Assessing diversity and grouping of rice genotypes based on some root architectural traits

Plant roots are important in minimizing the yield gap and underpinning the second green revolution that must meet human food demand. This hidden half of the plant is a conduit for resource uptake from the soil. It is logically a valuable target in breeding to improve crop productivity in nutrient-deficient soils. The continuous breeding of shoots in the past decades has ignored the root's phenotypic, morphological and anatomical diversity despite the available genetic resources. However, the changes in root characteristics according to their genetic background in rice have not been fully characterized. Few cultivars or stands with unknown genetic backgrounds were used in the studies. This research aimed to investigate the phenotypic diversity of some root traits in rice genotypes, evaluating correlations between root traits and grouping varieties based on root morphological traits. This research was conducted to evaluate the root characteristics and screen varieties with superior root traits at Rice Research Institute of Iran (Rasht) in 2022. In this research, 40 genotypes, including local varieties and modified Iranian and exotic genotypes, were grown in pots in a completely randomized design (CRD) with three replications. At the end of the rice growth period, root traits including root length, root volume, root area, and root-to-shoot ratio, were measured. Statistical analysis was performed with SAS software (9.4 version). The analysis of variance showed that the genotype effect was significant at the 1% probability level in root length, root volume, root area, and root-to-shoot ratio. The mean comparison results showed that the Kapa genotype had the largest root length (53.7 cm), the Avanqard genotype had the largest volume (92 cm3) and root area (245.9 cm2), and the Dijla genotype had the highest root-to-shoot ratio (0.49). Cluster analysis placed the studied genotypes into three separate groups. The first group had values ​​almost equal to the total average of studied root traits. The second group had root volume and area lower than the total average and the third group had root volume and area greater than the total average. Correlation evaluation between investigated root traits showed that root length positively and significantly correlated with root area. A positive and significant correlation was observed between root volume, root area, and root-to-shoot ratio. The root area also positively and significantly correlated with other studied traits. The results of this study indicated the existence of diversity in root architectural traits in the evaluated genotypes. Based on cluster analysis, the genotypes of the second group had root volume and area less than the total average, and the genotypes of the third group had root area and volume greater than the total average. Therefore, genotypes of the third group of cluster analysis, such as the Avanqard, due to their larger root volume and area, are recommended for use as parents in breeding programs.