USE OF WAX-PETROLATUM LAYERS FOR SCREENING RICE ROOT PENETRATION

The ability of roots to penetrate compacted soils fan be beneficial in avoiding drought stress. However, breeding for root penetration is hindered by the lack of an efficient, reliable screening technique, Our objectives in this study were to develop and evaluate the use of a wax-petrolatum layer system as a reference to measure genotypic variation in root penetration ability of 11 rice (Oryza sativa L.) cultivars from dryland and wetland hydrological origins. The wax-petrolatum layers consisted of 60% wax and 40% petrolatum white, with a penetration resistance strength of 1.4 MPa at 27 degrees C as measured with a soil penetrometer, The wax-petrolatum layers were placed in pots and served as a partial barrier to root growth. Rice cultivars were sown in a randomized complete block design with three replications and grown in a growth chamber. Root penetration ability was measured as the ratio of the number of roots that penetrated the wax-petrolatum layer to the total number of roots, Consistently, rice cultivars from dryland hydrological origins had greater root penetration ability than did cultivars from wetland origins. Root penetration ability ranged from 6 to 26%. Root thickness ranged from 0.9 to 1.5 mm and was positively correlated (r = 0.81, P < 0.001) with root penetration ability. Data indicated that the use of wax-petrolatum layers was an effective technique for measuring differences in root penetration ability.