Effects of field capacity based-irrigation levels on physiological and agronomic characteris-tics of medicinal pumpkin (Cucurbita pepo L.)

  Cucurbita pepo belongs to the Cucurbitaceae family. Drought is one of the main abiotic stresses which is limited planting in most farming land in Iran that limits produce agriculture products. Development of crops for enhanced drought resistance, among other things, requires the knowledge of physiological mechanisms and genetic control of the contributing traits at different plant developmental stages. For investigation the impact of duration of drought stress on several physiological parameters in four varieties of medicinal pumpkin (Cucurbita pepo L.), an experiment was conducted as spilt – spilt plot based on a complete randomized block design (RCBD) with three replications. The effects of water stress in five levels (S1 or control, S2 or irrigation in 75% of Field Capacity (FC), S3 or irrigation in 50% FC, S4 or irrigation in 25% FC and S5 or without irrigation (rainfed)) as main plot, four varieties that cultured in multiple points of Iran ((V1 or unknown variety from Khoy, V2 or unknown variety from Isfahan, V3 or unknown variety from Zanjan and V4 or var. Styriaca) as sub plot and during of drought stress in twelve weeks as sub subplot were considered. But for facility in analysis, only four weeks were considered. The results showed that for almost parameters, four varieties were not showed statistically differences. Since, pumpkin is not native plant in Iran, it seems these varieties have a similar genetically origin. Our results show that with increasing watering stress, seed and fruit yield and their component were reduced. Findings indicated that Relative Water Content (RWC) decreased with drought stress increasing that was agree with previous studies. In our study, total exchange gas in all four varieties when they were imposed to drought stress were changed. One of the first responses of plants to drought is stomatal closure, restricting gas exchange between the atmosphere and the inside of the leaf. The drought stress resulted in reduction of chlorophyll a, b and carotenoids. A reason for chlorophyll content reduction is that drought stress enhances the production of reactive oxygen species (ROS) such asO2 − andH2O2 that can lead to lipid peroxidation and, consequently, chlorophyll degradation (Tatrai et al., 2016). Proline contents were increased under drought stress. The proline accumulation during the stress helps the plant to reduce the oxidative destruction and it is necessary to be survived under drought stress (Verbruggen and Hermans, 2008). Our study revealed that with increasing drought stress, seed protein (%) was increased. Soluble sugar with increasing drought stress was increased. Increasing of soluble sugars during stress can be attributed to the stop of growth or synthesis in these compounds from non-photosynthesis routes (Ghorbanali, 2003). Results showed that in most traits such as fruit yield, RWC, photosynthesis and transpiration rate, stomatal conductance and carotenoids, under normal condition ‘Isfahan’ unknown variety, had the better status between other varieties in control condition. It might be stated that with increasing duration and levels of drought stress, due to keep photosynthetically conditions reduction in this variety in most traits was less than other varieties. Since, there were no significantly drought stress effects on varieties, thus we can say that “Isfahan” unknown variety is superior variety in the experiment and this variety has the capacity to introduced in Zanjan region.