Genotypic responses of rice to alternate wetting and drying irrigation in the Mekong Delta

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In the Vietnamese Mekong Delta (VMD), alternate wetting and drying (AWD) in rice (Oryza sativa L.) production during the dry season has the potential to reduce greenhouse gas emission and freshwater use. However, its effect on yield compared with continuously flooded systems can vary. To evaluate the effect of AWD on yield and yield-forming processes on genotypes commonly grown in the VMD, field trials over two consecutive dry seasons were conducted at the Loc Troi Group's agricultural research station in the VMD. We observed a significant yield reduction, 7% on average, across all varieties grown under AWD. Analysis of yield components showed that under AWD, genotypes on average produced more tillers, but fewer spikelets, suffered greater spikelet sterility and had a lower 1000 grain weight. The size of this effect differed between dry seasons. Accordingly, we were able to identify and characterize genotypes better suited to AWD. We also could relate shifts in sink-source relationships to the overlap of drying events and key phenological stages other than flowering. Our study shows how successful implementation of AWD requires adaptation to both environment and genotype.

Screening of barley germplasm for drought tolerance based on root architecture, agronomic traits and identification of novel allelic variants of HVA1

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Drought is a major constraint for barley production as it is normally cultivated in rainfed and marginal areas lacking optimum productivity. The domestication bottleneck and further selection pressure have resulted in reduced genetic diversity in barley. Genebank germplasm holds a huge potential for identifying new alleles for stress tolerance. In the present study, a diverse set of 214 accessions from Indian National Genebank were screened for drought tolerance in hydroponics and field conditions. Analysis of variance revealed a significant effect of drought on root architecture, relative water content, membrane stability index, chlorophyll content, plant height, and yield attributes. Cumulative stress response in terms of better root phenotype, physiological and agronomic traits showed accessions IC113045, EC578521, IC582699, EC492318, EC578711, EC667420, IC393980 and IC594943 as most promising donors for breeding programmes in drought-prone areas. Further allelic variation of candidate gene, Hordeum vulgare aleurone 1 (HVA1), and its promoter sequence was studied in a subset of drought-tolerant and -susceptible accessions. The HVA1 gene showed six SNPs and one indel in the genic regions whereas three SNPs and one indel in promoter. Two alleles of HVA1 gene, one in exotic and other in indigenous accession, were found to be associated with drought tolerance. These results were confirmed by qRT-PCR analysis exhibiting significant increase in transcript abundance of HVA1 in drought-tolerant accessions in comparison with susceptible accessions, thereby highlighting its possible role in imparting drought tolerance. The study helped identify genetic resources for drought tolerance in barley and unravelled new alleles of HVA1.

Transmission of photosynthetically active radiation and the productivities of soybean and maize in agroforestry systems

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In integrated crop-livestock-forestry (ICLF) systems, an agroforestry model, the forestry component influences the distribution of photosynthetically active radiation (PAR) and alters grain productivity. The aim of this study was to evaluate the effects of systematic and selective thinning of eucalyptus stands on the productivity of soybean and maize grown. The randomized block-designed experiment comprised three treatments, namely crops grown under full sunlight (CFS) and in ICLF plots subjected to systematic and selective thinning to leave single-row (ICLFS) and triple-row (ICLFT) tree configurations. Soybean and maize were planted in succession between the tree stands and PAR incidence/transmittance and crop productivities were evaluated in the north and south sun-exposed faces of the plots during three cultivation cycles after thinning. In comparison with CFS, PAR transmittance in the ICLF systems decrease varied according to the time of day, period of the year, distance of the sampling position from the trees, the sun-exposed area (north and south faces) and time after thinning. Soybean productivities in ICLFS were similar to those of CFS in the first and second crop cycles, but significantly lower (p < 0.05) in the third crop cycle. In the ICLFT system, soybean productivity was similar to that of CFS in the second crop cycle but significantly lower in the first and third crop cycles. With regard to the maize crop, productivities decreased in the order CSF > ICLFS > ICLFT in all cultivation cycles. Our results showed that PAR transmittance and soybean/maize productivities were positively influenced by thinning of eucalyptus stands, particularly in ICLFS system.

Current status of global rice water use efficiency and water‐saving irrigation technology recommendations

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Rice has a high water requirement, but water use efficiency (WUE) in rice has always been low, and the status of rice WUE and the factors influencing it in various countries around the world is currently unclear. Therefore, this paper collected 56 articles from 2000 to 2022, through which WUE data from different countries and different provinces in China were collated, and the effects of various water-saving irrigation technologies on WUE of rice and irrigation water use were analysed using the method of Meta-analysis. The results of this paper show that rice WUE is low in most countries, with the lowest WUE of 0.28 kg/m3 in Thailand and the highest WUE of 1.25 kg/m3 in Bangladesh among the countries included in this study, and flood irrigation is used in most countries. Compared to flood irrigation, all water-saving irrigation involved can increase rice WUE and reduce irrigation water input, alternate wet and dry irrigation (W1), and controlled irrigation (W2) were able to increase the WUE of rice by 49.86%, 84.74%, and reduce the irrigation water input by 36.55%, 39.55% respectively. Among the six types of water-saving irrigation input, dry cultivation (W3) had the most significant effect on increasing WUE and reducing irrigation water, reaching 2.02 times and 67.53%, respectively. Based on the annual rainfall (R) and the application of water-saving irrigation in Asia, sub-regionally applicable water-saving irrigation technologies are recommended. W3 is recommended when R <200 mm, W2 is recommended when 200 mm < R < 800 mm, and W1/W2/shallow alternate wet and dry irrigation (W5) is recommended when R >800 mm. According to the data collected in this paper, W1, W2, W3, and W5 can save 3.40 × 1011 m3, 3.78 × 1011 m3, 2.52 × 108 m3, 2.22 × 1011 m3 of irrigation water, respectively. Based on the calculations in this paper, different water-saving irrigation techniques can save 3.50 × 1011 m3 of water in Asia according to the recommendations. To promote water-saving irrigation technology, countries need to formulate policies to ensure the development of water-saving irrigation technology, raise farmers' awareness of water conservation, and provide training and financial support. Promoting the use of different water-saving irrigation technologies for different regions can significantly reduce irrigation water and increase the WUE of rice, which is important in addressing the challenges of global water scarcity.

Cover crop water consumption: Analysing performance of the agrometeorological model for the calculation of actual evapotranspiration (AMBAV) in a container experiment

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Due to anthropogenic climate change, cover crop water consumption in winter could potentially increase drought stress for a succeeding crop. Simulation of cover crop evapotranspiration (ET) losses could be a tool for farmers to make smart management decisions. In Germany, the model AMBAV is used by the German Meteorological Service (DWD) to advise farmers in irrigation management. We compared measured ET of phacelia (Phacelia tanacetifolia), oilseed radish (Raphanus sativus var. oleiformis) and white mustard (Sinapis alba) cultivated in a container experiment with simulated data and conducted a sensitivity analysis to identify the meteorological and crop-specific parameters, which had the strongest effect on simulated ET. In general, measured ET exceeded simulated ET. Different statistical criteria showed that AMBAV performed best for the simulation of evaporation from a bare soil surface. Model performance was also strongly influenced by the irrigation regime in the container experiment. However, the sensitivity analysis showed that changes in irrigation hardly influenced simulated ET. We recommend optimization of the model for irrigated agriculture. Furthermore, we identified temperature and humidity as the most important meteorological and leaf area index as the most important crop-specific parameter for ET simulations with AMBAV. Since farmers' management decisions depend on the accuracy of ET simulations, they should be aware that even small regional deviations of meteorological conditions and soil cover can significantly affect model predictions.

Separate or combined effects of soil compaction and/or drought on gas exchange, chlorophyll fluorescence and physiological traits of maize (Zea mays L.) hybrids

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In the natural environment, plants are subjected to simultaneous or sequential presence of various abiotic and/or biotic stresses, including soil compaction and soil drought. The effects of these stresses tested separately are relatively well understood, but still little is known about their simultaneous effects on plants. Our research involved four single hybrids of maize differing in their degree of susceptibility to soil compaction and drought. We investigated the effects of low and high soil compaction under optimal irrigation (LI, HI) and under three-week long soil drought (LD, HD), on the gas exchange (Pn, E, gS, Ci) and chlorophyll fluorescence parameters (F 0, F m, F v, F v/F m), total leaf area (LA), leaf greening (SPAD), leaf water deficit (WD), leaf water potential (ψ) and membrane injury (MI). The plants experiencing high soil compaction (HI) showed a decrease in all parameters of gas exchange (Pn, E, gS, Ci), leaf area (LA), leaf greening (SPAD) and the maximal quantum efficiency of PSII (F v/F m) in comparison with plants growing in non-compacted soil (LI). An increase was observed in the other fluorescence parameters, i.e., F 0, F m and F v and leaf WD, ψ and MI in HI vs. LI variants. In the plants exposed to drought (LD, HD), the changes in the measured traits were greater, especially for the sensitive hybrids P-8400 and NS-3023, than for the plants from LI treatment. A significant interaction between the degree of stress susceptibility and relative trait change was observed for practically all of the measured features. Moreover, in the short recovery period after the end of drought, the measured traits in LD and HD plants did not fully return to the control level, especially in the case of the sensitive hybrids (P-8400 NS-3023). The physiological reaction of maize hybrids to soil compaction and/or soil drought indicated the genetically determined variability of tolerance to those stresses. Significant correlation between RTC and stress susceptibility indexes (S-SI) provided suitable criteria for the hybrid selection. Also, our results showed the plasticity and capability of maize hybrids to respond to environmental conditions.

Genetic erosion within the Fabada dry bean market class revealed by high‐throughput genotyping

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The Fabada market class within the dry beans has a well-differentiated seed phenotype with very large white seeds. This work investigated the genetic diversity maintained in the seed collections within this market class and possible genetic erosion over the last 30 years. A panel with 100 accessions was maintained in seed collections for 30 years, 57 accessions collected from farmers in 2021, six cultivars developed in SERIDA, and 16 reference cultivars were gathered and genotyped with 108,585 SNPs using the genotyping-by-sequencing method. Filtering based on genotypic and phenotypic data was carried out in a staggered way to investigate the genetic diversity among populations. The dendrogram generated from genotyping revealed 90 lines forming 16 groups with identical SNP profiles (redundant lines) from 159 lines classified as market-class Fabada according to their passport data. Seed phenotyping indicated that 19 lines were mistakenly classified as Fabada (homonymies), which was confirmed in the dendrogram built without redundant lines. Moreover, this study provides evidence of genetic erosion between the population preserved for 30 years and the currently cultivated population. The conserved population contains 54.6% segregation sites and 41 different SNP profiles, whereas the cultivated population has 19.6% segregation sites and 26 SNP profiles. The loss of genetic variability cannot be attributed to the diffusion of modern cultivars, which increase genetic diversity (six new SNP profiles). The results allow for the more efficient preservation of plant genetic resources in genebanks, minimizing redundant accessions and incorporating new variations based on genotypic and phenotypic data.

Genome‐wide association study of soluble solids content, flesh color, and fruit shape in citron watermelon

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Fruit quality traits are crucial determinants of consumers’ willingness to purchase watermelon produce, making them major goals for breeding programs. There is limited information on the genetic underpinnings of fruit quality traits in watermelon. A total of 125 citron watermelon (Citrullus amarus) accessions were genotyped using single nucleotide polymorphisms (SNPs) molecular markers generated via whole-genome resequencing. A total of 2,126,759 genome-wide SNP markers were used to uncover marker-trait associations using single and multi-locus GWAS models. High broad-sense heritability for fruit quality traits was detected. Correlation analysis among traits revealed positive relationships, with the exception of fruit diameter and fruit shape index (ratio of fruit length to fruit diameter), which was negative. A total of 37 significant SNP markers associated with soluble solids content, flesh color, fruit length, fruit diameter, and fruit shape index traits were uncovered. These peak SNPs accounted for 2.1%–23.4% of the phenotypic variation explained showing the quantitative inheritance nature of the evaluated traits. Candidate genes relevant to fruit quality traits were uncovered on chromosomes Ca01, Ca03, Ca06, and Ca07. These significant molecular markers and candidate genes will be useful in marker-assisted breeding of fruit quality traits in watermelon.

Detection of a PCR‐based mating type for native intraspecific Beauveria bassiana isolates

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This study developed a PCR-based mating-type analysis of 30 intraspecific Beauveria bassiana isolates after ITS phylogenetic analysis. Out of 30 isolates, only 11 B. bassiana isolates, viz., Bb4, Bb5, Bb11, Bb18, Bb19, Bb20, Bb23, Bb25, Bb27, Bb28, and Bb29, exhibited amplification of the mating-type loci and were thought to be heterothallic. All of these isolates, with the exception of Bb20, had MAT1 mating-type amplification. All these 11 isolates were clustered together with the MAT1- and MAT2-specific reference strains of B. bassiana in the maximum likelihood phylogenetic analysis of mating-type genes (IFO 31953 and IFO 31676, respectively). Although the PCR products obtained by the mating-type assay were short, the phylogenetic trees of the mating-type genes gave better resolution than that of the ITS region. Understanding the mating type of fungi can clarify the biological species concept and the identification of sex-related genes in fungi without the presence of teleomorphs. So, combining phylogenetic, developmental, and mating research on each teleomorph specimen has the potential to clarify the systematics of Beauveria species.