Role of phyllosphere microbes in Ice Nucleation Activity and Its impact on drought mitigation of tomato


                              Microbes play a key role in ice nucleation that facilitates bioprecipitation, which enables the plants to survive under limited water conditions. In order to test the hypothesis, a laboratory experiment was conducted to confirm ice nucleation using two phyllosphere microorganisms viz., Pseudomonas fluorescens and pink-pigmented facultative methylotrophs (PPFM). The bioprecipitation impacts on tomatoes were assessed using a set of physiological parameters such as relative water content, stomatal conductance, leaf temperature besides colony forming unit/cm2 and tube nucleation test. A field experiment was carried out in tomato (PKM 1) involving spraying of these inoculants in 3 moisture regimes (0.6, 0.8, 1.0 IW/CPE ratio) replicated four times in a factorial RBD. The data revealed that both the microbial sprays did not significantly alter the physiological parameters of tomato with an exception of leaf temperature of P. fluorescens sprayed plants with the scheduling of irrigation at 1 IW / CPE which was significantly lower (19.7°C) than PPFM sprayed ones. On the other hand, the higher relative water content of 77.4% was registered in PPFM sprayed plants irrigated at 1.0 IW/CPE ratio. In both microbial sprays, the RWC increased progressively with the advancement of the experiment from day 1 to 10 DAS and declined thereafter. However, the average stomatal conductance of the PPFM sprayed tomato plants (0.43 mmol/m2/sec) at 15 DAS was significantly higher than P. fluorescens sprayed plant (0.34 mmol/m2/sec) under all levels of moisture regimes. The PCR amplification confirms the presence of inaW genes (ice nucleation active W gene) in P. fluorescens while it was absent in PPFM. The tube nucleation tests were proved the ice crystallization induced by the P. fluorescens. Overall, the study suggests that P. fluorescens may assist in ice nucleation activity that enables tomato plants to maintain lower leaf temperature while RWC and stomatal conductance were comparable with PPFM.

Key words : Ice nucleation, Relative water content, Pseudomonas fluorescens, PPFM, Bioprecipitation

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