Rooting traits of peanut genotypes with different yield responses to terminal drought

Drought at pod filling can severely reduce yield of peanut. Better root systems can reduce yield loss from drought. However, the relationship of root characters with yield under terminal drought is not well understood. The objective of this study was to investigate the responses of peanut genotypes with different yield responses to terminal drought stress for root dry weight and the percent root length density (% RLD) in deeper soil layers and their relationships with biological and economic yield. A field experiment was conducted at Khon Kaen University's Agronomy Farm in 2010/2011 and 2011/2012. A split plot design with four replications was used in this study. Five peanut genotypes: ICGV 98308, ICGV 98324, ICGV 98348, Tainan 9 and Tifton 8 were assigned as subplots and two soil moisture levels [field capacity (FC) and 1/3 available water (1/3 AW) at R7 growth stage through harvest] were assigned as main plots. Data for root dry weight, % root length density (% RLD), stomatal conductance, water use efficiency (WUE), pod yield, biomass, harvest index (HI), were recorded at harvest. Drought significantly reduced pod yield, biomass and HI. Overall genotypes, yield responses to terminal drought were not correlated with root dry weight and % RLD. However for some genotypes, yield under terminal drought did seem to be related to root dry weight and % RLD. The genotypes with large root system and high stomatal conductance, WUE and biomass and maintained higher pod yield under terminal drought. For example, Tifton 8 had high root dry weight and high stomatal conductance, WUE and biomass, maintained higher pod yield under drought conditions. Peanut genotypes that have high % RLD at deeper layers and high stomatal conductance, WUE and HI might also maintain pod yield under terminal drought. ICGV 98324 and ICGV 98348 increased % RLD at deeper layers and also had high stomatal conductance, WUE and HI and maintained higher pod yield under terminal drought. Percent RLD could be useful as a selection criterion for improving resistance to drought. However, selection of RLD alone can be confounded because some genotypes with high RLD under terminal drought had low pod yield, and selection of RLD as a supplement for pod yield under drought would be more effective.