INHERITANCE OF LEAF EPICUTICULAR WAX CONTENT IN RICE

Leaf epicuticular wax (EW) is a trait related to drought resistance. Epicuticular wax content is low in rice (Oryza sativa L.) relative to other crops, but great differences among rice cultivars have been observed, as great as 100%. Traditional drought-resistant upland rices have relatively higher EW content than modern irrigated lowland rices. Our objective was to determine the inheritance of leaf EW content and the prospects for increasing EW levels in improved cultivars. Field, screenhouse, and phytotron experiments were conducted to quantify the EW content in eight rice cultivars. Gas-liquid chromatography was used to measure EW in parents, F1 progeny of an eight-parent diallel cross, and two F2 populations. Area under the three highest GLC peaks, corresponding to C29, C33, and C35 hydrocarbons, accounted for > 90% of EW content. General combining ability effects were highly significant and specific combining ability effects were non-significant. Broad-sense and narrow-sense heritability were 0.77 and 0.62, respectively. In an F2 population from a cross between high- and low-EW parents, EW showed a normal distribution. Few recombinants had EW equal to that of the high wax parent, suggesting polygenic inheritance. While EW is a stable and heritable trait, the F2 data indicate that selection on an individual-plant basis in early generations would not be very effective. Furthermore, measurement is too difficult to be done on large populations and should be confined to identifying promising parents for hybridization.