Classification of root distribution patterns and their contributions to yield in peanut genotypes under mid-season drought stress

Abstract

Peanut root distribution patterns are not well understood and have not been studied extensively. There is a lack of information on the classification of root distribution patterns for many peanut genotypes and the relationship between rooting traits and yield under mid-season drought, which could be useful for breeding for drought tolerance. In this study the root distribution of 40 peanut genotypes with different drought tolerance levels and different sources of origin was evaluated during the dry seasons of 2007 and 2008 at Khon Kaen University, Thailand. A randomized complete block design with four replications was used in both years. All plots were well-irrigated except when water was withheld from 50 to 83 days after planting (DAP) during the first season and from 50 to 87 DAP during the second season to emulate a mid-season drought. Top dry weight was observed at the most water-stressed date and at harvest, while root data were measured at the most water-stressed date using the auger method. The soil was sampled to a depth of 90cm and was separated into the upper (0–30cm), middle (30–60cm) and deeper (60–90cm) soil layers. For each peanut genotype, the relative contribution to each layer was calculated and defined as root length density percentage (%RLD). Pod yield was observed at final harvest date and pod harvest index (PHI) was calculated as pod dry weight per unit of total biomass. The forty peanut genotypes were categorized as either high or low %RLD depending on the mean of %RLD in each layer for the three soil layers. These peanut genotypes were then categorized into six combinative groups, based on the high vs. low %RLD for each of the three layers. The relationship between %RLD in the lower soil layer and yield was significant and positive for both seasons, indicating that %RLD in the lower layer is an important trait that affects pod yield under mid-season drought conditions. There was a negative relationship to %RLD in the upper layer in one season and no relationship to %RLD in the middle soil layer for both seasons. The results from this study also indicated that PHI was an important trait that is associated with maintaining pod yield under mid-season drought.