Characterizing Genetic Variability Among the Rice Grown in the US Midosuth.

Developing early-season vigorous root growth and photosynthetic machinery (canopy development) under variable field conditions are the key for higher yields in many crops including rice.  Thirty six rice cultivars, four replications per cultivar, were grown in pots under sunlit conditions until initial flowering. Root and shoot morphological features were assessed for plants grown for 30 days after sowing (DAS). Mid-season plant growth and development were measured few days after panicle initiation, 64 DAS. Above and belowground growth and developmental parameters were assessed at 30 and 64 days after transplanting (DAS). Several root morphological traits were assessed using the winRHIZO root image analysis system at 30 DAS. The data collected include 11 root traits such root weight, root/shoot ratio, cumulative root length, surface area, average root diameter, volume, root length per volume, and number of roots, tips, forks and crossings. Above-ground and plant growth parameters such as plant height, leaf number, leaf area, tillers, time to panicle initiation, and total and plant-component dry weights were measured at 30 and 64 DAS. Rice cultivars varied significantly for many traits measured. Individual and cumulative vigor response indices were developed from all the traits and cultivars were classified accordingly into different groups. Significant and positive correlations were observed with cumulative vigor response index with leaf area (r² = 0.91), tillers (r² = 0.78) and total dry weight (r² = 0.97) measured at 64 DAS. Root traits showed significant and more variability (5 groups) compared shoot traits (4 groups) among the cultivars for the early-season measurements. Four cultivars showed the higher vigor indices and one and two cultivars showed the least and low vigor indices, respectively, among the 36 cultivars tested. Based on the relative vigor scores assigned in this study, rice producers could select hybrids to maximize rice production in an early planting production system.