|Lorence, Argelia - Arkansas State University|
|Henry, Christopher - University Of Arkansas|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2019
Publication Date: N/A
Interpretive Summary: The sustainability of conventional season-long flood irrigation in rice is a concern among rice scientists and growers in the USA. Because of the uncertain patterns of precipitation and the increasing withdrawal from underground aquifers, which are a primary resource for irrigation, the situation is very critical. Practicing reduced irrigation, in the form of alternate wetting and drying (AWD) or furrow irrigation are new practices that are being adopted by rice growers as a means of reducing the demand for irrigation. However, all USA rice varieties were developed for production under conventional season-long flood irrigation management. Thus, determining if there are rice cultivars that are better suited for tolerance to water-deficits is necessary to support future USA rice breeding programs. A three-year study was conducted with a goal to identify cultivar(s) that possess water-deficit stress tolerance trait(s) by evaluating a panel of 15 cultivars under four precisely controlled season-long soil moisture regimes using a subsurface drip irrigation (SDI) system. The panel included a collection of US commercial rice cultivars and selected indica accessions that are adapted to southern US climate. Field trials were conducted using four soil moisture regimes where treatment-1 was fully saturated (field capacity, FC), and the treatment-4 was just above the wilting point. Two soil moisture points were selected in between as treatment-2, and treatment-3. The three-year data supports that SDI is a viable and effective method for germplasm evaluation at pre-defined targeted water-deficit stress levels. On average, the total amount of irrigation applied in the most saturated treatment was 68.98 ha-cm/ha compared to 36.34 ha-cm/ha in the greatest water deficit treatment. The study revealed that average soil moisture stress had a significant impact on yield and yield components (e.g. seed length, seed width, seed thickness, thousand kernel weight). It was interesting to note that days to maturity was not significantly affected by irrigation treatments. On average water-deficit stress treatments also reduced plant height (91 cm to 79 cm), delayed heading dates (89 days to 93 days), and reduced grain yield per plant (26.5 g to 14.4 g) compared to the FC treatment. Based on our analysis, Teqing, Saber, Rondo, Francis, and PI 312777 were identified as cultivars for AWD breeding because they contain traits that could be useful in providing tolerance for irrigation stress in rice. Furthermore, two mapping populations were identified as suitable candidates for deficit water-stress QTL/gene discovery.
Technical Abstract: Access to irrigation resources is becoming more limited, thus the season-long flooding of rice is being replaced by more sustainable irrigation schemes such as alternate wetting and drying (AWD). US rice varieties have been developed for production under permanent flood irrigation and therefore it is crucial to identify germplasm tolerant to reduced irrigation practices for future breeding purposes. The goal of this study was to test the efficacy of a subsurface field drip irrigation (SDI) method for maintaining desired soil moisture levels that could be used to evaluate rice germplasm for water stress tolerance and water productivity (WP). A panel of 15 cultivars including Tropical japonica and Indica rice was evaluated over three consecutive years for phenological and agronomic traits under four soil moisture regimes that ranged from field capacity (30% volumetric water content; VWC) to just above the wilting point (14% VWC) in Stuttgart, AR. Each irrigation treatment zone occupied 268 m2, and an average of 69 ha-cm water was applied to the field capacity treatment (Irrigation-1) as compared to 36 ha-cm in the most water deficit treatment (Irrigation-4). SDI was effective in providing a consistent soil moisture gradient in all three years of study. The average soil moisture content influenced several agronomic traits including plant height, days to heading, yield, grain traits such as length, width, thousand kernel weight, and stress indicators including canopy temperature and stress scores for panicles. Regression analysis identified six traits that explained 35% of the model variability for WP, including panicle stress, canopy temperature, growing degree days, plant height, grain chalk, and maturity. However, even with this small panel of germplasm adapted to the southern USA, the variety effect was much more important in the analysis of variance compared to all other effects. Four varieties (PI 312777, Francis, Zhe 733, and Mars) had 10 or more traits with significant slopes for WP indicating that they were responsive to soil moisture levels and offer promise for future breeding efforts. Further, based on response of these varieties that were used to develop five mapping populations, two were identified as excellent genetic resources for water-stress QTL/gene discovery.