The relationship between biomass production and N2 fixation under drought‐stress conditions in peanut genotypes with different levels of drought resistance is not well understood. The objective of this study was to determine the effect of drought on biomass production and N2 fixation by evaluating the relative values of these two traits under well watered and water‐stress conditions. Twelve peanut genotypes were tested under field conditions in the dry seasons of 2003/2004 and 2004/2005 in north‐east Thailand. A split‐plot design with four replications was used. Main‐plot treatments were three water regimes [field capacity (FC), 2/3 available soil water (AW) and 1/3 AW], and sub‐plot treatments were 12 peanut lines. Data were recorded on biomass production and N2 fixation under well watered and water‐stress conditions. Genotypic variations in biomass production and N2 fixation were found at all water regimes. Biomass production and N2 fixation decreased with increasing levels of drought stress. Genotypes did not significantly differ in reductions for biomass production, but did differ for reductions in N2 fixation. High biomass production under both mild and severe drought‐stress conditions was due largely to high potential biomass production under well‐watered conditions and, to a lesser extent, the ability to maintain high biomass production under drought‐stress conditions. High N2 fixation under drought stress also was due largely to high N2 fixation under well‐watered conditions with significant but lower contributions from the ability to maintain high nitrogen fixation under drought stress. N2 fixation at FC was not correlated with the reduction in N2 fixation at 2/3 AW and 1/3 AW. Positive relationships between N2 fixed and biomass production of the tested peanut genotypes were found at both levels of drought stress, and the relationship was stronger the more severe the drought stress. These results suggested that the ability to maintain high N2 fixation under drought stress could aid peanut genotypes in maintaining high yield under water‐limited conditions.
Drought stress reduces growth and yield in peanut (Arachis hypogaea L.) and also reduces nitrogen fixation (NF). Peanut production in drought prone areas should be enhanced by the development of cultivars that can fix more nitrogen (N) under drought conditions. The aims of this study were to estimate heritability for NF and to estimate phenotypic and genotypic correlations among traits related to NF with drought‐resistance traits and yield under well‐watered and drought conditions. A total of 140 lines in the F4:7 and F4:8 generations derived from four crosses, parental lines, and a non‐nodulating line as a non‐N2‐fixing reference plant were evaluated in the dry seasons 2005/2006 and 2006/2007. These lines were evaluated in rhizobium inoculated soil without N fertilizer under field capacity (FC) and 2/3 available soil water (AW). Data were recorded for specific leaf area (SLA), SPAD chlorophyll meter reading (SCMR), nodule number (NN), nodule dry weight (NDW), shoot dry weight (SDW), pod dry weight (PDW), total dry weight (TDW), harvest index (HI), and NF. Broad‐sense heritability (h2b) and narrow‐sense heritability (h2n) estimates for NF under FC and 2/3 AW were in the same ranges (h2b = 0.84 to 0.98 and h2n = 0.29 to 0.39). Positive relationships between NF under FC and 2/3 AW (r = 0.73, P ≤ 0.01) indicated that selection for the lines that fixed high N under well‐watered conditions should produce lines that fixed high N under drought conditions. Selection for NF under drought conditions might be more effective in improving yield because of a higher correlation between NF and PDW (rG = 0.43, P ≤ 0.01) under drought conditions than under FC (rG = 0.13). The use of SCMR and SLA as surrogate traits for NF would be less effective than direct selection because of weak correlations between these traits and NF.
ABSTRACT:Fertilizer treatments consisting of cyanobacteria blue-green algae (BGA, Anabaena sp.) combined with nitrogen, phosphorus, and potassium were compared with untreated control rice variety Chainat 1 in greenhouse and field experiments from December 2011 to March 2012. In the greenhouse experiment, application of BGA resulted in significantly higher phosphorus and potassium in seeds compared with the untreated control. BGA significantly increased seed weight, and the difference was 16% compared to 47% between application of NPK 16-16-8 + NPK 46-0-0 (125 kg/ha) of chemical fertilizer and untreated control. In field experiments, the differences between BGA and untreated control for nitrogen, phosphorus, and potassium in seeds and straws were not significant, and application of NPK 16-16-8 + NPK 46-0-0 of chemical fertilizer was highest for nitrogen, phosphorus, and potassium in seeds and straws. Application of NPK 16-16-8 + NPK 46-0-0 of chemical fertilizer gave the highest straw dry weight, total dry weight, and seed weight, but the treatments gave similar 1000-seed weight. Application of BGA clearly increased growth and yield of rice in a greenhouse, but the effects were not clear in the field. This information is useful for organic rice production.
Indigenous rice is worth conserving as it possesses many important traits such as good table quality for consumers, resistance to biotic and abiotic stresses and, especially, quality of starch. The objectives of this study were to evaluate indigenous rice accessions collected in Northeast Thailand and select the superior accessions for further improvement of indigenous rice. Forty indigenous rice accessions were evaluated in a pot experiment in a split-plot design with completely randomized arrangement of the treatments and four replications for two years in 2014 and 2015. Main plots were two water regimes, including well-irrigated treatment and early season drought treatment; the subplots included 40 indigenous rice accessions. Well-irrigated treatment was higher than early season drought condition in terms of plant height, number of tiller per plants, number of ears per plant, number of unfilled grains per ear, grain weight per plant, straw weight per plant and shoot dry weight per plant; drought treatment was higher than irrigated treatment in terms of the number of filled grains per plant, 1000-grain weight and root dry weight; whereas these two types of treatment showed no differences in terms of the number of tillers/plant at 30 days after emergence and harvest index. The superior genotypes for each trait and the genotypes with better drought tolerance index were identified.
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