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 hi ndered 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 fr om dryland and wetland hydrological origins. The wax-petrolatum layers consisted of 60% wax and 40% petrolatum white, with a penetration res istance strength of 1.4 MPa at 27 degrees C as measured with a soil pe netrometer, The wax-petrolatum layers were placed in pots and served a s a partial barrier to root growth. Rice cultivars were sown in a rand omized complete block design with three replications and grown in a gr owth chamber. Root penetration ability was measured as the ratio of th e number of roots that penetrated the wax-petrolatum layer to the tota l number of roots, Consistently, rice cultivars from dryland hydrologi cal origins had greater root penetration ability than did cultivars fr om wetland origins. Root penetration ability ranged from 6 to 26%. Roo t 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 measu ring differences in root penetration ability.