High Stress Tolerance Index Research Articles

Genetic variability for salinity tolerance of tomato (Solanum lycopersicon MILL.) genotypes determined by stress tolerance indices

BackgroundTomato is an important vegetable crop; however, salinity hampers its growth and yield-related traits. Different tomato genotypes significantly differ in their salinity tolerance; thus, selecting the tolerant genotypes could improve yield and productivity under saline environments. MethodsThis study investigated salinity tolerance of five tomato genotypes, i.e., ‘Pakit’, ‘Riogrande’, ‘Roma’, ‘Continental’, and ‘Nagina’ under 0-, 100-, 150- and 200-mM salinity levels. Data relating yield-related traits (plant height, shoot fresh and dry weights, number of fruits per plant, single fruit weight and fruit yield per plant) and nine different stress tolerance indices were employed to infer salinity-tolerance of the genotypes. ResultsIncreasing salinity levels negatively affected the yield-related traits of genotypes; however, genotypes exhibited varied tolerance to salinity. The better and the poor yield-related traits were noted under 0- and 200-mM salinity levels, respectively. Similarly, genotypes ‘Pakit’ and ‘Nagina’ recorded the highest and the lowest values of yield-related traits. The genotype ‘Pakit’ proved the most tolerant to tested salinity levels compared to the rest of the genotypes. The ‘Pakit’ genotypes had the highest stress tolerance index (0.19, 1.06 and 1.79) and the lowest relative change in yield (6.00, 32.59, and 55.75%) under all salinity levels. Principal component analysis biplot revealed that ‘Pakit’ genotypes had superior yield traits and tolerance indices. ConclusionThe genotype ‘Pakit’ exhibited a higher level of salinity tolerance (6 % yield reduction under 100 mM salinity compared to 27.67 % reduction in ‘Nagina’ genotype. Therefore, genotype ‘Pakit’ can be recommended for cultivation on low to moderate saline soils without significant yield losses. On the other hand, ‘Nagina’ genotype proved the most sensitive to salinity (27.67 %, 56.79 %, and 68.90 % yield reduction under 100-, 150-, and 200-mM salinity, respectively). Therefore, this genotype should not be cultivated on saline soils.

The 5-azacytidine-induced epimutagenesis of sugarcane (Saccharum spp. hybrids) for aluminium tolerance

A protocol for generating aluminium (Al) tolerant sugarcane using 5-azacytidine (5-azaC)-induced epimutagenesis was developed. Eight (8) plantlets per gram of cultivar N51 calli were generated from the 5-azaC (100 μM) and Al (1.5–50 mM) treatment (+Az + Al) when compared with 104 plantlets from non-mutagenised, no Al control treatment. Following in vitro selection on 60 mM Al, ex vitro stress over four rounds of chimera dissolution during vegetative propagation was applied. In the final stress round, 36% of the Mut 2 epilines survived with plants showing higher relative water content (61.2%) when compared with 47.3% from the stressed control (S N51). The Mut 2 line maintained a higher green leaf area (83.4%) and longer roots (32.4 cm) under stress than S N51 (61.4% and 26.3 cm, respectively). Overall, Mut 2 had a high stress tolerance index of 85.4%, compared with 79.0% from the S N51, nearing that of the non-stressed N51 control (NS N51, 100%) when data were analysed using PCA and clustering analyses of morpho-physiological traits. Analysis of molecular variance (AMOVA) revealed high epigenetic differentiation (ɸst = 0.67) and a variation of 66.6% observed among N51 genotypes. The principal coordinate analysis (PCoA) showed that Mut 2 was epigenetically distinct from S N51. These findings support previous studies that 5-azaC can be used for novel trait creation via epimutagenesis and highlights the necessity for chimera dissolution to achieve stable traits in epibreeding of sugarcane.

Field identification of drought tolerant wheat genotypes using canopy vegetation indices instead of plant physiological and biochemical traits

Seasonal drought is a major limiting factor for wheat production in the North China Plain. The use of non-destructive screening tools based on vegetation indices associated with physiological and biochemical traits will help in the identification of drought-tolerant wheat genotypes to counter drought stress. The objectives of this study were to characterize the performance of 10 wheat genotypes with different genetic backgrounds in terms of physical and biochemical traits under two contrasting moisture regimes, and to evaluate the effectiveness of vegetation indices/spectral measurement techniques for assessing drought tolerance in wheat. Traits associated with drought stress were assessed in the 10 wheat genotypes, including plant biophysical parameters, drought tolerance parameters, as well as various vegetation indices. Significant variability was found wheat genotypes with different genetic backgrounds to water stress. The clustering results indicated that Luohan-19, Luohan-22, and Jinmai-47 were drought-tolerant genotypes characterized by high stress tolerance index (STI) values (0.548, 0.535 and 0.523, respectively), drought index (DI) values (0.517, 0.524 and 0.504, respectively), and drought tolerance coefficient (DC) values (1.065, 1.074 and 1.000, respectively). Based on principal component analysis and membership function, genotypes were classified as tolerant (Luohan-19, Luohan-22, and Jinmai-47), moderately tolerant (Luomai-26, Zhongmai-175, and Bainong-207) and sensitive (Yunong-516, Zhongmai-895, Annong-0711 and Huacheng-3366) to water stress, with comprehensive evaluation values (D) of >0.761, 0.422–0.761, and <0.422, respectively. Heatmap analysis of various vegetation indices for screening wheat genotypes showed similar results to the multivariate data analysis; that is, genotypes Luohan-19, Luohan-22, and Jinmai-47 were identified as drought-tolerant genotypes. Among these vegetation indices, the normalized difference water index (NDWI) and the red edge chlorophyll index (CIred edge) were highly correlated with the drought tolerance indices, such as STI and DI (r2 >0.717), and are therefore recommended as rapid indicators for the identification of tolerance genotypes in the field. These vegetation indices, particularly NDWI and CIred edge, exhibited similar performance to the drought tolerance indices and multivariate data analysis results in identifying drought-tolerant genotypes, and thus they can be used as alternative and inexpensive measures for identifying drought tolerance in wheat in the future.

Traits associated with higher productivity and resilience to drought-prone Mediterranean environments of coastal-lowland quinoa (Chenopodium quinoa Willd.)

Quinoa (Chenopodium quinoa Willd.) is an Andean crop that has been cultivated for over 7000 years in Andean South America. Among the five quinoa ecotypes identified, the coastal-lowland ecotype is distributed in central-southern Chile. Little is known about the phenotypic variability of this germplasm and its productive potential. In this work, we evaluated a panel of 99 self-pollinating genotypes of quinoa under rainfed and irrigated conditions in the Mediterranean area of central Chile. The aim was i) to evaluate the phenotypic variability of agronomic and leaf photosynthetic traits; ii) to assess trait responses to environmental conditions (rainfed and irrigated) and their heritability; and iii) to identify traits and genotypes associated with high yield potential and resilience in drought-prone environments. The selected genotypes were evaluated under rainfed (Hidango; 34° 06' S, 71°47' W) and irrigated (Santa Rosa; 36°31' S, 71°54' W) conditions, in two growing seasons (2016/17 and 2017/18). In the most favorable environment (Santa Rosa 2016), the shoot dry weight (shoot DW) and grain yield (GY) of the different genotypes, ranged from 655 and 2787 g m-2 (average 1440 g m-2) and from 45 and 452 g m-2 (average 244 g m-2), respectively. Under rainfed conditions (at Hidango), the shoot DW and GY were reduced by 75 % and 74 %, respectively, compared to Santa Rosa 2016, but still, some genotypes produced more than 100 g m-2, with < 70 mm of precipitation, evidencing a high drought tolerance. The harvest index (HI) and grain weight (TKW) were less affected by drought; compared to Santa Rosa 2016, the reduction was 8–18 % and 25–29 %, respectively, in 2016/17 and 2017/18. Days from sowing to flowering (DSF) and from flowering to maturity (DFM) varied among genotypes and were negatively correlated with GY and HI. Under rainfed conditions, the fluorescence parameters F0 and Fm were reduced by 30 % during flowering and by 50 % during grain-filling, compared to irrigated conditions. The HI and TKW showed the highest heritability (0.69) and were highly correlated with GY in all environments. This study showed that traits associated with higher productivity and resilience of quinoa genotypes in rainfed Mediterranean environments were early maturating and with high HI, and TKW. Finally, a set of genotypes presenting a high stress tolerance index (STI), and therefore higher tolerance to drought conditions, were identified and are candidates for further research focused on the selection of parentals for more advanced breeding stages.

Yield-based drought tolerance index evaluates the drought tolerance of cotton germplasm lines in the interaction of genotype-by-environment.

Cotton is an economically important crop in China, and drought has seriously affected cotton production. Understanding genetic variation, genotype ×environment interactions, and the associations between these traits is critical for developing improved cotton varieties with high drought tolerance. To screen ideal drought-resistant cotton germplasm lines and excellent genotypes, the yield traits of 103 cotton germplasm lines were analyzed. Cotton resource material was planted under normal watering and water deficit conditions for three consecutive years. The yield traits under normal irrigation and water stress conditions were measured, and then five screening indicators were calculated based on the cotton yield per plant under the two water treatments to determine the ideal genotype and most accurate identification indicators. The results of correlation analysis and principal component analysis showed that the geometric mean productivity (GMP), mean productivity (MP), and stress tolerance index (STI) were significantly positively correlated with yield under water stress and could be used to distinguish genotypes with high drought tolerance. Among the experimental germplasm lines, some had higher STI and GMP values, indicating their higher drought tolerance. This result indicates that best linear unbiased prediction (BLUP) analysis of the STI and GMP under drought stress can effectively improve screening for drought tolerance in cotton germplasm lines. The results from the screening index, three-dimensional map, and genotype ×environment (GGE) biplots were consistent with the above results. We determined that CQJ-5, Xin lu zao 45, Bellsno, Zhong R 2016 and ND 359-5 are drought-tolerant genotypes that can be used to breed drought-tolerant germplasm lines that produce high and stable yields.

Response of Rice Genotypes to Boron Fertilization and Screening of Efficient Rice Varieties under Boron Stress in Inceptisol

A pot culture experiment was conducted on Karaikal soil series (Vertic Ustropept) to study the response of rice genotypes to boron addition and screening efficient genotypes using stress indices. Ten rice genotypes were tested at two (0, 2 mg kg-1) level of boron. The result revealed that the highest grain yield (88.40 g pot-1) and straw yield (114.7 g pot-1), and the maximum grain boron uptake (2192.3 µg pot-1) and straw boron uptake (3291.9 µg pot-1) were recorded with application 2.0 mg boron kg-1. Amongst rice genotypes, ADT 50 recorded significantly the highest grain and straw yield, boron uptake and boron use efficiency compared to other genotypes on application of boron @ 2 mg kg-1. From the study results, we observed that there are significant differences among rice genotypes on yield, boron uptake and use efficiency with boron fertilization compared to no boron application. Further, based on stress tolerance index (STI), yield under stress (Ys) and adequate condition (Yp) rice genotypes were categorized into Group A – uniform superiority under stress and non – stress condition – ADT 50, ADT43 and ADT 53 with high STI &gt; 1.0; Group B - perform favorably only under non – stress condition - ADT 46, ADT 52,ADT 51, ADT 40 and ADT 37 – STI - 0.7 to 1.0; Group C – genotype yield relatively higher only under stress environment – no genotypes ; Group D – genotype perform poorly in both stress and non-stress environment – ADT 38 and ADT 39 with low STI &lt; 0.70.

Documentation of Parents and Hybrids Tolerant to Terminal Heat Stress in Brassica juncea L.

Background: Fluctuations in temperature during the growth period can damage the inter-molecular interactions needed for proper growth, thus impairing plant development and fruit set, which leads to significant yield loss with greater risks for future global food availability, food accessibility, food utilization and food systems stability. Keeping these in mind present investigation was done to identify of parents and hybrids for terminal heat tolerance. Methods: Nine lines and three testers were crossed in line × tester fashion to develop hybrids. F1s were evaluated under timely and late sown conditions to study the effect of terminal heat stress by calculating, heat susceptibility index (HSI), heat tolerance efficiency (HTE) and stress tolerance index (STI) on yield and yield traits and to characterize parents and crosses on the basis of their relative tolerance against heat stress at the Agriculture Research Farm, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi during Rabi 2017-18 and 2018-19. Result: Observations were made for different yield and yield related traits. Genotypes such as BPR 541-4 was found to be tolerant to heat stress at terminal stage and crosses such as Vardan × PM 30, Kranti × RH 406 and Kranti × Urvashi were found to be tolerant to heat stress for seed yield per plant at terminal stage during 2017-18 and 2018-19. Genotypes and crosses that were found to have minimum reduction in seed yield manifested tolerance to heat stress in terminal stage (had lowest HSI, Highest HTE and Highest STI).

Mungbean germplasms tolerance to salinity stress correlated with age character and potential yield

Mungbean is of the important legume commodity in Indonesia, however the production is still encountering the abiotic salinity stress. Fifty mungbean accessions were evaluated for the salinity tolerance at Indonesian Legumes and Tuber Crops Research Institute (ILETRI). The experimental was arranged in Split Plot Design consisted of two factors and three replications. The main plot was two environments, normal and salinity stress that was applied using diluted seawater, while the subplot was mungbean accessions. The parameters including soil electrical conductivity, time to first flowering and seed maturation, plant height, leaf chlorophyll index, salinity toxicity score, and seed yield per plant were observed. Salinity stress decreased mungbean seed yield with ranged from 61.33 - 100%. The highest stress tolerance index (STI) were found in Vima 4-MLGV 1118 (STI=0.58) and MLGV 1065 (STI=0.53). Five accessions did not able to produce any seed. Mungbean accessions tolerance to salinity stress was negatively correlated with the time of first flowering and seed maturation, while it was positively correlated with potential yield both in normal and salinity stress. It is suggested that selection and evaluation of mungbean to salinity stress in the future should be categorized both by the plant age and potential yield.

Beet Molasses Enhance Salinity Tolerance in Thymus serpyllum—A Study under Greenhouse Condition

The growing demand for Thymus serpyllum biomass to produce drugs, cosmetics and spices necessitates the search for innovative methods mitigating the negative effects of environmental stressors in order to improve its yield under unfavorable conditions. Due to the exposure of plants to salinity stress (SS), we investigated the effect of sugar beet molasses (SBM) on the growth and biochemical parameters related to plants’ response to SS. Wild thyme plants were treated for 5 weeks to sodium chloride and 3% molasses solution using two modes of application (soil irrigation or foliar sprays). Plants irrigated by SBM showed slighter stem growth inhibition than control plants, high stress tolerance index and maintained a constant root water content under salt stress. Moreover plants treated with 100 mM NaCl and soil-applied SBM had lower lipid peroxidation level, showed lower POD activity, higher total soluble protein content and maintained a more even free amino acids level, compared to the control treatments. The concentration of potassium ions was higher in the case of plant roots irrigation with sugar beet molasses compared to control plants. In this experiment, most of the growth and biochemical parameters from foliar molasses-sprayed plants did not differ significantly from the control. We provided evidence that soil-applied SBM beneficially changed the plant’s biochemical response to salt stress. On the basis of the obtained results, we conclude that this soil amendment contributes to the strengthening of plant protection against this harmful environmental factor.

Biomass yield, dry matter partitioning and physiology of commercial and Erianthus introgressed sugarcane clones under contrasting water regimes

The productivity of sugarcane is limited by several biotic and abiotic stresses, of which drought is an important environmental stress, causing substantial yield losses especially in tropical parts of the world. The present day sugarcane cultivars are derivatives of interspecific hybrids involving Saccharum officinarum and S. spontaneum and the drought tolerance is governed by S. sponaneum. Of late considerable attention has been given to utilize Erianthus Spp, the related wild genera of Saccharum, shows remarkable levels of drought tolerance under water limited condition. In this study, experiments were conducted to compare the influence of drought on biomass, yield and physiology of commercial and Erianthus introgressed clones. The results showed that the cane yield was reduced 37.98% in commercial clones compared to 24.67% in Erianthus introgressed clones under drought. The highest stress tolerance index (STI) of 1.256 was recorded in the clone CYM 08–922 which is a backcross hybrid involving Erianthus arundinaceus. Significant differences were observed for leaf area index, relative water content, lipid peroxidation and epicuticular wax content among the genotypes and between treatments. Sugar yield was most affected by drought (38.86%) followed by cane yield (33.30%), NMC (26.79%) and single cane weight (22.49%). Cane yield showed a positive and significant correlation with dry biomass under both irrigated (r = 0.303) and drought situations (r = 0.404) and among the physiological parameters, only RWC showed significant and positive correlation with cane yield (r = 0.307). The leaf dry matter was 14.55% higher under drought indicating influence of drought on translocation of dry matter from leaves to canes. Among clones CoM 0265, Co 06022, CYM 08-922, CYM 09-1369 and GU 12-31 showed greater ability to partition dry matter in to canes under drought than the other clones and had higher stress tolerant index. Cane height, number of millable stalks and RWC% showed positive and significant association with cane yield under both drought and irrigated condition and could be important parameters in screening clones under sugarcane improvement programmes.

Water-stress Screening in Blackgram [Vigna mungo (L.) Hepper] Genotypes using Polyethylene Glycol 6000 at Seedling Growth Stage

Background: Blackgram is one of the important pulse crops belongs to the Papilionaceae family. Seed germination and seedling growth are a very important step in the survival of a plant. Water stress is one of the important factors affects seedling growth. Methods: An experiment was conducted to study the effect of water stress on seedling growth in twenty-one blackgram [Vigna mungo (L.) Hepper] genotypes at the pot culture yard of Annamalai University during March 2018. The water stress was created by using Polyethylene Glycol (6000 MW) in different concentrations (0%, 10% and 20%). Different phenotypic characters were recorded such as shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight at two different levels of treatment and control. The experiment was laid in a completely randomized design with two replications. Result: The combined analysis of variance revealed significant differences (p less than 0.001) among genotypes, treatments and genotypes × treatments interaction. The highest stress tolerance index (STI) was recorded by the genotype ADT-5. Based on clustering and ranking, the genotypes ADT-5, KGB-28, RU-16-9, VBG-10010 and VBG-12062 were classified as drought-tolerant. Overall, pot culture screening of 21 blackgram genotypes for drought tolerance at seedling stage using various concentrations of PEG 6000 resulted in the identification of drought-tolerant genotypes, where ADT-5 showed the highest tolerance followed by KGB-28 and RU-16-9.

Selection of drought tolerant genotypes in groundnut (Arachis hypogaea L.) using indices

A study was carried out to evaluate the effect of drought stress on pod yield and other traits of groundnut genotypes to select the ten best performing genotypes using indices. Ninety six genotypes including 90 F2:3 progenies, 4 parents and 2 checks were planted under well-watered (WW) and water-stressed (WS) conditions at the International Crops Research Institute for the Semi-Arid Tropics ICRISAT, Mali. Six selection indices including mean productivity (MP), tolerance (TOL), geometric mean productivity (GMP), stress tolerance index (STI), drought tolerance index (DTI) and reduction (%) (RED) were used. The indices were adjusted based on pod yield under WW and WS conditions. High DTI, STI, MP, and GMP values under both well-watered and water-stressed conditions were more effective in identifying high yielding cultivars under water limited conditions. Based on these indices, the F2:3 progenies ICGV-IS 13012F2-B1-297, ICGV-IS 13012F2-B1-40, ICGV-IS 13005F2-B1-46, ICGV-IS 13005F2-B1-252, ICGV-IS 13012F2-B1-29, ICGV-IS 13005F2-B1-205, ICGV-IS 13005F2-B1-287, ICGV-IS 13012F2-B1-525, ICGV-IS 13012F2-B1-576 and ICGV-IS 13005F2-B1-91 were identified as the most drought tolerant genotypes with high yield stability in the well-watered and drought stress conditions. The indices STI, MP and GMP were positively correlated with pod yield under WW and WS conditions and breeding for drought tolerance. Key words: Groundnut, breeding, selection indices, drought stress.

Respons Genotipe Kedelai sebagai Tanaman Sela pada Tumpang Sari dengan Ubi Kayu

Soybean development to intercropping is one of the opportunities to increase soybean planting area. Each soybean variety has different responses to intercropping so it is required to study soybean varieties that are suitable or adaptive to intercropping environments. Therefore, a research was conducted to determine the response of soybean genotypes in intercropping with cassava. The research was conducted at the Jambegede Research Station, Malang in February to December 2018, in two environments, namely intercropping (L1) and monoculture (L2), with two planting times, namely three weeks (T1) and 4 months (T2) after cassava planting. Twelve promising lines and three varieties (Dena 1, Dena 2, and Grobogan) were used as research materials. A completely randomized block design with three replications was used to arrange the treatments in each environment. The results showed that the responses of each soybean genotype tested as intercrops on intercropping system with cassava were varied, depending on the soybean planting time. GH-5 and GH-6 soybean genotypes are suitable for the first intercrop (T1), while GH-3 are suitable as the second intercrops (T2) in intercropping system with cassava + Soybean, with higher stress tolerance index (STI) and lower weighted sensitivity index (WSI) than the other genotypes tested. Based on the land equivalent ratio (LER), intercropping of cassava with GH-5, GH-6, or GH-3 soybean genotypes was advantageous (RKL&gt;1.0). Keywords: land equivalent ratio, stress tolerance index, weighted sensitivity index

Effectiveness of physiological traits in adopting safflower (Carthamus tinctorius L.) genotypes to water deficit condition

Water deficit is the most limiting factor for seed yield of crop species in the arid and semi-arid regions. Due to increasing limitation of fresh water resources and importance of safflower (Carthamus tinctorius L.) as a significant oilseed crop in Iran, it is necessary to evaluate physiological responses of drought tolerance and its association with seed yield of this crop in water stress condition. In this study, 21 safflower genotypes were planted by hand in the field under water stress and non-stress conditions in a randomized complete block design with two replications during 2 years (2016–17). The results indicated that water deficit stress significantly reduced relative water content (RWC), chlorophyll a (Chl-a) and chlorophyll b (Chl-b) concentrations and seed yield, but increased ascorbate peroxidase (APX) and peroxidase (POX) activities and leaf proline concentration. Significant differences were observed among the genotypes for all studied traits except Chl-b concentration. Genotypes were discriminated according to their response to drought using stress tolerance index (STI). Drought tolerant genotypes displayed a higher capability for accumulation of proline in association with maintaining RWC, antioxidant enzymes activity and higher seed yield, compared to the drought sensitive genotypes. Presented results suggested that safflower genotypes with higher levels of antioxidant enzymes activity, RWC and proline accumulation are characterized by a higher STI. Therefore, these physiological traits can be employed as effective criteria for selecting safflower genotypes with more tolerance to water deficit stress.

Water use Efficient Sunflower Hybrids having Diverse Cytoplasmic Background

Abstract A set of fifty two hybrids developed through line×tester breeding design were sown in randomized block design with three replications to evaluate their performance for seed yield under two environments (normal irrigation and water stress). Drought resistant indices and multivariate statistical analysis from the pooled data obtained from water stress and normal irrigated environments over the two years. Hybrid PRUN-29A × RCR-8297 (1.55) and 40A × P100R (1.55) had the largest stress tolerance index (STI) rate and hybrid ARG-2A × P69R the smallest rate (a high STI rate for the genotype represents its high drought resistance and its high yielding potential). Hybrid ARG-6A × P69R (2.41) had the largest extent (susceptible) of Stress susceptibility index (SSI), while hybrid E002-91 × RCR-8297 (0.13) had the least (resistant) extent a large extent of this index indicates the genotype susceptibility to drought. In terms of yield stability index (YSI), hybrid 40A × RCR-8297 (0.51) and ARG-6A × P69R (0.51) and hybrid ARG-2A × P69R (1.18) had the smallest and the largest rate respectively (genotypes with high YSI are expected to yield highly in stress conditions. Hybrid 40A × RCR-8297 (30.36) and PRUN-29A × P69R (−10.07) displayed the least and the most amount of tolerance index (TOL) index, a high amount of TOL is a sign of genotype susceptibility to stress. Hybrid PRUN-29A × P69R (1.53) displayed the least extent of yield index (YI), while hybrid ARG-6A × P69R (0.51) and 40A × RCR-8297 (0.51) displayed the highest extent.

Arbuscular Mycorrhizal Fungus Improves Rhizobium–Glycyrrhiza Seedling Symbiosis under Drought Stress

Rhizobia and arbuscular mycorrhizal (AM) fungi can potentially alleviate the abiotic stress on the legume Glycyrrhiza (licorice), while the potential benefits these symbiotic microbes offer to their host plant are strongly influenced by environmental factors. A greenhouse pot experiment was conducted to investigate the effects of single and combined inoculation with a rhizobium Mesorhizobium tianshanense Chen and an AM fungus Rhizophagus irregularis Walker &amp; Schuessler on Glycyrrhiza uralensis Fisch. seedling performance under different water regimes. Drought stress inhibited rhizobium nodulation but increased mycorrhizal colonization. Furthermore, co-inoculation of rhizobium and AM fungus favored nodulation under both well-watered and drought stress conditions. Glycyrrhiza seedling growth showed a high mycorrhizal dependency. The seedlings showed a negative growth dependency to rhizobium under well-watered conditions but showed a positive response under drought stress. R. irregularis-inoculated plants showed a much higher stress tolerance index (STI) value than M. tianshanense-inoculated plants. STI value was more pronounced when plants were co-inoculated with R. irregularis and M. tianshanense compared with single-inoculated plants. Plant nitrogen concentration and contents were significantly influenced by inoculation treatments and water regimes. R. irregularis inoculation significantly increased plant shoot and root phosphorus contents. AM fungus inoculation could improve Glycyrrhiza plant–rhizobium symbiosis under drought stress, thereby suggesting that tripartite symbiotic relationships were more effective for promoting plant growth and enhancing drought tolerance.

Physiological aspects of inter-specific gene introgression to improve drought tolerance in safflower

Wild introgression may play an important role to improve drought tolerance of safflower (Carthamus tinctorius L.). Response of populations derived from inter-specific hybridization to drought stress in terms of physiological traits and the possibility of selection of superior lines are poorly understood in safflower. Inter-specific hybridizations were performed to produce three populations of TP (C. tinctorius × C. palaestinus), PO (C. palaestinus × C. oxyacanthus), and TO (C. tinctorius × C. oxyacanthus). In total, a number of 189 lines derived from hybridization along with their parents were evaluated in the field in F3 (2015), F4 (2016) and F5 (2017) generations under normal and drought stress conditions. The results indicated that under drought stress condition, C. tinctorius and C. palaestinus had higher malondialdehyde and proline content, while the highest relative water content was belonged to C. oxyacanthus. Consequently, various inter-specific populations behaved differently to decrease the effect of drought stress. TP and TO with C. tinctorius as their common parent, had higher seed yield and seed yield component than PO population. TP population was the most tolerant population due to its highest stress tolerance index, while TO population showed the highest seed yield stability under deficit irrigation. The results indicated that gene introgression from wild relatives into cultivated safflower gene pool increased genetic variation and provided the chance of selection of superior drought tolerant genotypes for future breeding programs.

Evaluation of rice genotypes for seedling and reproductive stage drought tolerance

The present investigation was undertaken to evaluate 25 drought tolerant genotypes for seedling stage and reproductive stage drought tolerance. The genotypes were evaluated under gravimetric method at three moisture levels viz., i) control at 100% field capacity (FC) ii) water-deficit stress at 80% Field capacity (80% FC) and iii) water-deficit stress at 60% Field capacity (60% FC) for seedling stage drought tolerance. Observations were recorded on six morphological traits viz., seedling height, root length, shoot length, dry weight, leaf rolling and leaf drying and three physiological traits viz., chlorophyll stability index, proline content and nitrate reductase activity. The variety, APO and landraces viz., Kuliyadichan, Kattanur and Sivappuchithiraikar were identified with all desirable drought tolerant seedling traits and these genotypes also had high stress tolerance index (STI) for all the morphological traits. For reproductive stage drought tolerance, the moisture stress was imposed under field condition. Yield characters viz., number of days to maturity, panicle length, spikelet fertility and single plant yield and three physiological traits viz., chlorophyll stability index, proline content and nitrate reductase activity were recorded. Based on stress tolerance index (STI) and high mean performance, varieties viz., Anna (R) 4 and APO and landraces viz., Kattanur, Kuliyadichan and Sivappuchithiraikar were identified as drought tolerant lines for reproductive stage drought tolerance. From this study, APO, Kattanur, Kuliyadichan and Sivappuchithiraikar were identified as drought tolerant lines for seedling stage as well as reproductive stage. Therefore, these genotypes can be used as potential donors in the development of new drought tolerant varieties in rice.

Evaluation of Drought Tolerant Rice Cultivars Using Drought Tolerant Indices under Water Stress and Irrigated Condition

Drought is the most critical abiotic factor reducing rice yield in rainfed and drought prone areas. Majority of rice cultivated area in south Asia are under rainfed, where water stress at any of the critical growth stage causes sharp decline in yield. Research was conducted in western Nepal at farmers field around the close vicinity of Regional Agriculture Research Center (RARS) Nepalgunj. Ten different rice cultivars were evaluated under drought stress and non-stress condition during the year 2017 to identify superior stress tolerant cultivars. Different drought tolerance indices like stress tolerance (TOL), Stress tolerance index (STI), Stress susceptibility index (SSI), were tested in screening superior rice cultivars. Significant reduction in mean grain yield was observed under drought stress in all rice cultivars under the study. The rice cultivars with high STI values and low TOL and SSI were identified as superior drought tolerant cultivars. Based on results of different tolerance indices, Sukha series of rice, Sukha Dhan 1-6 and Radha-4 showed low TOL and SSI and high STI values and were identified as drought tolerant cultivars. The present study reveals that selection based on drought tolerance indices can be an efficient tool in identification of superior drought tolerant cultivars with higher yield and stability.

Genetic variation in an orchardgrass population promises successful direct or indirect selection of superior drought tolerant genotypes

AbstractImprovement in drought tolerance is an important component of forage grass breeding. To assess the potential of selecting drought tolerant genotypes of orchardgrass, a polycross population was created in 2010 and evaluated in the field under normal and drought stress conditions during 2011–2013. Drought stress reduced performance in forage yield, growth characteristics, and most of the physiological traits measured, but increased carotenoid content, proline content, and the chlorophyll a/b ratio. High estimates of narrow‐sense heritability for chlorophyll and carotenoid content, as well as forage yield components, indicated that phenotypic selection would be successful in achieving genetic progress. Indirect selection to improve forage yield under drought stress conditions was efficient through selecting for chlorophyll a, chlorophyll b, total chlorophyll and carotenoid content. These physiological traits were also significantly associated with drought tolerance index. Overall, families 5, 7, 8, 13, 14 and 24 with high stress tolerance index values and high forage yield under both water conditions were identified as suitable families for breeding drought adaptive varieties.