Morpho physiological and molecular responses of turmeric genotypes subjected to water stress

Abstract

During the turmeric crop growth, fluctuations in precipitation and seasonal changes in the crop cycle play a major role, especially water shortage, leading to yield reduction under extreme weather conditions which has become more frequent due to global climate change. However, there are no reports on the crop response and adaptation to such changes, more specifically to limited water availability during rhizome growth stage in turmeric. Understanding the mechanism by which the crop responds to drought stress will facilitate in identification/developing drought-tolerant varieties. The objective of the present study was to identify drought tolerant genotypes which produce sustainable yield under drought condition and to elucidate the physiological, biochemical and molecular mechanism involved in drought response. Morpho-physiological evaluation of 50 elite turmeric genotypes revealed that genotypes (SL 10, SL 5, IISR Prabha, IISR Prathibha, IISR Pragati, NDH 1, Suguna, Suvarna and Rajendra Sonia) with lower leaf area, higher relative water content, lesser electrolyte leakage, higher wax content and fewer stomata than other genotypes and were shortlisted as tolerant. Conversely, genotypes (IISR Alleppey Supreme, IISR Kedaram and Acc 66) with contrasting characters were selected as susceptible ones. To study the mechanism underlying drought tolerance based on physiological, biochemical and molecular characterization, these selected genotypes were maintained in pots under different soil moisture regimes viz. 100% (control), 50% (moderate stress) and 25% (severe stress) field capacities. The genotypes IISR Pragati, SL 5, Suguna, and Suvarna showed higher relative water content (RWC), enzyme activities, accumulated more free proline, sugar, phenol and protein content with lower reduction in chlorophyll, carotenoids and starch as well as lower MDA, H2O2 content and membrane leakage compared to other genotypes. Relative gene expression analysis by q-RT PCR revealed that the TFs ABF, bHLH, bZIP, NAC, DREB and WRKY were upregulated under stress condition with a higher fold change exhibited by tolerant ones. AP2 was upregulated but did not show a tolerance related variation. AQP gene was relatively more down regulated in drought tolerant genotypes under water deficit stress. These genotypes also had better yield compared to others. These four genotypes with tolerance traits and higher yield along with two susceptible genotypes (IISR Alleppey Supreme and IISR Kedaram), were further evaluated in field conditions. The results indicated that, in terms of yield anddesirable tolerance traits, the identified tolerant genotypes significantly outperformed the susceptible ones, showcasing superior drought tolerance traits. With respect rhizome quality, a notable variation was identified among different turmeric genotypes under water stress. The identified genotypes (IISR Pragati, SL 5, Suguna, and Suvarna) with better tolerance traits with sustainable yield under drought conditions can be cultivated under rainfed cultivation or areas with limited water availability during the rhizome development stage to obtain better yield with assured quality.