Genetic Variability in Root Traits Among Spring Wheat (Triticum aestivum L.) Genotypes.

Productivity of wheat under dry land conditions is limited by drought stress. Root traits are critical for soil exploration and resource (both nutrients and water) capture and thus are important for crop improvement under drought conditions. The objective of this study was to quantify genetic variability for root traits in Washington State University (WSU) World Wheat Collection, consisting of 296 spring wheat genotypes. Single plants of all genotypes were grown in 1.5 m columns with Turface as rooting medium, under well watered conditions, in a green house. The experimental design was randomized complete block with two replications. Optimum temperature conditions (25/15°C, maximum/minimum) were maintained from planting to final harvest at 61 days after planting. Data on plant height, number of tillers, and rooting depth were recorded. Roots of selected genotypes with maximum, minimum, and intermediate rooting depth were subjected to complete image analysis (WinRHIZO software) for quantifying traits such as total length, surface area, and volume of total root mass and of roots of various classes (diameter, 0 to 0.25 mm, 0.25 to 0.5 mm, 0.5 to 1.0 mm, 1.0 to 2.0 mm, >2.0 mm). Wheat genotypes differed for above and below–ground traits. Range of major root traits was as follows, (a) rooting depth – 45 to 187 cm, (b) total length – 720 to 7112 cm, (c) total surface area – 85 to 1126 cm², and (d) total volume – 0.8 to 15 cm³. There was no correlation between rooting depth and plant height. Overall, genotypes KSG 233, 220, 241 and 267 were ranked high and genotypes KSG 183, 89, 176, and 31 were ranked low for rooting depth and other root traits. These results indicate that considerable genetic variability exists in WSU World Wheat Collection for root traits that can be exploited to improve drought tolerance and/or resource capture in wheat.