PHOTOSYNTHETICA 56 (X): XXX-XXX, 2018 1 Morpho-physiological and biochemical responses of muskmelon genotypes to different degree of water deficit W.A. ANSARI *,** , N. ATRI ** , B. SINGH * , P. KUMAR *** , and S. PANDEY *,+ ICAR – Indian Institute of Vegetable Research, P.O.-Jakhani (Shahanshahpur), Varanasi (Uttar Pradesh), 221305, India * Department of Botany, M.M.V, Banaras Hindu University, Varanasi (Uttar Pradesh), 221005, India ** ICAR – Central Arid Zone Research Institute, Jodhpur (Rajasthan), 342003, India *** Abstract Morpho-physiological and biochemical analyses were carried out in eight diverse indigenous muskmelon (Cucumis melo L.) genotypes exposed to different degrees of water deficit (WD). The ability of genotypes MM-7, and especially MM-6, to counteract better the negative effect of WD was associated with maintaining higher relative water content (RWC), photosynthetic rate, efficiency of PSII, and photosynthetic pigments compare to other genotypes. Furthermore, MM-6 showed a better ability to maintain cellular homeostasis than the others. It was indicated by a stimulated antioxidative defense system, i.e., higher activities of antioxidant enzymes, accumulation of nonenzymatic antioxidants together with lower concentration of reactive oxygen species and malondialdehyde. However, the genotypes MM-2 and MM-5 suffered greatly due to WD and showed reduced RWC, photosynthetic rates, pigment content, and exhibited higher oxidative stress observed as lower antioxidant enzyme activities. Additional key words: antioxidant enzyme; muskmelon; photosynthesis; proline; reactive oxygen species. Introduction Muskmelon (Cucumis melo L.) is an important vegetable that is frequently cultivated in arid and semiarid regions, where water availability is a major limitation (Cabello et al. 2009, Ibrahim 2012). Despite being water a scarce resource in (semi)arid regions, increasing demands of industrial as well as domestic sectors, particularly in developing countries like India, are forcing a decline in water availability for agriculture. Further, the foreseen consequences of change in global climate may worsen the situation in future. This highlights the urgency for developing a new strategy to identify potential genetic resources with specific traits and technological develop- ments that can improve productivity of vegetables under declining natural resources and increasing environmental stresses (Pandey et al. 2016). Drought or water stress represents the most significant environmental constraint, limiting growth and yield efficiency of plants worldwide (Chaves et al. 2002, Adibah and Ainuddin 2011). Plants show either susceptible or tolerant response to water stress that is ascertained by interactive effects of physiological, biochemical, and morphological determinants (Penella et al. 2014). Plants exposed to WD conditions show reductions in shoot and root biomass, leaf chlorosis and necrosis, while under mild WD, these symptoms are less aparent, but various cellular processes may be altered (Dhillon et al. 2011, Kusvuran 2012). Water stress induces in plants WD and loss of cell turgor, which in turn results in stomatal closure, and ultimately retarded photosynthesis and finally also plant growth (Lawlor 2002). Besides, at the cellular level, WD results in enhanced generation of reactive oxygen species (ROS), such as superoxide radicals (O 2 ¯ ), ——— Received 19 June 2017, accepted 22 November 2017. + Corresponding author; phone: +91-0542-2635247; fax : +91-05443-229007, e-mail: sudhakariivr@gmail.com, Sudhakar.Pandey@icar.gov.in Abbreviations: APX – ascorbate peroxidase; Car – caroteinods; CAT – catalase; DM – dry mass; DMRT – Duncan’s multiple range tests; DWD – days of water deficit; EL – electrolyte leakage; FM – fresh mass; Fv/Fm – maximal quantum yield of PSII photochemistry; GR – glutathione reductase; gs – stomatal conductance; MDA – malondialdehyde; PN – net photosynthetic rate; POD – guaiacol peroxidase; RWC – relative water content; SOD – superoxide dismutase; SWC – soil water content; WD – water deficit; WW – well watered. Acknowledgements: The authors acknowledge the generous support of the National Agricultural Innovation Project (NAIP), New Delhi. We thank Dr. A.B. Singh for guidance during the data collection. A Maulana Azad National Fellowship provided to WAA by the University Grant Commission (UGC), New Delhi, India, is fully acknowledged. The authors declare that there is no conflict of interest.