Water deficit and impaired pegging effects on peanut seed yield: links with water and photosynthetically active radiation use efficiencies

Peanut (Arachis hypogaea L.) production is frequently affected by unpredictable events of water deficit during pod set, which modulate water use, water use efficiency for biomass production (WUEB), and biomass partitioning to seeds. We studied the effects of drought-induced impaired pegging on WUEB and the link between WUEB and photosynthetically active radiation use efficiency (PAR-UE). Field experiments were conducted that combined: two cultivars of contrasting pegging capacity (ASEM > Florman), two water regimes (irrigated and water stress) and different sowing dates. WUEB ranged between 6.1 and 6.7 g kPa/mm for irrigated plots, and between 2.9 and 7.1 g kPa/mm for water-stressed plots. WUE for pod production showed similar trends, but was larger for ASEM than for Florman because of higher biomass allocation to pods and pegging capacity of the former. The relationship between standardised values of WUEB and PAR-UE varied linearly for the post-R6 period, but fitted models differed between water regimes. This difference was attributed to the relative importance of stomata control on gas exchange (direct effects of water deficit) respect to feedback effects on photosynthesis caused by reproductive sink size (indirect effects of water deficit). Variation in post-R6 PAR-UE could be linked exclusively to the latter, but variation registered in WUEB acknowledged both controls.