The development of a wax petrolatum layer method for screening the ability of rice (Oryza sativa L.) roots to overcome mechanical impedance is utilized in this study to identify drought tolerant lines. The ability of roots to penetrate compacted soils can be beneficial in terms of water uptake for avoiding drought stress. However breeding for root penetration is hindered by the lack of an efficient and reliable screening technique. Our objective in this study was to evaluate the use of a wax-petrolatum layer system as a reference to measure genotypic variation in root penetration ability of 28 rice (Oryza sativa L.) genotypes. The wax- petrolatum layers consisted of 60% wax and 40% petrolatum white, with a penetration resistance strength of 1.4 Mpa at 27 degree Celsius. The wax- petrolatum layers were placed in plastic cups and served as a partial barrier for root penetration. Rice cultivars were sown in a randomized complete block design with two replications and grown in screen house. Drought stress was imposed at 25 days after sowing. Root sampling was done on 40th day after sowing and several root morphological characters viz., root length, shoot length, root volume, basal root thickness, root fresh weight, shoot fresh weight, root dry weight, shoot dry weight, and root shoot dry weight ratio were measured. Based on the drought screening under wax petrolatum screening method, the genotypes viz., Norungan, Kallurandaikar, CB 09 516, CB 06 803, CB 08702, IR 83376-B-B-110-2, IRGC 12931, IRGC66774, Anna 4, IRGC 99696 and IR 72024 were identified as drought tolerant and the genotypes viz., IR 84882-B-120-CRD-4-1, IR 2715-13-IR-84887-B-154, IR 84895-B-127-CRA-5-5-1 and IR 1570-418-149-1 were found to be susceptible based on drought score index. PCV was marginally higher than the GCV for all traits. Heritability was high for all the traits studied i.e. root length, shoot length, root volume, basal root thickness, root fresh weight, root dry weight and shoot fresh weight except for shoot dry weight which has shown moderate heritability. Root length had high and positive correlation with shoot length, root volume and root dry weight. Root volume had significant and positive correlation with root thickness and root dry weight. Root thickness had positive correlation with root fresh weight and root dry weight. Hence the drought tolerant genotypes identified in this study can be effectively utilized as a donor for drought tolerance in drought breeding programmes. The drought screening method i.e., wax petrolatum screening method which focuses on root morphology is found to be reliable and could be used for drought screening at vegetative stage.

Download this article as