Physiological and Gene-Expression Variations in Watermelon (Citrullus lanatus L.) Cultivars Exposed to Drought Stress

Abstract

Drought conditions may have direct or indirect effects on plant physiology, biochemistry, and molecular characteristics. The purpose of this study was to investigate the effects of drought stress on the physiological, biochemical, and molecular responses of three different watermelon cultivars with varying levels of drought tolerance (24: drought resistant, CS: moderately tolerant, and 98: drought sensitive). The cultivars exhibited different responses to cope with water stress according to their tolerance level. Drought induced significant reductions in chlorophyll <em>a</em>, total chlorophyll and carotenoid content and glutation reductase and ascorbate peroxidase activity in the sensitive cultivar unlike in the moderately tolerant and drought resistant cultivars. Additionally, the expression levels of <em>NAC1</em>, <em>NAC2</em>, <em>ORE1</em>, <em>WRKY24</em>, <em>SAG12</em>, <em>SAG13</em>, <em>KCS2</em>, <em>CER1</em>, <em>DREB2A</em>, <em>LTP3</em>, <em>SWEET15</em>, and <em>PYL9</em> genes were measured using qRT-PCR. The expression ratios of the genes significantly varied depending on the gene location and on the tolerance of the cultivars. Results showed that the physiology and biochemical and molecular pathways of tolerant cultivars change to adapt to drought conditions. Therefore, the drought-resistant cultivar copes with drought stress by increasing proline content and antioxidant enzyme activities, as well as by increasing the expression of specific genes.

Integrated Bulk Segregant Analysis, Fine Mapping, and Transcriptome Revealed QTLs and Candidate Genes Associated with Drought Adaptation in Wild Watermelon

“…Root and shoot architecture responses contribute to avoidance by maintaining water uptake–loss homeostasis, while tolerance is associated with transcriptomic, proteomic, and metabolic regulation, and the escape strategy is related to the shortening of the plant life cycle [ 26 ]. Several drought-mechanism studies and germplasm screenings based on leaves and roots’ responses in watermelon were reported; however, no genetic mapping investigations have been conducted yet [ 4 , 23 , 24 , 25 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ]. A strong drought-tolerance ability has mainly been observed in Citrullus amarus , Citrullus colocynthis [ 4 , 27 , 36 , 38 , 39 , 41 ], and, in some cases, wild Citrullus lanatus [ 23 , 28 , 37 , 45 , 46 ].…”

“…Several drought-mechanism studies and germplasm screenings based on leaves and roots’ responses in watermelon were reported; however, no genetic mapping investigations have been conducted yet [ 4 , 23 , 24 , 25 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ]. A strong drought-tolerance ability has mainly been observed in Citrullus amarus , Citrullus colocynthis [ 4 , 27 , 36 , 38 , 39 , 41 ], and, in some cases, wild Citrullus lanatus [ 23 , 28 , 37 , 45 , 46 ]. Interestingly, enhanced [ 23 , 28 , 38 , 41 ] and inhibited [ 37 ] root growth were defined as drought-adaptation strategies in watermelon.…”

“…Interestingly, enhanced [ 23 , 28 , 38 , 41 ] and inhibited [ 37 ] root growth were defined as drought-adaptation strategies in watermelon. Both short- and long-term (water withholding or Polyethylene Glycol (PEG) treatments) drought stress in soil or hydroponics under controlled (growth chambers), greenhouse, and field conditions at the seedling stage (1–5 leaves) were examined [ 4 , 23 , 27 , 28 , 36 , 37 , 38 , 39 , 41 , 43 , 44 , 45 , 46 ]; however, no investigation has been conducted at the post-germination stage. Specifically, four genes were described as associated with drought-stress adaptation in watermelon, namely drought-induced polypeptide (DRIP-1) [ 24 , 34 ], Ran GTPase CLRan1 [ 23 , 28 ], Cytochrome b561 (CLb561A and CLb561B) [ 32 ], and Metallothionein Type-2 ( CL MT2) [ 33 ].…”

Ecological safety and effectiveness of the growth regulator Vigor Forte and Agrovin fertilizers in the technology of growing of watermelon

“…It prefers light soils in terms of granulometric composition, and territories with significant thermal resources (the sum of temperatures is +10 0 C and more, up to 2700 ...3600 0 C). It has a long period of active vegetation [3,4,5].…”

“…But, in addition to malnutrition, abrupt changes in the external environment, such as low or high temperatures, frost, mechanical damage, chemical effects, can also lead to crop losses. Changes in phytohormones, predominance of abscisic acid, ethylene and other inhibitors over stimulating hormones leads to retardation of growth; it negatively affects the yield [3,11]. To prevent the consequences of stress, it is possible to use antistressants, which reduce the period of adaptation of plants to the influence of natural and anthropogenic factors.…”