Relationship of agro-morphological traits to water use efficiency of irrigated lowland rice varieties under screenhouse condition

Rice (Oryza sativa L.) is the only cereal food crop that grows in different hydrological conditions. As staple food in the Philippines, it is cultivated in different parts of the country from irrigated to rainfed lowland, upland, cool elevated, flood-prone, and saline ecosystems. Among these ecosystems, irrigated lowland has highest production, however its productivity is threatened by increasing water scarcity. Crop water use efficiency is widely used to evaluate productivity in terms of water use. However, currently, there are limited studies in this area particularly on the relationship of agro-morphological traits to water use efficiency which can be used by breeders to improve rice water use efficiency. Hence, this study aimed to identify the relationship of agro-morphological traits to biomass production, evapotranspiration, and water use efficiency of irrigated lowland rice varieties, and to identify growth phase and variety with highest water use efficiency. Three irrigated lowland rice varieties were grown in the pots with 40cm x 30cm (row x hill) planting distance under screenhouse condition. This was laid-out in split-plot in Randomized Complete Block Design with growth phase as main plot and variety as sub-plot, replicated three times. Based on the result, broad leaf contributed in decreasing evapotranspiration and increasing biomass and water use efficiency. Broad leaves have higher boundary layer and contribute to better covering of soil surface both of which reduce evapotranspiration, and contribute to higher light interception for higher biomass production, hence high water use efficiency. Other traits such as long leaf, high spikelet fertility, heavy grain, and early maturity also contributed to reduction of evapotranspiration and improvement of water use efficiency. Hence, these traits might have the potential to improve water use efficiency of irrigated lowland rice varieties. Among growth phases, reproductive phase had highest water use efficiency due to higher rate of increase in biomass and lower rate of increase in evapotranspiration than ripening phase. NSIC Rc202H with broadest leaves and lowest cumulative evapotranspiration had highest water use efficiency than NSIC Rc222 and PSB Rc18.