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Background Drought is a major limiting factor seriously influencing worldwide soybean production and its impact on yield, morphological and physiological traits depend on the timing it occurs and the intensity of water shortage. Only limited research has however been conducted on identifying the drought-tolerant genotypes at different growth stages (vegetative growth phase, reproductive growth phase and the whole growth phase) as well as evaluate the effectiveness and reliability of multiple phenotypic and yield-related characteristics in soybean. Results Two pot experiments and a 2-year field experiment were conducted to evaluate soybean drought tolerance at different growth stages. The membership function value of drought tolerance (MFVD) was used to identify drought-resistant cultivars during vegetative growth phase and reproductive growth stage; the relative drought index (RDI) of yield was used to assess drought-resistant cultivars during the whole growing period. In this study, regression models built based on MFVD indicated that the variation of drought tolerant coefficient (DC) of R/S, TRL, LAI and RSR could explain 73.70% of the total variation at vegetative growth phase. However, higher heritability only found in LAI and RSR, indicating the two traits could serve as reliable criteria for drought evaluation. Similarly, the DC of SPP, YPP, PH, PB, MSNN and STB could explain 94.30% of the total variation in MFVD according to stepwise multiple linear regression analyses at reproductive growth phase. Thus, these six traits were identified as indicators for screening drought resistance genotypes in soybean. In addition, correlation analysis revealed that the MFVD was significantly positively correlated with the DC RB , DC R/S , DC RSA , DC RSR and DC RBR at vegetative growth phase and DC YPP , DC SPP , DC RB, and DC PB at reproductive growth phase. This indicated that these traits were closely related to the drought resistance of plants. Conclusions LD24, JD36 and TF31 of vegetative growth phase, and TD37 and LD26 of reproductive growth phase were identified with drought tolerant and highly drought tolerant, respectively. Moreover, 30 accessions with drought tolerance were screened in the field trial and could be applied for the drought resistance of other genotypes by cross-breeding.

Drought is one of the main abiotic stresses that seriously influences cotton production. Many indicators can be used to evaluate cotton drought tolerance, but the key indicators remain to be determined. The objective of this study was to identify effective cotton drought tolerance indicators from 19 indices, including morphology, photosynthesis, physiology, and yield-related indices, and to evaluate the yield potential of 104 cotton varieties under both normal and drought-stress field conditions. Combined with principal component analysis (PCA) and a regression analysis method, the results showed that the top five PCs among the 19, with eigenvalues > 1, contributed 65.52, 63.59, and 65.90% of the total variability during 2016 to 2018, respectively, which included plant height (PH), effective fruit branch number (EFBN), single boll weight (SBW), transpiration rate (Tr) and chlorophyll (Chl). Therefore, the indicator dimension decreased from 19 to 5. A comparison of the 19 indicators with the 5 identified indicators through PCA and a combined regression analysis found that the results of the final cluster of drought tolerance on 104 cotton varieties were basically consistent. The results indicated that these five traits could be used in combination to screen cotton varieties or lines for drought tolerance in cotton breeding programs, and Zhong R2016 and Xin lu zao 45 exhibited high drought tolerance and can be selected as superior parents for good yield performance under drought stress.

Main conclusionsA novel image-based screening method for precisely identifying genotypic variations in rapeseed RSA under waterlogging stress was developed. Five key root traits were confirmed as good indicators of waterlogging and might be employed in breeding, particularly when using the MFVW approach.Waterlogging is a vital environmental factor that has detrimental effects on the growth and development of rapeseed (Brassica napus L.). Plant roots suffer from hypoxia under waterlogging, which ultimately confers yield penalty. Therefore, it is crucially important to understand the genetic variation of root system architecture (RSA) in response to waterlogging stress to guide the selection of new tolerant cultivars with favorable roots. This research was conducted to investigate RSA traits using image-based screening techniques to better understand how RSA changes over time during waterlogging at the seedling stage. First, we performed a t-test by comparing the relative root trait value between four tolerant and four sensitive accessions. The most important root characteristics associated with waterlogging tolerance at 12 h are total root length (TRL), total root surface area (TRSA), total root volume (TRV), total number of tips (TNT), and total number of forks (TNF). The root structures of 448 rapeseed accessions with or without waterlogging showed notable genetic diversity, and all traits were generally restrained under waterlogging conditions, except for the total root average diameter. Additionally, according to the evaluation and integration analysis of 448 accessions, we identified that five traits, TRL, TRSA, TRV, TNT, and TNF, were the most reliable traits for screening waterlogging-tolerant accessions. Using analysis of the membership function value (MFVW) and D-value of the five selected traits, 25 extremely waterlogging-tolerant materials were screened out. Waterlogging significantly reduced RSA, inhibiting root growth compared to the control. Additionally, waterlogging increased lipid peroxidation, accompanied by a decrease in the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). This study effectively improves our understanding of the response of RSA to waterlogging. The image-based screening method developed in this study provides a new scientific guidance for quickly examining the basic RSA changes and precisely predicting waterlogging-tolerant rapeseed germplasms, thus expanding the genetic diversity of waterlogging-tolerant rapeseed germplasm available for breeding.

Waterlogging (WL) is an important abiotic stress, severely affecting plant growth and development, inhibiting root respiration and degradation of chlorophyll, senescence of leaves and chlorosis leading to substantial yield loss. These intensities of yield losses generally depend on the duration of WL and crop growth stages. Maize being a dry land crop is particularly sensitive to WL. Systematic screening techniques to identify parameters linked with tolerance are not well established which serves as a major bottleneck in the identification of promising genotypes. In this study, 120 maize inbred lines belonging to diverse genetic backgrounds were evaluated for WL tolerance both at pre-emergence as well as the seedling stage. Results based on percentage germination at pre-emergence and percentage survival at the seedling stage under WL established that pre-germination tolerance is independent of seedling stage tolerance. Membership function value based on WL tolerance coefficient of shoot and root fresh weights, dry weights, lengths, root surface area, shoot area and root volume was used to identify tolerant lines. Established mathematical models were used and identified root dry weight as a single reliable parameter to judge the tolerance level of genotypes. The use of BLPSI and ESIM selection indices as well as MTSI to judge the stability as well as genetic worth of genotypes further strengthens the selection efficiency. Lines thus performing best across all the models included I 185, I 172 and SE 503 and were identified as tolerant lines for WL. A combination of these different selection approaches would further strengthen selection efficiency and is believed to be a rapid and effective selection approach.

Salinity tolerance in blackgram is genotype- and growth stage–specific, and the crop is highly susceptible to salinity stress. Therefore, deciphering the tolerance mechanisms of available germplasm is crucial for breeding genotypes with multiple salinity tolerance traits. In this study, a fuzzy logic based comprehensive approach using membership function values (MFVs) was employed to integrate multiple traits involving morphology (root and shoot length and their fresh and dry weights), ion accumulation (sodium and potassium), physiology (SPAD, NDVI, chlorophyll fluorescence, electrolyte leakage, and relative water content), and biochemical parameters (superoxide dismutase, catalase, ascorbate peroxidase, malondialdehyde, chlorophyll, and proline) into a single comprehensive metric for evaluating salt tolerance and to identify promising genotypes. Salinity stress significantly reduced fresh and dry biomass, photosynthetic pigments and related traits, relative water content, and potassium levels, while increasing sodium accumulation, electrolyte leakage, antioxidant enzyme activity, and proline content. Salinity-sensitive genotypes exhibited increased root length and higher sodium ion accumulation across all plant parts. In contrast, tolerant genotypes showed greater photosynthetic efficiency, chlorophyll content, enzymatic activity, higher leaf biomass, and better ion homeostasis throughout the plant. On the basis of principal component analysis (PCA) and membership function values, tolerant (VBG 19010 and VBG 17007) and susceptible (VBG 13003 and ADT 3) genotypes were identified for further molecular dissection. These tolerant genotypes can be used to identify the possible genomic regions and metabolites responsible for salinity tolerance in black gram and serve as valuable resources for crop breeding programs.

Waterlogging stress is one of the major abiotic stresses that negatively affect chrysanthemum (Chrysanthemum morifolium Ramat.) growth and development, thus reducing its productivity. Therefore, there is a need to develop waterlogging-tolerant chrysanthemum germplasms to deal with this problem, and the identification of tolerant wild chrysanthemum (C. indicum) is relevant to the improvement of cultivated chrysanthemum targeting resistance traits. In the current study, we aimed to evaluate the waterlogging tolerance of wild chrysanthemums by using the membership function value of waterlogging (MFVW) and multiple regression analysis based on seven morphological traits related to waterlogging tolerance. By MFVW, the investigated 19 C. indicum accessions were classified into five grades: one waterlogging-tolerant accession, 12 moderately waterlogging-tolerant accessions, and every two accessions for highly waterlogging-tolerant, waterlogging-sensitive, and highly waterlogging-sensitive types, respectively. Of all traits tested, Score, shoot fresh weight, and root fresh weight are considered reliable indicators, exhibiting a higher correlation with waterlogging tolerance. The mathematical evaluation model of waterlogging tolerance based on MFVW proved robust by comparing the observed MFVW and predicted Y values in two interspecific segregating F1 populations derived from C. indicum and C. japonense, with average R2 ranging between 0.957 and 0.982. The method established in the current study provides a reference for the rapid identification and accurate prediction of waterlogging tolerance in chrysanthemum germplasms, and the highly waterlogging-tolerant wild chrysanthemum germplasms identified herein help widen the genetic base for breeding chrysanthemum cultivars with desirable waterlogging tolerance.

Finger millet is a drought-tolerant crop that grows better under water-limited conditions. However, a lack of moisture during germination affects seedling emergence and growth, ultimately affecting crop yield. Hence, identifying germplasm accessions that are drought tolerant could be of great importance to breeders. However, no systemic approach has been proposed for screening finger millet germplasm accession for moisture stress at the seedling stage. In the present study, we evaluated drought tolerance using PEG-8000 mediated moisture stress in 92 finger millet germplasm. The membership function value (MFV) was used as an index to assess and select finger millet germplasm for drought tolerance. Furthermore, a regression model was designed based on the mean MFV of all traits, which explained more than 95% of the variation in the total population. Of all the examined traits, the seedling vigour index was the most reliable, showing the highest correlation with drought tolerance at the seedling stage. We also developed an effective mathematical evaluation model for assessing finger millet germplasm for drought tolerance at the seedling stage. These findings laid the groundwork for further research into drought-tolerance mechanisms and the development of drought-tolerant finger millet cultivars. Highlights Screening large germplasm under field conditions for drought tolerance could be laborious, costly and time consuming; therefore, screening at laboratory level could be easy, cost-effective, and require less time. Screening using several models like percent reduction, stress tolerance index, etc. could be considered, but the membership function value (MFV) could be a better approach, which considers all the parameters and all the genotypes in calculating the MFV value. Using the MFV values, all the released cultivars were found moderately tolerant, and a few stress-tolerant accessions, were GE-50, GE-4568, GE-128, GE-1026, and GE-6998. The highly susceptible accessions were GE-837, GE-1309, GE-4976, and GE-5123.

Soil salinization, recognized globally as a significant environmental issue, can directly impact the sustainable development of agriculture worldwide. As a key crop driving the global agricultural economy, maize is particularly vulnerable to the detrimental effects of salt–alkali stress, which can impede its growth and development from germination through the seedling stages. In this study, 32 maize inbred lines were screened for saline–alkali resistance identification. We performed four treatments—200 mmol/L NaCl, 100 mmol/L Na2CO3, 200 mmol/L NaCl with 25 mmol/L Na2CO3—and distilled water (CK) served as a control with a complete randomized design. Principal component analysis and the membership function value method were employed to evaluate the salt–alkali tolerance of these lines. The results indicate complex correlations among various traits at different growth stages. The relative correlation of each index was established by measuring the key physiological indexes (germination rate, root length and seedling height) of different maize inbred lines at the germination stage and seedling stage and standardizing them via the membership function value method. Subsequently, the principal component analysis method was used to reduce the dimensions of the standardized data, and the main factors affecting maize germination and seedling growth were extracted. The salt–alkali tolerance of maize inbred lines was comprehensively evaluated, and the salt–alkali tolerance and sensitive materials of maize germination and seedling stage were identified. This study found that the coefficient of variation of each trait is relatively rich. Therefore, in the preliminary screening of breeding germplasm resources, different reference indexes can be selected according to different periods and stress conditions. The enzyme activity results revealed significant variations in enzyme activity across different treatments and materials, with changes in superoxide dismutase (SOD) and peroxidase (POD) exhibiting relative stability, thereby reflecting the physiological response mechanisms of maize under salt–alkali stress. In this study, through principal component analysis, it was found that the germ and germination factors at the germination stage of maize and the root weight, root length, and seedling development factors at the seedling stage affected its saline–alkali resistance. The root weight factor, seedling development factor, and root length factor may affect the growth and development of maize at the seedling stage. Through the comprehensive analysis of the data of the germination stage and seedling stage, it can be seen that the materials with better salt resistance are Zm4 and Zm32; the material with better alkali resistance is Zm30; the material with better salt and alkali resistance is Zm2. Through the application of comprehensive evaluation system, researchers can more effectively screen out maize germplasm resources with excellent genetic characteristics to promote maize variety improvement and genetic diversity protection.

Expanding the cultivation of pearl millet into salt-affected soils necessitates the development of genotypes with enhanced sodicity tolerance. Evaluating the tolerance levels of existing cultivars is a crucial first step in this direction. Thus, in this study, we assessed the performance of 23 genetically diverse pearl millet hybrids through a semi-controlled pot experiment under control (pH ~ 7.5) and sodic (pH ~ 9.2) conditions during the seedling-to-vegetative stage. A comprehensive assessment of 14 morphological and physiological traits revealed significant genotype, treatment, and genotype × treatment interactions, highlighting the varied responses of hybrids to sodic stress. Among the measured parameters, root biomass showed the most significant reduction (65.88%) under sodicity, while relative water content was the least affected (12.2%). Sodium accumulation in both the shoot and root negatively correlated with all morphological traits, emphasizing its harmful impact on growth. Based on ion homeostasis and growth performance, hybrids JKBH 1326 and RHB 234 displayed superior ion exclusion mechanisms, whereas BHB 1602 and HHB 67 IPM exhibited tissue tolerance. Membership function values derived from stress tolerance indices identified HHB 67 IPM, MPMH 17, RHB 234, and GHB 1129 as the most promising genotypes under sodic stress. Furthermore, random forest modeling and SHAP (SHapley Additive exPlanations) analysis indicated that soil nitrogen, and potassium were the primary determinants of shoot and root biomass in sodicity. These findings offer essential insights into the morphological and physiological responses of pearl millet to sodicity and pinpoint promising hybrids for potential cultivation in degraded soils, warranting further validation under field conditions.

Salinity stress is one of the most important abiotic stresses which reduce crop production worldwide. In this study, 17 morphological and agronomic traits as indicators for identifying salinity tolerance genotypes in wheat were evaluated among a set of 110 different genotypes including advanced lines in breeding programs, and wheat landraces collected from landraces throughout Iran, some well-known tolerant and sensitive cultivars and many commercial wheat cultivars. Plant materials were grown under non-saline (NS) and saline stress (SS) conditions (Electrical conductivity [EC] of 2 and 10 ds m−1, respectively). The membership function value of salinity tolerance (MFVS) was used as a comprehensive index for the evaluation and selection of wheat salinity tolerance. The mean value of all 17 traits decreased under saline stress conditions. Among the 17 traits, spike weight (SW), kernel weight per spike (KWS), number of fertile tillers (NFT), biological yield (BY), and grain yield (GY) decreased > 25%. This suggested that these 5 traits were more sensitive to salinity stress. Ten genotypes with high salinity tolerance were selected based on MFVS and could be applied for salinity tolerance improvement in wheat. Correlation analysis indicated that the wheat salinity tolerance was significantly and positively correlated with variations of 13 traits under both non-saline and saline stress conditions (P < 0.01). Factor analysis showed that salinity-tolerant coefficients of 5 traits of grain yield, biological yield, spike weight, kernel weight per spike, and number of fertile tillers have the most interrelationships with the membership value of salinity tolerance (MFVS). Therefore, these five traits could be applied as an indicator to screen wheat germplasm for salinity tolerance in wheat breeding programs.