Cluster bean is generally considered as a drought tolerant crop; few studies have shown that water stress experienced during critical growth stages can lead to substantial reduction of yield. Pot culture experiments were conducted in the Horticultural College and Research Institute for Women, Tiruchirappalli to study the response of cluster bean plants to drought and Pink Pigmented Facultative Methylotrophs (PPFM), imposed at critical growth stages, in terms of growth and yield. Cluster bean variety Pusa Navbahar seedlings were raised under pot culture conditions. In this study, six treatments were compared in varying water levels for yield enhancement in cluster bean under drought. Cluster bean seeds were inoculated with PPFM either alone or in combination with soil treatment and foliar spray. The experiment was carried out with six treatments viz., control, seed treatment (0.1%), soil application (0.2%), foliar application (0.1%), seed treatment (0.1%) + soil application (0.2%), seed treatment (0.1%) + foliar spray (0.1 %). The effect of PPFM on cluster bean growth was also examined where water supply to plants was regulated during flowering and pod filling stage. The plants were observed for germination percentage, number of leaves, leaf area, shoot length, root length, days to first flowering, days to first harvest, PPFM population on phyllosphere and rhizosphere, proline content, yield, crop duration. Results showed that the cluster bean seeds treated with PPFM (seed treatment - 0.1% + foliar spray - 0.1%) recorded the highest germination percentage (97.5 %). The same treatment also recorded the highest plant height (67.5 cm), number of leaves (20.8), leaf area (63.0 cm²) and pod yield of 102.5g/plant with the longest duration of 115 days. Though the plants grown in the low water regime produced low yield when compared to normally irrigated plants, it recorded significantly higher yield and yield components in response to PPFM application when compared to control plants maintained under drought stress. Pink Pigmented Facultative Methylotrophs (PPFM) has been identified as promising bacteria for enhanced cluster bean growth and yield probably due to the production of phytohormones. This study demonstrates that PPFM may enhance cluster bean yield in an environment characterized by soil moisture stress or low rainfall during growth period.

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