A study was conducted to understand the influence of climatic factors on nutrient use, and whole plant water use efficiency (WUE) of hydroponically grown coconut seedlings. Two dwarf (Chowghat green dwarf, CGD and Malayan yellow dwarf, MYD) and two tall (Kalpa Pratibha, KP and Kalpatharu, KT) coconut genotypes were grown in triplicates and their water use, and biomass production were measured and WUE was analyzed across summer, monsoon and winter seasons, characterized with distinct climatic variability. In comparison to monsoon, during summer the morning temperature was (6 degrees C) high, and relative humidity (RH) was low during summer resulting in two folds increase in vapour pressure deficit on leaf surface (VPDL). Increasing VPDL had direct influence on water consumption of the plant per day which was significantly high during summer (3.14 L) compared to monsoon (1.83 L), but the difference in biomass gain was not significant. This had led to a weakly negative [R-2(144) =0.12, p < .0001] relation between water use and WUE, the WUE was only 3.35 g L-1 during summer as against 6.6 g L-1 of monsoon. The response of genotypes to increasing VPDL was also significantly different. The sensitive stomata of talls could conserve water and maintain significantly high WUE while insensitive stomata of dwarfs allowed greater water loss without a concomitant increase in biomass resulted in low WUE. The early photosynthetic light saturation at 1400 mu mole photon m(-2) s(-1) might have also contributed to low biomass production in dwarfs. This study divulges that, at high temperature and low humidity in general, coconut WUE is low and especially dwarfs are not suitable for those regions with dry weather or regions expected to become dry under future climate scenario.

Climate change has the potential to influence plant development, physiology, and distribution. Arecanut (Areca catechu L.), with its long life span of 60-70 years, thrives in a tropical habitat remains exposed to various abiotic and biotic factors. It is pertinent to comprehend the adaptation strategies of this crop towards climate change over time. The Biomod2 ensemble platform for species distribution modeling was utilized to predict the potential impact of climate change on the adaptability of the crop. The extracted study region of India was used for prediction, and the final run of 6 models ensemble includes 894 occurrence points and 9 climate variables with 80%-20% of training and validation sets. The model's outputs had area under curve (AUC) values of 0.943 and true skills statistics (TSS) of 0.741, which are regarded as accurate. The research area was categorized into five groups: very high, high, moderate, low, and very low. The examination involved assessing the shift in each category from the present to two prospective scenarios (shared socio-economic pathways; SSP 2-4.5 and SSP 5-8.5) projected for the 2050s and 2070s. A shift in the climate suitability area from 'very high' and 'high' categories to 'moderate' or 'very low' categories was observed suggesting the need for adaptive strategies to sustain the current yield levels. Amongst the regions, Karnataka state, which at present has more than 50% area under cultivation, is highly vulnerable and more area is coming under 'very low' and 'low' categories from eastern side. Meanwhile, in north eastern part of the country a shift in high suitable region from northwest to southwest is observed. Overall, the model prediction suggests that some parts of west and south interior regions of the country warrant immediate consideration in order to adapt to future climate change, whereas some part of north east can be considered for future cultivation.

Climate change and climate variability are projected to alter the geographic suitability of lands for crop cultivation. Early awareness of the future climate of the current cultivation areas for a perennial tree crop like coconut is needed for its adaptation and sustainable cultivation in vulnerable areas. We analyzed coconut's vulnerability to climate change in India, based on climate projections for the 2050s and the 2070s under two Representative Concentration Pathways (RCPs): 4.5 and 8.5. Based on the current cultivation regions and climate change predictions from seven ensembles of Global Circulation Models, we predict changes in relative climatic suitability for coconut cultivation using the MaxEnt model. Bioclimatic variables Bio 4 (temperature seasonality, 34.4%) and Bio 7 (temperature annual range, 28.7%) together contribute 63.1%, which along with Bio 15 (precipitation seasonality, 8.6%) determined 71.7% of the climate suitability for coconuts in India. The model projected that some current coconut cultivation producing areas will become unsuitable (plains of South interior Karnataka and Tamil Nadu) requiring crop change, while other areas will require adaptations in genotypic or agronomic management (east coast and the south interior plains), and yet in others, the climatic suitability for growing coconut will increase (west coast). The findings suggest the need for adaptation strategies so as to ensure sustainable cultivation of coconut at least in presently cultivated areas.

Coconut is grown along the coasts and islands that are vulnerable to climate change-induced sea level rise. Though coconut is considered moderately salt tolerant, our understanding on the growth and physiological response to sea water, either inundation or subsurface water contamination, is very limited. This understanding will enable to effectively manage coconut in coastal systems under future climatic scenarios. In this study, ten month old hydroponically grown coconut seedlings were subjected to 0, 10, 25, 50, 75 and 100 % of sea water substitution (SWS), equivalent to 2.17, 8.32, 16.32, 30.03, 42.14 and 53.69 dS m−1 EC, respectively. Substituting Hoagland solution in hydroponic system by sea water of increasing concentration (>50 % SWS) significantly changed physiological processes; Fv/Fm decreased and rs increased as early as 7 and 18 days after treatment imposition (DAT), respectively which led to significant decline in leaf area and root length expansion as early as 24 DAT. At 25 % SWS, root system (root length and root biomass) was stable but the aerial part biomass was declined by 47 %. On the other hand plant height, leaf area, collar girth and biomass accumulation of seedlings under 10 % SWS (8.32 EC) was on par with the control plants suggesting coconut seedlings could tolerate 10 % SWS. Though, PN declined by 19 % and 43 % at 10 % and 25 % SWS, respectively and a similar decline in gs without a concomitant change in leaf water potential suggested that root-generated signals regulated the stomatal movement in coconut under salinity. Still the biomass accumulation at 10 % SWS was not affected by decline in PN. Under increasing sea water treatments, most of the Na+ absorbed was compartmentalized in root and shoot, while leaf had more accumulation of K+, that ensured high K+/Na+ ratio in the leaves which is an important salinity tolerant mechanism observed in coconut. The leaf Cl− content also had strong negative correlation with [PN] (r=-0.873) and biomass (r=-0.833), therefore in addition to K+ and Na+ homeostasis, the level of tolerance to the increased Cl− content in the leaves may also play an important role in salinity tolerance of coconut. This understanding will help in making appropriate strategies for managing coconut grown at coastal systems in the face of sea level rise under climate change.

The reproductive phase of coconut is extremely sensitive to high temperature, manifesting as button (female flower) shedding and poor nut set. The progamic phase, which elapses from pollination to fertilization, is one of the most critical phases during the sexual reproduction processes in annuals and fruit trees and is extremely vulnerable to high temperature. Hence, we investigated the progamic phase of the tall coconut cultivar West Coast Tall (WCT) and the effect of high temperature on the phase under both in vivo and in vitro conditions. Coconut has a long pistil and its length was found to be 18.2 ± 4.9 mm in WCT. Pollen germination on stigma occurred one day after pollination and the pollen tube traversed through the pistil and reached micropyle of ovule four days after pollination at 29 °C. However, high temperature (Tmax > 33 °C), both under in vivo and in vitro conditions, significantly reduced pollen tube growth through the pistil, suggesting its inability to reach the ovule on time to effect fertilization. High temperature also advanced nectar secretion and stigma receptivity and the receptive stigma was dry without nectar, rendering it unappealing to insect pollinators. Thus, both poor pollination and the inability of pollen tube to reach the ovule on time to effect fertilization could be the cause of poor nut set in the coconut variety WCT under high temperature. However, it was encouraging to note that the pollen tube growth was less vulnerable to elevated temperature under high humidity, suggesting that climate change effect on coconut in coastal regions with high humidity might be less severe.

Perennials utilize complex adaptive strategies and molecular mechanisms to cope with water-deficit conditions. Hence, in order to gain molecular insights regarding water-deficit stress, two-year-old coconut seedlings of the varieties Kalpa Sree and Kalpatharu were subjected to soil water-deficit regimes (25% of available of soil moisture and control). The biochemical, physiological and growth parameters underlying water-deficit stress revealed the differential enzymatic anti-oxidants, lipid peroxidation status and water use efficiency traits between the genotypes investigated. The entire plant water use efficiency at the control condition was significantly low in Kalpatharu (4.06) compared to in Kalpa Sree (4.74). Nevertheless, under severe stress (25% ASM), Kalpatharu exhibited the highest WUE (5.68) against dwarf variety Kalpa Sree (3.84). Furthermore, the leaf transcriptome profiles of the control and water-deficit stressed seedlings were examined by utilizing paired-end RNA-Seq. In total, ~7300 differentially expressed genes have been identified between the seedlings under water-deficit stress and control. Analysis of control and stressed Kalpasree leaf transcriptome showed significant upregulation of PHLOEM PROTEIN 2-LIKE A1-like, WRKY transcription factor 40 isoform X1 and downregulation of glycerol-3-phosphate acyltransferase 3 transcripts. On the other hand, the upregulation of transcripts encoding polyamine oxidase, arabinose 5-phosphate isomerase among others and downregulation of aquaporin PIP1-2 transcript was documented in Kalpatharu leaves. Moreover, long non-coding RNA and genic SSRs were also identified from the transcriptome data to further enrich the genomic resources of coconut palm, which could pave way for its utilization in developing climate-smart coconut crop. The implications of this study in molecular dissection of the adaptive response of coconut to the soil-water deficit are also discussed.