1. KAUTIR (Kerala Agricultural University Theses Information and Retrieval)

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    Role of Piriformospora indica in mitigating drought stress in watermelon (Citrullus lanatus (Thumb.) Mastum. & Nakai)
    (Department of Vegetable Science, College of Agriculture,Vellanikkara, 0018-03-24) Jyothymol, C P.; Sangeeta Kutty, M
    Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is a tropical crop of high economic and nutritive value that belongs to the Cucurbitaceae family. Water availability during the critical growth stages significantly influences both the yield and quality of watermelons (Nisha and Sreelathakumari, 2020). Prolonged drought stress in watermelon ultimately results in the dropping of flowers and fruits, resulting in decreased fruit yield (Mo e t al., 2016). Piriformospora indica is a beneficial root endophytic fungus that is reported to enhace plant tolerance to such abiotic as well as biotic stresses. In this study, we have evaluated the influence of P. indica in mitigating drought stress in watermelon. The study was conducted in a poly house located at the Department of Vegetable Science, COA, Vellanikkara. The experimental design was factorial CRD (Completely randomised design) with three replications and it consists of three factors each at two levels. The first factor involved in the study was variety. Two varieties namely, ‘Thar Manak’, which is the only reported drought tolerant variety of watermelon released from CIAH, Bikaner and the drought susceptible variety Sugarbaby released from IARI, were used in this study. Factor two consists of two levels of irrigation (35% field capacity and 75% field capacity). The third factor was colonization (Colonized with P. indica and non colonized with P. indica). These two varieties of watermelon were induced to soil moisture stress at different field capacities, both after colonizing with P. indica and without colonizing with P. indica. Drought stress was imposed three weeks after transplanting by gravimetric method (Mo et al., 2016). Observations were recorded after five days of drought imposition. The experiment was conducted for two seasons ie., May June and October-November. In both the seasons, all the root characters such as root length, root hypocotyl diameter, root fresh as well as dry weight was found to be significantly higher in P. indica colonized Thar Manak at 35 per cent field capacity. The vine length, shoot fresh weight and dry weight was found to be higher in P. indica colonized seedlings when compared with non-colonized ones. Highest root to shoot ratio was observed in P. indica colonized Thar Manak at 35 per cent field capacity (0.082 and 0.054 in the first and second season respectively). The results obtained over the two seasons revealed that during drought stress (35% FC), the highest transpiration rate, stomatal conductance, photosynthesis rate, instantaneous and intrinsic water use efficiency were observed in P. indica colonized seedlings of both varieties than their non-colonized seedlings. P. indica colonization has helped in lowering the rise in surface leaf temperature during drought stress. The highest RWC was observed in P. indica colonized Sugarbaby at 75 per cent field capacity (89.58 %) followed by P. indica colonized Thar Manak at 75 per cent field capacity (87.15 %) in both the seasons. Drought stress induced decrease in the leaf chlorophyll and carotenoid content was found to be lower in P. indica colonized seedlings when compared with the non colonized ones. In both seasons, the highest proline and catalase activity was observed in P. indica colonized Sugarbaby at 35 per cent field capacity. Results of DAB staining demonstrated more accumulation of harmful H2O2 in non-colonized seedlings during drought stress when compared with colonized ones. P. indica colonization has aided in enhancing the DPPH free radical scavenging activity during drought stress. It was observed that most of the treatment combinations showed significant seasonal variation in the expression of majority of this drought tolerance traits. The average temperature and relative humidity recorded during the stress period was around 41.80 ℃ and 72.00 % respectively in the first season and 43.86 ℃ and 53.60 % respectively in the second season.The varietal influence of P. indica in imparting drought stress tolerance has also been evaluated and was observed that the influence of the fungi was more pronounced in Sugarbaby. The influence of P. indica in combating drought stress was more evident in a drought susceptible variety of watermelon than a tolerant variety