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Cantaloupe (muskmelon) is a nutritious and commercially-important fruit crop worldwide. The fruit is naturally low in calories, fat, and sodium without any cholesterol, but is a rich source of phytochemicals (polyphenols and other antioxidants), which provide various human health benefits. Cantaloupe plants are highly productive when sufficient soil moisture is available, but are sensitive to severe water-deficit stress. Given that drought events will likely increase in the near future posing a serious threat for crop production, it is prudent to explore ways for sustainable production of cantaloupe under limited irrigation water availability. Available options for this purpose include water-efficient cultivation techniques or chemical interventions to enhance the tolerance of cantaloupe plant against drought stress. Exogenous application of salicylic acid, silicon fertilizer, and potassium nitrate could be the potential chemical options to mitigate the negative impacts of drought stress on cantaloupe.The first polyhouse experiment consisting of four silicon (Si) fertilizer doses (0, 100, 200, and 400 kg ha{u2013}1 ) applied in the form of silicic acid [H4SiO4, 20% Si content] and three soil moisture regimes (100%, 75%, and 50% field capacity [FC]) was conducted to evaluate the effects of Si on growth, yield, and fruit quality of cantaloupe under drought stress. Growth, yield, and fruit quality were significantly affected by decreasing soil moisture level. Yield and irrigation water productivity were reduced by 63{u2013}69% and 19{u2013}34%, respectively, at different Si fertilizer doses when soil moisture was reduced from 100% to 50% FC. Overall, application of Si fertilizer was beneficial at all soil moisture regimes. There was no significant difference in yield and irrigation water productivity among four Si fertilizer doses at 50% FC, while these parameters were increased by 18{u2013}27% and 16{u2013}22%, respectively, at 75% FC and by 10{u2013}19% and 2{u2013} 12%, respectively, at 100% FC with increasing Si fertilizer dose. Flesh thickness and total soluble solids content were also higher in Si-fed plants than the control. Application of silicic acid at 200 and 400 kg ha{u2013}1 maximized yield at 75% and 100% FC, respectively, and hence could be recommended as optimum doses. Selection of proper Si dose in synchronization with soil moisture level could be critical in cantaloupe production when soil moisture is a limiting factor.In the second experiment, laboratory and polyhouse studies were conducted to evaluate the effect of seed priming with potassium nitrate (KNO3) in alleviating water-deficit stress on cantaloupe. In the laboratory experiment, seeds were grown on Petri dishes after primed with 25, 50, and 100 mM KNO3 along with a non-primed control and hydropriming. Non-primed seeds had lower germination rate, germination energy, and germination rate index, while higher germination time than priming doses of 25, 50, and 100 mM KNO3. In the polyhouse experiment, cantaloupe was grown in pots subjected to five priming treatments (non-primed control, hydropriming and osmopriming with 25, 50, and 100 mM KNO3) under three soil moisture regimes (50%, 75%, and 100% FC). The results revealed a drastic reduction in fruit yield and irrigation water productivity (68% and 32%, respectively) at 50% FC compared with 100% FC. Plants grown from seeds primed with KNO3 had an overall better response than the non-primed control and hydroprimed plants. Priming dose of 100 mM KNO3 resulted in 45%, 35%, and 48% higher fruit yield than the non-primed control plants at 100%, 75%, and 50% FC, respectively. A similar trend was also observed in fruit quality parameters and irrigation water productivity. There was no difference in fruit yield and irrigation water productivity of plants raised from seed priming doses of 50 and 100 mM KNO3 at moisture-deficit conditions of 75% and 50% FC, while seed priming dose of 100 mM exhibited better results than all other priming doses when soil moisture was sufficient (100% FC). Priming seeds with optimum dose of KNO3 corresponding to the available soil moisture level might be a promising approach to maintain productivity of cantaloupe; however, seed priming with KNO3 might not produce marketable fruits under severe soil moisture deficit condition.The third polyhouse experiment consisting of six salicylic acid (SA) seed priming doses (non-primed control, 100, 200, 300, 400, and 500 ppm) and three soil moisture regimes (50%, 75%, and 100% FC) was conducted to evaluate the performance of cantaloupe. The results revealed that severe moisture-deficit condition of 50% FC drastically reduced fruit yield (64%), water productivity (48%), total soluble solids (22%), and membrane stability index (43%), while electrolyte leakage was increased by 260% at the same soil moisture regime compared with 100% FC without any SA application. Plants grown from SA primed seeds exhibited significantly better performance in terms of seed germination traits, growth, physiological, and fruit yield parameters than non primed plants across soil moister regimes. The performance of cantaloupe in terms of germination rate, root and shoot dry matter, fruit yield, water productivity, total soluble solids content, and membrane stability index was better at 300 ppm SA priming dose, which was statistically similar with 400 and 500 ppm SA doses in most cases. A consistent trend of better performance at 300 ppm SA dose, especially at severe soil moisture-deficit of 50% FC, was observed (48%, 59%, and 54% higher fruit yield, water productivity, and membrane stability index, respectively, compared with the non primed control at the same soil moisture regime). There was almost no effect of increasing SA priming dose above 300 ppm; therefore, this could be regarded as an optimum dose for maximizing productivity and economic returns when cantaloupe is grown under soil moisture-deficit conditions.The fourth polyhouse experiment evaluated the growth, fruit yield, quality, and physiological response of cantaloupe to six different combinations of Si fertilizer and KNO3 seed priming (control [without Si and KNO3], 200 kg Si ha{u2212}1, 100 mM KNO3, 200 kg Si ha{u2212}1 + 100 mM KNO3, 200 mM KNO3, and 200 kg Si ha{u2212}1 + 200 mM KNO3) under three soil moisture regimes of 50%, 75% and 100% FC. The results revealed a significant negative effect of increasing drought severity on all evaluated parameters where fruit yield, irrigation water productivity, total soluble solids, and membrane stability index were reduced by 66{u2013}77%, 31{u2013}46%, 18{u2013}31%, and 25{u2013}51%, respectively, at 50% FC compared with those at 100% FC across different treatment combinations. The combined application of Si fertilizer and KNO3 seed priming (at 200 kg ha{u2013}1 and 100 mM, respectively) was more effective than the individual application of the two, which resulted in 64{u2013}157% increase in root dry matter, 21{u2013}78% increase in fruit yield, 20{u2013}53% increase in irrigation water productivity, 17{u2013}42% increase in total soluble solids, and 10{u2013}59% increase in membrane stability index at the severe soil moisture deficit condition of 50% FC compared with other treatments. However, increasing seed priming dose of KNO3 to 200 mM in combination with 200 kg Si ha{u2013}1 largely remained ineffective as the results with 100 mM priming dose along with the same Si fertilizer dose were statistically similar. A combined application of Si at 200 kg ha{u2013}1 (40 kg ha{u2212}1 soluble Si) along with seed priming dose of 100 mM KNO3 is recommended for cantaloupe production under severe and moderate drought stress. |
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