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Rice crop is known to be sensitive to heat stress particularly at the flowering stage. Breeding approaches for improving heat tolerance in rice needs understanding of heat tolerance mechanisms and suitable heat tolerance donors. A study was planned for screening of rice genotypes and identification of novel heat tolerant donor(s) and physiologically characterize the component traits using contrasting set of genotypes in green house environment. Genotypes were categorized as tolerant and sensitive to heat stress using heat susceptibility index and cumulative stress response index for spikelet fertility, pollen viability, and grain yield. Among the set of genotypes screened, IET 22218 recorded high spikelet fertility (> 85%), pollen viability (> 95%) at high temperature (39–44 °C) with relative humidity (> 60–80%). This genotype recorded higher photosynthesis, canopy temperature depression, and accumulation of endogenous level of polyamines both under optimum and heat stress environments. Moreover, IET 22218 genotype recorded lower H 2 O 2 accumulation, membrane damage and higher activity of antioxidant enzymes. Heat stress tolerance in IET 22218 was at par with heat tolerant checks, i.e., Nagina22 (N22) and Nerica L-44 (NL-44). Interestingly, IET 22218 also maintained lower chalkiness (< 34%) and higher head rice yield (> 85%) under heat stress. Based on above traits IET 22218 was selected as the novel donor for heat tolerance. The study concludes that induced polyamines and antioxidant enzymes activity in IET 22218 under stress were associated with lowering oxidative stress and maintained higher pollen viability and spikelet fertility under heat stress environment. However, more studies are recommended to understand the role of polyamines in heat stress tolerance specifically in rice.

One hundred and sixty two genotypes of different Lens species were screened for salinity tolerance in hydroponics at 40, 80 and 120 mM sodium chloride (NaCl) for 30 d. The germination, seedling growth, biomass accumulation, seedling survivability, salinity scores, root and shoot anatomy, sodium ion (Na+), chloride ion (Cl-) and potassium ion (K+) concentrations, proline and antioxidant activities were measured to evaluate the performance of all the genotypes. The results were compared in respect of physiological (Na+, K+ and Cl-) and seed yield components obtained from field trials for salinity stress conducted during two years. Expression of salt tolerance in hydroponics was found to be reliable indicator for similarity in salt tolerance between genotypes and was evident in saline soil based comparisons. Impressive genotypic variation for salinity tolerance was observed among the genotypes screened under hydroponic and saline field conditions. Plant concentrations of Na+ and Cl- at 120 mM NaCl were found significantly correlated with germination, root and shoot length, fresh and dry weight of roots and shoots, seedling survivability, salinity scores and K+ under controlled conditions and ranked the genotypes along with their seed yield in the field. Root and shoot anatomy of tolerant line (PDL-1) and wild accession (ILWL-137) showed restricted uptake of Na+ and Cl- due to thick layer of their epidermis and endodermis as compared to sensitive cultigen (L-4076). All the genotypes were scanned using SSR markers for genetic diversity, which generated high polymorphism. On the basis of cluster analysis and population structure the contrasting genotypes were grouped into different classes. These markers may further be tested to explore their potential in marker-assisted selection.

Background Alkaline soils cause low productivity in crop plants including lentil. Alkalinity adaptation strategies in lentil were revealed when morpho-anatomical and physio-biochemical observations were correlated with transcriptomics analysis in tolerant (PDL-1) and sensitive (L-4076) cultivars at seedling stage. Results PDL-1 had lesser salt injury and performed better as compared to L-4076. Latter showed severe wilting symptoms and higher accumulation of Na + and lower K + in roots and shoots. PDL-1 performed better under high alkalinity stress which can be attributed to its higher mitotic index, more accumulation of K + in roots and shoots and less aberrantly dividing cells. Also, antioxidant enzyme activities, osmolytes’ accumulation, relative water content, membrane stability index and abscisic acid were higher in this cultivar. Differentially expressed genes (DEGs) related to these parameters were upregulated in tolerant genotypes compared to the sensitive one. Significantly up-regulated DEGs were found to be involved in abscisic acid (ABA) signalling and secondary metabolites synthesis. ABA responsive genes viz . dehydrin 1, 9-cis-epoxycarotenoid dioxygenase, ABA-responsive protein 18 and BEL1-like homeodomain protein 1 had log 2 fold change above 4.0. A total of 12,836 simple sequence repeats and 4,438 single nucleotide polymorphisms were identified which can be utilized in molecular studies. Conclusions Phyto-hormones biosynthesis—predominantly through ABA signalling, and secondary metabolism are the most potent pathways for alkalinity stress tolerance in lentil. Cultivar PDL-1 exhibited high tolerance towards alkalinity stress and can be used in breeding programmes for improving lentil production under alkalinity stress conditions.

Rice productivity is severely hampered by heat stress (HS) which induces oxidative stress in this crop. This oxidative stress can be alleviated using various exogenous chemicals, including spermidine (Spd). Therefore, the present study was carried out to characterize HS components and to elucidate the role of exogenous Spd application in rice at the flowering stage. Two contrasting rice genotypes, i.e. Nagina22 (N22) and Pusa Basmati-1121 (PB-1121) were placed in temperature tunnels and exposed to HS (38-43°C) with and without Spd (1.5 mM) foliar application during the heading stage till the end of the anthesis stage. Heat stress induced the production of H O and thiobarbituric acid reactive substances, which resulted in lower photosynthesis, spikelet sterility, and reduced grain yield. Interestingly, foliar application of Spd induced antioxidant enzyme activities and thus increased total antioxidant capacity resulting in higher photosynthesis, spikelet fertility, and improved grain yield under HS in both genotypes. Under HS with Spd, higher sugar content was recorded as compared to HS alone, which maintained the osmotic equilibrium in leaf and spikelets. Spd application initiated polyamine biosynthesis, which increased endogenous polyamine levels. This study corroborates that the exogenous application of Spd is promising in induction of antioxidant defence and ameliorating HS tolerance in rice improved photosynthesis and transpiration. Thereby, the study proposes the potential application of Spd to reduce HS in rice under current global warming scenario.

In this study, 285 lentil genotypes were phenotyped under hydroponic and alkaline field conditions. Significant genotypic variation for alkalinity stress was observed among the six Lens species screened hydroponically and in the field having pH up to 9.1. The crucial parameters, like whole Na+ and K+ contents and the Na+/K+ ratio at 40 mM NaHCO3 were found significantly correlated with seedling survivability under hydroponics (r = -0.95, r = 0.93 and -0.97). Genotypes, ranked on the bases of seed yield, restricted uptake of Na+ with thick pith area, increased vascular bundles, less H2O2 production and low Na+/K+ ratio, were found important physio-anatomical traits for alkalinity stress tolerance. The proper regulation of Na+ uptake was found for maintaining higher K+. This relationship is probably the main factor responsible for a better mechanism for tolerance to high pH up to 9.1 in tolerant breeding lines PDL-1 and PSL-9 (cultivars) and ILWL-15, ILWL-192 and ILWL-20 (wild accessions). Based on UPGMA dendrogram, all the genotypes were clustered into four diverse groups. DMRT was implied within the group to differentiate genotypes based on phenotypic response under alkalinity stress. These results can be utilized for selecting diverse parents for developing alkalinity tolerant genotypes.

Rising air temperature is a major constraint for crop productivity under the current climate change scenario. Rice crops are known to be sensitive to high-temperature (HT) stress at anthesis and post-anthesis stages. Photosynthesis is an important metabolic process and is affected by HT stress. A pot study was planned to screen a set of seventy-three Indian rice accessions based upon changes in the rate of photosynthesis (Pn) and related gas exchange traits under HT, and to characterize the contrasting rice accessions for component traits of HT stress tolerance. All accessions were raised under ambient temperature (AT) until the booting stage and exposed to HT using controlled chambers at anthesis and post-anthesis. HT exposure led to a large reduction (up to 50%) in Pn, but stomatal conductance (gs) and the rate of transpiration (E) increased significantly across the rice accessions. Based on the photosynthetic response under HT, two contrasting rice accessions (IRGC 135883, tolerant, and IRGC 127222, sensitive) were selected and characterized for HT tolerance, along with an NL-44 check. Among them, Pn decreased marginally but gs and E showed significant increases under HT in the tolerant accession, while sensitive accession showed an up to 50% reduction in Pn and marginal increase in gs and E. No significant changes were recorded for chlorophyll fluorescence (Fv/Fm) in both the genotypes, but tissue temperature depression (TTD) was higher in IRGC 135883 accession under HT. Endogenous abscisic acid (ABA) content increased under HT in the flag leaf of both the accessions, and the highest increase was observed in the sensitive accession. Similarly, spikelet fertility and grain yield showed large reductions in sensitive rice accession under HT. A large increase in ABA concentration in the leaves of the sensitive rice accession might be affecting its gs and cooling capacity under an HT environment. Finally, the study concludes that tolerant rice accessions can be recommended as donors and exploited in future rice breeding programs for developing climate-resilient rice genotypes.

Aluminium (Al) stress was imposed on 285 lentil genotypes at seedling stage under hydroponics to study its effects on morpho-physiological traits where resistant cultigens and wilds showed minimum reduction in root and shoot length and maximum root re-growth (RRG) after staining. Molecular assortment based on 46 simple sequence repeat (SSR) markers clustered the genotypes into 11 groups, where wilds were separated from the cultigens. Genetic diversity and polymorphism information content (PIC) varied between 0.148-0.775 and 0.140-0.739, respectively. Breeding lines which were found to be most resistant (L-7903, L-4602); sensitive cultivars (BM-4, L-4147) and wilds ILWL-185 (resistant), ILWL-436 (sensitive) were grouped into different clusters. These genotypes were also separated on the basis of population structure and Jaccard's similarity index and analysed to study Al resistance mechanism through determination of different attributes like localization of Al and callose, lipid peroxidation, secretion of organic acids and production of antioxidant enzymes. In contrast to sensitive genotypes, in resistant ones most of the Al was localized in the epidermal cells, where its movement to apoplastic region was restricted due to release of citrate and malate. Under acidic field conditions, resistant genotypes produced maximum seed yield/plant as compared to sensitive genotypes at two different locations i.e. Imphal, Manipur, India and Basar, Arunanchal Pradesh, India during 2012-13, 2013-14 and 2014-15. These findings suggest that Al stress adaptation in lentil is through exclusion mechanism and hybridization between the contrasting genotypes from distinct clusters can help in development of resistant varieties.

Data of the tolerant and sensitive genotypes are incorrect in graphs 2014–15 Pod/Plant (% reduction)/Genotypes, 2013–14 Seed Yield/plant (% Reduction)/Genotypes, and 2014–15 Seed Yield/plant (% Reduction)/Genotypes. Percent reduction in pods and seed yield per plant in contrasting lentil genotypes grown under three salt concentrations during 2013–14 and 2014–15. https://doi.org/10.1371/journal.pone.0190462.g001 1.

Development of aluminium (Al) resistant genotypes through molecular breeding is a major approach for increasing seed yield under acidic conditions. There are no available reports on mapping of Al resistance loci and molecular breeding for Al resistant varieties in lentil. The present study reports a major quantitative trait loci (QTL) for Al resistance using simple sequence repeat (SSR) markers in F2 and F3 mapping populations derived from contrasting parents. Phenotypic response to Al was measured on the bases of root re-growth (RRG), fluorescent signals (callose accumulation) and Al contents in hydroponic assay. After screening 495 SSR markers to search polymorphism between two contrasting parents, 73 polymorphic markers were used for bulk segregation analysis. Two major QTLs were identified using seven trait linked markers, one each for fluorescent signals and RRG mapped on linkage group (LG) 1 under Al stress conditions in F2 mapping population of cross BM-4 × L-4602. One major QTL (qAlt_fs) was localised between PLC_88 and PBA_LC_373, covering 25.9 cM with adjacent marker PLC_88 at a distance of 0.4 cM. Another major QTL (qAlt_rrg) for RRG was in the marker interval of PBA_LC_1247 and PLC_51, covering a distance of 45.7 cM with nearest marker PBA_LC_1247 at a distance of 21.2 cM. Similarly, in F3 families of BM-4 × L-4602 and BM-4 × L-7903, LG-1 was extended to 285.9 and 216.4 cM respectively, having four newly developed genic-SSR markers. These QTLs had a logarithm of odd (LOD) value of 140.5 and 28.8 along with phenotypic variation of 52% and 11% for fluorescent signals and RRG respectively, whereas, qAlt_rrg had LOD of 36 and phenotypic variance of 25% in F3 population of BM-4 × L-4602. Two major QTLs identified in the present study can be further dissected for candidate gene discovery and development of molecular markers for breeding improved varieties with high Al resistance.