Chlorophyll stability during drought might be a promising criterion for selection for drought resistance in peanut. The study describes two field trials conducted at Khon Kaen University, Thailand which investigate genotype × drought interactions in a wide range of peanut germplasm in general and assess the relationship between chlorophyll stability and genotypic performance in particular, under drought. Two field experiments (during 2003/2004 and 2004/2005 dry seasons) were conducted in a split plot design with three water regimes [field capacity, 2/3 available water (AW) and 1/3 AW] as main, and 12 peanut genotypes as subtreatments, replicated four times. Observations on total dry matter (TDM), chlorophyll density (ChlD) (chlorophyll content per unit leaf area), chlorophyll content (chlorophyll content per plant) and SPAD chlorophyll meter readings (SCMR) were recorded at 30, 60 and 90 days after emergence. Transpiration (T) and transpiration efficiency (TE) were computed using the data on amount of water input and TDM. Drought stress significantly reduced TDM, T and chlorophyll content across genotypes but significantly increased TE and ChlD in peanut. However, there were significant differences among genotypes for TE and chlorophyll parameters. The genotype × drought interaction effects for chlorophyll characters (content and density) were not significant suggesting a strong genetic effect. The correlation coefficients between TDM and chlorophyll content (r = 0.51, P = 0.01 to r = 0.91, P = 0.01) and between TE and ChlD (r = 0.46, P = 0.05 to r = 0.77, P = 0.01) were positive and significant. These findings suggest that chlorophyll parameters are strongly linked with drought tolerance in peanut. There were highly significant and positive relationships between ChlD and SCMR (r = 0.67, P = 0.01 to r = 0.93, P = 0.01), between SCMR and TE (r = 0.41, P = 0.05 to r = 0.80, P = 0.01) suggesting that SCMR could be used as a tool for rapid assessment of relative chlorophyll status in peanut genotypes as well as for the indirect selection of drought tolerance in peanut.

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Lowland and upland rice are the two most important rice ecotypes and are grown under different ecosystems of contrasting soil water conditions. The study aimed to characterize root morphological, anatomical, and architectural traits and shoot physiological traits related to agronomic traits in Myanmar lowland and upland rice under drought conditions. Drought experiments were conducted in the field and in the greenhouse. The reduction in root traits under drought was observed in both lowland and upland rice except for the stele and xylem area. Stele area and xylem area were increased under drought in lowland rice while stele area in upland rice was decreased and was not changed in the xylem area. A positive relationship between agronomic traits and root traits of lowland rice was observed including the total number of nodal roots, root number per tiller, and a negative relationship in lateral root density more than anatomical traits. While upland rice illustrated the relationship between root anatomical traits and agronomic traits. In addition, a negative contribution to biomass by photosynthesis rate, stomatal conductance, and transpiration rate was observed in lowland and upland rice. These findings can help improve drought tolerance in rice by selecting the optimal root trait for each rice ecosystem.

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Background: High-throughput phenotyping systems containing non-destructive and non-invasive characterizations of phenotypic traits throughout the whole life cycle of plant development have prevailed over the conventional method. The aim of this investigation was to evaluate the phenotypic characteristics of indica rice genotypes using RGB high-throughput phenotyping over the whole life cycle in relation to biomass and yield components. Results: Plant canopy width, canopy height and leaf area values of the rice cultivars RD41, Pathumthani1 (PT1), Homchonlasit, IR64, Riceberry and RD43 were measured using RGB imagery estimation together with actual measurements at 45, 60, 75, 90, 105 and 120 DAP. Canopy width and canopy height values obtained from actual measurements were linearly related to RGB-estimated values in all rice cultivars with r = 0.87-0.93 and r = 0.90-0.99, respectively. Interestingly, a positive relationship between plant projected area from RGB imagery and leaf area measurement was observed, especially at the vegetative stage (r = 0.93- 0.99). At harvest, a positive relationship between aboveground biomass and total yield was also found (R2 = 0.44). Conclusion: The agronomical traits and plant characterizations of RD41, PT1, Homchonlasit, IR64, Riceberry and RD43 were validated over the whole life cycle of rice crops in the present investigation. Based on this study, we confirm that high-throughput phenotyping data collection should overcome conventional measurements due to its non-destructive, rapid, and automated production of big data and high accuracy in indica rice crops.