Abstract
Limited information is available regarding the physiology of squash plants grown under waterlogging stress. The objectives of this study were to investigate the growth and physiological performances of three cucurbit species, Cucurbita maxima cultivar (cv.) OK-101 (OK) and Cucurbita moschata cv. Early Price (EP) and Strong Man (SM), in response to waterlogging conditions, and to develop a precise, integrated, and quantitative non-destructive measurement of squash genotypes under stress. All tested plants were grown in a growth chamber under optimal irrigation and growth conditions for a month, and the pot plants were then subjected to non-waterlogging (control) and waterlogging treatments for periods of 1, 3, 7, and 13 days (d), followed by a 3-d post-waterlogging recovery period after water drainage. Plants with phenotypes, such as fresh weight (FW), dry weight (DW), and dry matter (DM) of shoots and roots, and various physiological systems, including relative water content (RWC), soil and plant analysis development (SPAD) chlorophyll meter, ratio of variable/maximal fluorescence (Fv/Fm), quantum photosynthetic yield (YII), normalized difference vegetation index (NDVI), and photochemical reflectance index (PRI) values, responded differently to waterlogging stress in accordance with the duration of the stress period and subsequent recovery period. When plants were treated with stress for 13 d, all plants exhibited harmful effects to their leaves compared with the control, but EP squash grew better than SM and OK squashes and exhibited stronger tolerance to waterlogging and showed less injury. Changes in the fresh weight, dry weight, and dry matter of shoots and roots indicated that OK plants suffered more severely than EP plants at the 3-d drainage period. The values of RWC, SPAD, Fv/Fm, YII, NDVI, and PRI in both SM and OK plants remarkably decreased at waterlogging at the 13-d time point compared with controls under identical time periods. However, the increased levels of SPAD, Fv/Fm, YII, NDVI, and PRI observed on 7 d or 13 d of waterlogging afforded the EP plant leaf with improved waterlogged tolerance. Significant and positive correlations were observed among NDVI and PRI with SPAD, Fv/Fm, and YII, indicating that these photosynthetic indices can be useful for developing non-destructive estimations of chlorophyll content in squashes when screening for waterlogging-tolerant plants, for establishing development practices for their cultivation in fields, and for enhanced cultivation during waterlogging in frequently flooded areas.
Highlights
The Cucurbitaceae family contains 825 species derived from tropical and subtropical regions
Significant and positive correlations were observed among normalized difference vegetation index (NDVI) and photochemical reflectance index (PRI) with soil and plant analysis development (SPAD), Fv/Fm, and YII, indicating that these photosynthetic indices can be useful for developing non-destructive estimations of chlorophyll content in squashes when screening for waterlogging-tolerant plants, for establishing development practices for their cultivation in fields, and for enhanced cultivation during waterlogging in frequently flooded areas
The dry matter (DM) of Early Price (EP) squash roots was found to be higher after recovery (11.58 ± 1.69%) and in its simultaneously paired control (8.53 ± 1.62%) compared with OK squash after recovery (6.55 ± 1.10%)
Summary
The Cucurbitaceae (cucurbit) family contains 825 species derived from tropical and subtropical regions. 26 species are cultivated as vegetables [1]. The squash plant, native to Central and South America, is a creeping, climbing, herbaceous, monoecious, and annual plant [2]. The squash cultivar, Cucurbita maxima (Cma), is commonly referred to as winter squash, and is being used successfully as a cold-hardy rootstock that is resistant to chilling stress for winter production of bitter melon (Momordica charantia) [3]. Cucurbita moschata (Cmo) squash cultivar is adapted to warmer climates, mostly grown in tropical and subtropical regions, and generally more tolerant of hot and humid weather than Cma [4]. Waterlogged soil with poor drainage causes most quash cultivars to rot and to display yellow and cupping leaves [5]
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