Drought Tolerance Indices Research Articles

A high-throughput approach for quantifying turgor loss point in grapevine

Quantifying drought tolerance in crops is critical for agriculture management under environmental change, and drought response traits in grape vine have long been the focus of viticultural research. Turgor loss point (πtlp) is gaining attention as an indicator of drought tolerance in plants, though estimating πtlp often requires the construction and analysis of pressure-volume (P-V) curves which are very time consuming. While P-V curves remain a valuable tool for assessing πtlp and related traits, there is considerable interest in developing high-throughput methods for rapidly estimating πtlp, especially in the context of crop screening. We tested the ability of a dewpoint hygrometer to quantify variation in πtlp across and within 12 clones of grape vine (Vitis vinifera subsp. vinifera) and one wild relative (Vitis riparia), and compared these results to those derived from P-V curves. At the leaf-level, methodology explained only 4–5% of the variation in πtlp while clone/species identity accounted for 39% of the variation, indicating that both methods are sensitive to detecting intraspecific πtlp variation in grape vine. Also at the leaf level, πtlp measured using a dewpoint hygrometer approximated πtlp values (r2 = 0.254) and conserved πtlp rankings from P-V curves (Spearman’s ρ = 0.459). While the leaf-level datasets differed statistically from one another (paired t-test p = 0.01), average difference in πtlp for a given pair of leaves was small (0.1 ± 0.2 MPa (s.d.)). At the species/clone level, estimates of πtlp measured by the two methods were also statistically correlated (r2 = 0.304), did not deviate statistically from a 1:1 relationship, and conserved πtlp rankings across clones (Spearman’s ρ = 0.692). The dewpoint hygrometer (taking ∼ 10–15 min on average per measurement) captures fine-scale intraspecific variation in πtlp, with results that approximate those from P-V curves (taking 2–3 h on average per measurement). The dewpoint hygrometer represents a viable method for rapidly estimating intraspecific variation in πtlp, and potentially greatly increasing replication when estimating this drought tolerance trait in grape vine and other crops.

Advancing rice breeding for drought tolerance: a comprehensive study of traditional and mutant lines through agronomic performance and drought tolerance indices

BackgroundDrought stress is a critical challenge to rice production, necessitating the development of drought-tolerant genotypes. This study aimed to evaluate the drought tolerance of rice genotypes, including traditional parental lines (Hashemi, Khazar, Fajr, and Tarom Mahalli) and their corresponding mutant lines, under normal and drought stress conditions.MethodsAgronomic traits such as plant height, spike number, spike length, seed fertility, and yield were analyzed under both conditions. The performance of these genotypes was further assessed using drought tolerance indices. Statistical methods including cluster analysis and principal component analysis (PCA) were applied to identify the most resilient genotypes.ResultsMutant lines demonstrated superior drought resilience compared to their parental counterparts. Specifically, genotypes like TM-230-VE-7-5-1, TM-B-2-1-E, and HM-250-7-6 exhibited higher yields and better stability of key traits under stress conditions. Cluster analysis and PCA emphasized the strong performance of TM-230-VE-7-5-1, which emerged as the most drought-tolerant genotype, excelling across various drought tolerance indices.ConclusionsThe selected mutant lines, particularly TM-230-VE-7-5-1, showed significant potential for breeding programs aimed at improving drought tolerance in rice. These findings have substantial implications for enhancing rice production in drought-prone regions, contributing to sustainable agricultural practices.

Investigating drought tolerance in four Argania spinosa provenances through morpho-physio-biochemical traits

ABSTRACT Drought stress significantly threatens plant ecosystems, particularly amid climate change. Understanding the mechanisms of plant resilience is essential for developing strategies to mitigate water scarcity effects on agroforestry. This study evaluated morphological, physiological and biochemical traits in Argania spinosa seedlings from four provenances (Berkane (BRK), Essaouira (ESS), Agadir (AGD) and Bouizakarne (BZK)) subjected to severe drought for three weeks. The results showed significant inter-provenance variation in the traits examined. Root dry biomass increased markedly across all provenances, with the highest increase observed in BZK (117.9%). Leaf water potential significantly decreased under drought stress, but relative water content (RWC) remained stable. Proline accumulation was significant in stressed seedlings, especially in ESS (163.4%), while total soluble sugars significantly increased only in BRK (26.6%). All provenances showed a significant reduction in chlorophyll a and b, except for BRK. Correlations among all studied traits varied significantly in both number and significance between drought stress and non-stress conditions. Canonical discriminant analysis revealed distinct separation among the provenances, indicating intra-species variability in drought responses. Key traits like dry biomass, collar diameter, basic leaf water potential, RWC and proline were identified as important indicators of drought tolerance, suggesting their utility in selecting the most resilient A. spinosa provenance.

Modeling Root Development of Rice (Oryza sativa L) under Varying Drought Stress

In the current era, where drought occurrences are frequent and devastating, extensive study on drought tolerance mechanisms is imperative. Root growth under water stress is a key indicator of drought tolerance. Modeling a crop's root-length under such conditions aids in predicting seminal root length (SRL) and, consequently, its tolerance level. Under consecutive stress using Poly-ethylene-glycol (PEG), root length of a landrace originating from the drought-prone area of West Bengal, India was measured through image analysis and then mathematically modulated using an equation. The highest root length under stress was predicted at 6% PEG stress which aligned with the experimental readings. On the 15th day of stress, predicted SRL values were 104.67mm and experimental values were 90.00mm. Despite some over and underestimations with a low root mean square error of 14.68 mm, the equation provides insight into root elongation trends under various stress levels, offering a basis for predicting SRL and yield capabilities under water stress for diverse crop species.

Screening of drought tolerance indices for selection of resistance wheat (Triticum aestivum L.) landraces under drought stress conditions

Abstract During the cropping season 2016-2017, an experiment was conducted in a split plot design to study the response of 25 wheat genotypes to drought stress under irrigated and minimal irrigation conditions. Different drought tolerance indices for 25 bread wheat (Triticum aestivum L.) genotypes were evaluated. The calculation drought tolerance indices was based on the grain yield of wheat under irrigated and water stress conditions. The result indicated a significant effect of drought stress on the yield of different wheat genotypes based on mean values of different drought tolerance indices. Among the studied different indices, mean productivity (MP), stress tolerance index (STI), and geometric mean productivity (GMP) were more efficient to discriminate between drought sensitive and drought tolerant genotypes based on the calculation of correlation coefficient and multivariate analysis. Twenty-five genotypes were classified into tolerant and susceptible groups through drought tolerance indices using cluster analysis. Among the genotypes, C-306, WH 1236, WH 1235, and GW 477 having higher yields under drought conditions which showing their stability under stress conditions. The most yield stable genotypes under adverse environment were identified by multivariate analysis of drought tolerance indices individually or in combination. From the result, we concluded that GMP, MP and STI are more efficient drought tolerance indices among other indices to identify stable genotypes under stress conditions.

Stress-Responsive Gene Expression, Metabolic, Physiological, and Agronomic Responses by Consortium Nano-Silica with Trichoderma against Drought Stress in Bread Wheat

The exploitation of drought is a critical worldwide challenge that influences wheat growth and productivity. This study aimed to investigate a synergistic amendment strategy for drought using the single and combined application of plant growth-promoting microorganisms (PGPM) (Trichoderma harzianum) and biogenic silica nanoparticles (SiO2NPs) from rice husk ash (RHA) on Saudi Arabia’s Spring wheat Summit cultivar (Triticum aestivum L.) for 102 DAS (days after sowing). The significant improvement was due to the application of 600 ppm SiO2NPs and T. harzianum + 600 ppm SiO2NPs, which enhanced the physiological properties of chlorophyll a, carotenoids, total pigments, osmolytes, and antioxidant contents of drought-stressed wheat plants as adaptive strategies. The results suggest that the expression of the studied genes (TaP5CS1, TaZFP34, TaWRKY1, TaMPK3, TaLEA, and the wheat housekeeping gene TaActin) in wheat remarkably enhanced wheat tolerance to drought stress. We discovered that the genes and metabolites involved significantly contributed to defense responses, making them potential targets for assessing drought tolerance levels. The drought tolerance indices of wheat were revealed by the mean productivity (MP), stress sensitivity index (SSI), yield stability index (YSI), and stress tolerance index (STI). We employed four databases, such as BAR, InterPro, phytozome, and the KEGG pathway, to predict and decipher the putative domains in prior gene sequencing. As a result, we discovered that these genes may be involved in a range of important biological functions in specific tissues at different developmental stages, including response to drought stress, proline accumulation, plant growth and development, and defense response. In conclusion, the sole and/or dual T. harzianum application to the wheat cultivar improved drought tolerance strength. These findings could be insightful data for wheat production in Saudi Arabia under various water regimes.

Exploring the usefulness of drought tolerance indices in screening of maize inter-racial derivatives

Abstract Among all the abiotic factors affecting maize yield, drought stress is the most destructive one. Since drought tolerance is a complicated trait that is difficult to quantify, screening for stress involves measuring the effects of stress on several traits, most notably plant yield. Selection using the drought tolerance indices is an easy way to identify the stable and tolerant genotypes based on yield performances alone. The current study aims to identify suitable maize hybrids with high drought tolerance. A total of 30 maize-teosinte hybrids and 3 checks were raised under optimal and water-stressed environments and were screened using twelve different drought tolerance indices. It was observed that the inter-racial hybrids viz., G24, G27, and G29 were better than the drought tolerant Zea mays ssp. mays check C3 for yield and most of the indices. The indices STI, TOL, GMP, MP, YI, DI, SSPI, K1STI, and K2STI were observed to be significantly correlated with yield under stress and optimal environments. Based on the yield both environments, the genotypes were classified under four groups, with Group A consisting of genotypes with high yields under both environments. The indices Stress Tolerance Index (STI), Geometric Mean Productivity (GMP), Yield Index (YI), and Modified Stress Tolerance Index (K2STI)were identified for their ability to discriminate Group A from the other genotypes and these indices could be utilized to screen for drought tolerance with high yield.Component Analysis revealed two principal components contributing up to 98.15 percent of the cumulative variation. The PCA biplot identified the hybrids viz., G24, G27, G14, G19, and G25 as tolerant ones. Based on the index scores, the hybrids viz., G27, G29, G17, G20,and G24were identified as the top-ranking genotypes, with high and more stable yields under both stress and optimal environments. Keywords: Drought index, maize, 3D plot, inter-racial hybrids, teosinte

Screening of Ecotypes and Construction of Evaluation System for Drought Resistance during Seed Germination in Kudouzi (Sophora alopecuroides)

Drought is a major limiting factor in the cultivation of Sophora alopecuroides in China’s arid and semi-arid regions. This study aimed to identify drought-resistant S. alopecuroides ecotypes and explore key drought tolerance indicators during germination by simulating drought conditions with a 10% PEG-6000 solution, using pure water as a control. Determination of seven germination indicators for S. alopecuroides, including germination rate (GR), germination energy (GE), germination index (GI), vigor index (VI), promptness index (PI), fresh weight (FW), and dry weight (DW), was conducted. Principal component analysis (PCA), membership function, cluster analysis, and linear regression were employed to comprehensively evaluate the drought resistance of thirty-five S. alopecuroides ecotypes. The results showed that drought stress caused reductions in six of the seven indicators across all ecotypes, except for DW, compared to the control. Correlation analysis revealed varying relationships among the indicators, with most showing significant or highly significant correlations. PCA reduced the seven indicators to two independent comprehensive factors, with a cumulative contribution rate of 83.99%. Based on the D-value and cluster analysis, the thirty-five ecotypes were ranked for drought resistance and classified into four categories. The top five drought-tolerant genotypes during the germination stage were identified as Yutian, Alar, Jinghe, Baoding, and Guyuan. Moreover, the stepwise regression model was established and demonstrated that GR, GE, PI, FW, and DW are key indicators for screening and identifying drought-resistant S. alopecuroides ecotypes. This study offers a comprehensive and reliable method for evaluating drought resistance in S. alopecuroides ecotypes and provides a reference for selecting ecotypes for artificial cultivation in Northwestern China.

Genome-wide association mapping and genomic prediction of water deficit stress tolerance indices in spring bread wheat

Genome-wide association mapping (GWAM) is crucial for identifying the genetic architecture of quantitative traits, such as drought tolerance indices in bread wheat. This study aims to identify Marker-Trait Associations (MTAs) and genes related to drought tolerance indices in wheat. Seven drought tolerance indices were calculated based on grain weight per spike under field drought stress (FDS) and field non-stress (FNS) conditions. These indices included mean productivity (MP), geometric mean productivity (GMP), relative drought index (RDI), stress tolerance index (STI), tolerance index (TOL), stress susceptibility index (SSI), and yield stability index (YSI). Genotyping of the samples was performed using single nucleotide polymorphism (SNP) markers. A total of 96 MTAs were identified for the studied indices and conditions FNS and FDS in this experiment, with a threshold of -log10p ≥ 3.0. These included FNS, FDS, GMP, MP, STI, SSI, RDI, and YSI, with 15, 11, 16, 16, 20, 6, 6, and 6 MTAs, respectively. The MTAs identified for the drought tolerance indices GMP, MP, and STI were located on chromosomes 2 A, 3B, and 6 A, respectively. Moreover, this study identified four genes related to the indices, namely “TraesCS2B02G000100,” “TraesCS3A02G000100,” “TraesCS2B02G000200,” and “TraesCS4B02G000100”. These genes play a crucial role in drought tolerance and can be utilized for marker-assisted selection to enhance drought tolerance wheat genotypes.

Eco-Physiological and Genetic Basis of Drought Response Index in Rice—Integration Using a Temperate Japonica Mapping Population

The drought response index (DRI) is an indicator of drought tolerance after adjustment for variation in flowering date and potential yield under well-watered conditions. Using a temperate japonica mapping population of 97 recombinant inbred lines from a cross between Otomemochi (OTM) and Yumenohatamochi (YHM), we evaluated DRI during the reproductive stage under very severe drought in one year and under severe drought in the next year. DRI under very severe drought (−6.4 to 15.9) and severe drought (−3.9 to 8.3) positively correlated with grain dry weight under drought. Three QTLs for DRI were identified: RM3703–RM6911–RM6379 and RM6733–RM3850 both on chromosome 2 in both years combined; and RM8120–RM2615–RM7023 on chromosome 6 in the second year. The latter collocated with putative genes for signaling and defense mechanisms (e.g., PIN1B, BZIP46) revealed by database analysis. Top DRI lines retained root dry weight and had bigger steles. QTL-by-environment interaction had a greater relative contribution than the main effects of QTLs. Comparison with three previous studies revealed that the QTLs for DRI were unique to each experiment and/or population; most of them closely colocalized with reported drought-yield QTLs.

Assessment of growth and biochemical indicators for drought tolerance in maize cultivars

Assessment of growth and biochemical indicators for drought tolerance in maize cultivars

Multi-locus genome-wide association study for grain yield and drought tolerance indices in sorghum accessions.

Drought is a significant factor that causes yield loss in essential cereal crops such as sorghum [Sorghum bicolor (L.) Moench], necessitating the development of drought-tolerant varieties adaptable to various water conditions. This study aimed to pinpoint drought-tolerant sorghum lines and genomic regions for tolerance by utilizing 216 sorghum accessions in stressed and non-stressed environments at two locations. Genetic diversity was evident among accessions in terms of grain yield under different watering regimes. Drought stress indices such as the stress tolerance index, mean productivity, geometric mean productivity, harmonic mean productivity, yield stability index, and yield index were identified as effective measures for selecting drought-tolerant sorghum. Cluster analysis classified genotypes into four groups based on their association with grain yield, highlighting Acc. #28546 and Acc. #216739 as highly drought tolerant across environments. This study identified 32 and 22 quantitative trait nucleotides (QTNs) for drought indices and grain yield under stress and non-stress conditions, respectively, at two locations, with five common QTNs linked to multiple drought indices. Colocation analysis revealed that these QTNs were associated with known stay-green-related quantitative trait loci (QTLs), and 47 putative genes near these QTNs potentially influenced drought tolerance traits. It is suggested that accession selection considers multiple indices for robust evaluation. Understanding the identified genes and their functions provides insights into the genetic mechanisms governing plant responses to drought stress, offering prospects for developing improved drought-resistant sorghum varieties through further genetic research.

Screening and Physiological Responses of Maize Inbred Lines to Drought Stress in South China

The frequent occurrence of localized and seasonal droughts has caused severe economic losses in maize production in South China. To promote sustainable maize production, selecting and breeding drought-tolerant varieties is vital for addressing water scarcity. Drought stress affects all aspects of crop morphological performance. In this study, the morphological performance of 285 maize inbred lines under drought stress was investigated using D-value analysis, correlation analysis, principal component analysis, cluster analysis and stepwise regression analysis. All indicators were significantly different in the regular treatment compared to the drought treatment. Specifically, survival rate, root fresh weight, root dry weight, plant dry weight, root/crown ratio, and plant fresh weight were used as indicators for drought-tolerance evaluation. Furthermore, the drought-tolerant inbred line CML323 and the drought-sensitive inbred line CB2-49-1 were screened by comprehensively evaluating D values. The drought-tolerant inbred line CML323 exhibits higher leaf relative water content, chlorophyll content, proline content, and ascorbate peroxidase and peroxidase activity while having lower malondialdehyde content, consequently demonstrating excellent drought tolerance. This study provides valuable insights into drought-tolerance indicators and reference materials for breeding maize varieties.

Screening Wheat Genotypes for Specific Genes Linked to Drought Tolerance.

Drought stress, which significantly affects growth and reduces grain yield, is one of the main problems for wheat crops. Producing promising drought-tolerant wheat cultivars with high yields is one of the main targets for wheat breeders. In this study, a total of seven drought-tolerant wheat genotypes were screened for the presence of 19 specific drought tolerance genes. The genotypes were tested under normal and drought conditions for two growing seasons. Four spike traits, namely, spike length (SPL), grain number per spike (GNPS), number of spikelets per spike (NSPS), and grain yield per spike (GYPS), were scored. The results revealed that drought stress decreased the SPL, GNPS, NSPS, and GYPS, with ranges ranging from 2.14 (NSPS) to 13.92% (GNPS) and from 2.40 (NSPS) to 11.09% (GYPS) in the first and second seasons, respectively. ANOVA revealed high genetic variation among the genotypes for each trait under each treatment. According to the drought tolerance indices, Omara 007 presented the highest level of drought tolerance (average of sum ranks = 3), whereas both Giza-36 genotypes presented the lowest level of drought tolerance (average of sum ranks = 4.8) among the genotypes tested. Among the 19 genes tested, 11 were polymorphic among the selected genotypes. Omara 007 and Omara 002 presented the greatest number of specific drought tolerance genes (nine) tested in this study, whereas Sohag-5, Giza-36, and PI469072 presented the lowest number of drought tolerance genes (four). The number of different genes between each pair of genotypes was calculated. Seven different genes were found between Omara 007 and Giza-36, Omara 007 and Sohag-5, and Omara 002 and PI469072. The results of this study may help to identify the best genotypes for crossing candidate genotypes, and not merely to genetically improve drought tolerance in wheat.

Integrating genetic assortment and molecular insights for climate-resilient breeding to unravel drought tolerance in cotton

This study addresses the challenges posed by rainfall variability, leading to water deficits during critical stages of crop growth, resulting in a drastic reduction of cotton yield. In a comprehensive evaluation, thirty cotton genotypes, including five Gossypium arboreum (wild) and twenty-five Gossypium hirsutum (cultivated), were grown under rainfed and irrigated conditions. Drought tolerance indices (DTI) were evaluated, categorizing genotypes based on their resilience. Further, in-vitro screening at the seedling stage (20 days) under PEG-induced drought identified tolerant genotypes exhibiting elevated levels of free proline (19.07±5.31 mg.g−100fr.wt.), amino acids (34.59±6.51 mg.g−100fr.wt.), soluble proteins (13.73±2.65 mg.g−1fr.wt.), and glycine betaine (10.95±3.62 mg.g−100fr.wt.), in their leaves, positively correlating (p<0.001) with relative water content (87.70±3.45 %). Molecular analysis using drought-specific simple sequence repeats (SSR) markers revealed significant genetic variability in a cotton genotypes, with lower observed and higher expected heterozygosity. F statistics exposed a higher level of gene flow corresponding to low differentiation among populations. Among the genotypes group, wild GAM-67 and cultivated Deviraj emerged as the most potent, exhibiting the higher DTI and diverse gene pools. Study exhibited higher total gene diversity in drought-tolerant wild GAM-67 (0.8501) and greater expected heterozygosity (0.626) and gene flow (0.6731) in cultivated Deviraj, underlining their robust genetic adaptability to drought conditions. The integrated approach of field evaluations, in-vitro screening, and molecular analyses explained substantial genetic diversity, with the identification of promising genotypes displaying higher drought tolerance indices, elevated levels of stress-related biochemical osmolytes, and pronounced genetic adaptability, thereby contributing to the advancement of breeding initiatives for enhanced drought resilience in cotton.

Exotic alleles from the wild Hordeum spontaneum contribute to drought tolerance and grain quality in modern Hordeum vulgare

Conventional breeding relies on genetic variability in crop germplasm and wild species. This study evaluated 137 barley Recombinant Chromosome Substitution Lines (RCSLs), originating from crossing a drought and salinity-tolerant wild Hordeum spontaneum with the high-quality malting H. vulgare cv. Harrington. The objectives of this work were to i) improve understanding of the genetic diversity and introgression levels in RCSLs using a comprehensive set of high-density single nucleotide polymorphism (SNP) markers; ii) investigate the phenotypic variability of physiological, agronomic, and malting quality traits in RCSLs under rainfed and fully irrigated conditions; iii) unravel the relationship between these traits and the resilience of crops in drought-prone regions; and iv) identify specific SNPs associated with both drought tolerance indices and malting quality traits. Variability in physiological, agronomic, and malting quality traits was examined under rainfed and irrigated conditions, aiming to identify specific SNPs associated with both drought tolerance indices and malting quality traits. Additionally, a subset of three recombinant lines and the parent cv. Harrington was tested in growth chambers under well-watered and water-limited conditions. Agronomic traits were influenced by genotype-by-environment interaction, with notable drought tolerance lines. The grain yield was significantly correlated with yield-related traits and carbon isotope discrimination in grains. Drought stress impacted agronomic and physiological traits, with a strong reduction in leaf gas exchange and chlorophyll and protein content. The H. spontaneum genome introgression into H. vulgare cv. Harrington varied across 137 RCSLs, averaging 13.0 %. Associations between traits and genetic markers were found, particularly for the stress tolerance index in chromosome 1H and for grain quality traits (alfa-amylase, wort color, and protein) in chromosomes 1H, 4H, and 5H. These findings uncovered valuable barley RCSLs that demonstrate drought tolerance, offering promising prospects for breeding programs targeted at improving stress resilience.

Molecular characterization and evaluation of different irrigation regimens on yield and other agronomic traits of some Egyptian wheat cultivars

ABSTRACT The objective of this study was to determine the optimal irrigation needs of six popular Egyptian bread wheat (Triticum aestivum L.) cultivars and to establish baseline effect of reduced irrigation on yield. The varieties included were Sids1, Sids14, Sakha94, Sakha95, Gemmiza12, and Shandawee1. The experiment was conducted at two different locations, Nubaria and Sids Agricultural Research Stations, Egypt over two consecutive seasons, 2020–2021 and 2021–2022. There was a reduction in yield with the decrease in the number of irrigations. However, several cultivars performed better for yield and other traits with one less irrigation than the current irrigation practices in the region. Therefore, the study may help revise irrigation recommendations. Overall, the cultivars Sakha95, Sids1, and Sids14 were taller and had more kernels per spike, higher seed index, and greater grain yield under reduced irrigations and showed the best drought tolerance index. The tested bread wheat cultivars were genotyped using Inter-Retrotransposon Amplified Polymorphism (IRAP) and Start Codon Targeted (SCoT) markers which showed relation among the cultivars. Among the two types of markers, IRAP was better than SCoT markers for reliability and robustness. Among the six cultivars, 58% of the IRAP markers detected polymorphism as compared to 38% with SCoT markers. The two wheat cultivars Sids1 and Sids14, which performed better for important agronomic traits under water stress conditions, could be used as donors for the national wheat breeding program for drought tolerance.

INFLUENCE OF DROUGHT STRESS ON THE FRUIT AND YIELD QUALITY OF THREE DIFFERENT VARIETIES OF TOMATO (Lycopersicum esculentum L.)

Drought impacts various physiological processes in plants, ultimately affecting yield. The study aimed to determine the influence of drought stress on the fruit and yield quality of three different varieties of tomato namely; Rio, Dan Syria and UTC. The plants were subjected to four treatments which were subjected to 80-85% WHC (water holding capacity) (control, T1), 55-60% WHC (light drought stress, T2), 40-45% WHC (moderate drought stress, T3) and 30-35% WHC (severe drought stress, T4) and each replicated three times. The data generated were subjected to Analysis of Variance (ANOVA). According to the findings, Rio outperformed the other varieties in terms of fresh fruit weight (21.59g), fruit pericarp thickness (3.96mm) and drought tolerance index (56.17%) under severe drought conditions. However, under severe drought conditions, the highest average number of fruits (2.33) was produced by the UTC, closely followed by Dan Syria (2). The results also showed that under severe drought stress, Rio outperformed the other varieties in terms of fresh and dry weight of shoot, as well as fresh and dry weight of root (18.82g, 3.47g and 3.34g, 1.29g) closely followed by Dan Syria measuring 12.47g, 1.66g, 3.10g, and 0.62g respectively. Under conditions of severe drought stress, Rio, UTC, and Dan Syria exhibit drought tolerance indices of 56.17%, 37.49%, and 20.44% respectively. These suggest that Rio is the most resilient to drought compared to the other varieties. Therefore, farmers should consider using Rio, which has a high level of drought resistance, as a means to mitigate the impact of drought.

Comprehensive evaluation of drought tolerance of six Chinese chestnut varieties (clones) based on flavonoids and other physiological indexes

Flavonoids are crucial secondary metabolites that possess the ability to mitigate UV damage and withstand both biotic and abiotic stresses. Therefore, it is of immense significance to investigate the flavonoid content as a pivotal indicator for a comprehensive assessment of chestnut's drought tolerance. This study aimed to determine the flavonoid content and drought tolerance-related physiological and biochemical indices of six chestnut varieties (clones) grafted trees—Qianxi 42 (QX42), Qinglong 45 (QL45), Yanshanzaofeng (YSZF), Yanzi (YZ), Yanqiu (YQ), and Yanlong (YL)-under natural drought stress. The results were used to comprehensively analyze the drought tolerance ability of these varieties. The study revealed that the ranking of drought tolerance indices in terms of their ability to reflect drought tolerance was as follows: superoxide (oxide) dismutase (SOD) activity, ascorbate peroxidase (APX) activity, flavone content, catalase (CAT) activity, proline (PRO) content, soluble sugar content, peroxidase (POD) activity, betaine content, flavonol content, hydrogen peroxide (H2O2) content, soluble protein content, superoxide ion (OFR) content, superoxide (ion OFR) production rate, malondialdehyde (MDA) content, chlorophyll content. Through principal component analysis, the contents of flavonoids and flavonols can be used as indicators for comprehensive evaluation of drought tolerance of chestnut. The comprehensive evaluation order of drought tolerance of grafted trees of 6 chestnut varieties (Clones) was: QL45 > QX42 > YQ > YZ > YSZF > YL.

Morpho-physiological and yield traits for selection of drought tolerant Urochloa grass ecotypes.

Drought has become more recurrent and causes a substantial decline in forage yields leading to strain on feed resources for livestock production. This has intensified the search for drought-tolerant forages to promote sustainable livestock production. The objective of this study was to identify drought-tolerant Urochloa grasses and to discern their morpho-physiological and yield traits to water stress as well as the relationship between these traits and indices of drought resistance. The results showed that the ecotypes, water regimes and their interaction significantly influenced all the studied morpho-physiological and yield traits. There was a significant decrease in plant height, number of leaves and tillers, dry matter yield, relative water content, photosystem II and efficiency of photosystem II with an increase in non-photochemical quenching. The principal component analysis revealed that the performance of Urochloa grass ecotypes was different under water sufficient (WS) and water deficit conditions. Drought tolerance indicators (mean productivity, geometric mean productivity, tolerance index and stress tolerance index) were most effective in identifying Urochloa ecotypes with high biomass production under both water deficient and WS conditions. Ecotypes K17, K7, Kisii, Busia and Kakamega were the most drought tolerant, Basilisk, K6, K10, K19 and Toledo were moderately tolerant whereas, CIAT6385, CIAT16449, K13, K5 and K9 were drought sensitive. The five drought-tolerant Urochloa ecotypes should be tested for sustainable biomass production under field conditions and used in breeding programmes to develop high-yielding drought-tolerant varieties.