of this study was to determine the traits and mechanisms associated with the above-ground morphological response to rewatering after early-season drought, by comparing three rice lines with contrastive plant architectures. In the field, we measured the above-ground architecture, carbohydrate partitioning, and consumption of non-structural carbohydrates by IR64 (indica rice), a New Plant Type line (tropical japonica rice) and an IR64 introgression line (IL) with large leaves and reduced tillering under fully irrigated and drought + rewatered conditions. In an ancillary pot experiment, we monitored changes in tiller number and leaf growth under fully irrigated, droughted and drought + rewatered conditions. There were genotypic differences in recovery growth patterns upon rewatering after drought: the New Plant Type lines prioritized individual tiller growth, while IR64 and the IR64 IL prioritized the production of new tillers and concomitantly consumed much carbohydrate. The increase in tiller number during the recovery period was lower in the IR64 IL than in IR64 owing to the longer phyllochron and larger amount of assimilate required to produce new tillers in the IL. Rice development during the recovery period depends on the plant type (constitutive tiller number to size ratio) and tillering response to soil moisture regime, which would be mediated mainly by phyllochron and tiller production per assimilate. Rapid increase in tiller number upon rewatering in IR64 was associated with the low amount of assimilate required to produce new tillers rather than with the short phyllochron.