Abstract
Citrus is grown globally throughout the subtropics and semi-arid to humid tropics. Abiotic stresses such as soil water deficit negatively affect plant growth, physiology, biochemistry, and anatomy. Herein, we investigated the effect(s) of three water regimes (control, moderate drought, and severe drought) on the physiological and anatomical structure of 10 different citrus rootstocks with different degrees of tolerance to drought stress. Brazilian sour orange and Gadha dahi performed well by avoiding desiccation and maintaining plant growth, plant water status, and biochemical characters, while Rangpur Poona nucellar (C. limonia) and Sunki × bentake were the most sensitive rootstocks at all stress conditions. At severe water stress, the highest root length (24.33 ± 0.58), shoot length (17.00 ± 1.00), root moisture content (57.67 ± 1.53), shoot moisture content (64.59 ± 1.71), and plant water potential (−1.57 ± 0.03) was observed in tolerant genotype, Brazilian sour orange. Likewise, chlorophyll a (2.70 ± 0.06), chlorophyll b (0.87 ± 0.06) and carotenoids (0.69 ± 0.08) were higher in the same genotype. The lowest H2O2 content (77.00 ± 1.00) and highest proline content (0.51 ± 0.06) were also recorded by Brazilian sour orange. The tolerance mechanism of tolerant genotypes was elucidated by modification in anatomical structures. Stem anatomy at severe drought, 27.5% increase in epidermal cell thickness, 25.4% in vascular bundle length, 30.5% in xylem thickness, 27.7% in the phloem cell area, 8% in the pith cell area, and 43.4% in cortical thickness were also observed in tolerant genotypes. Likewise, leaf anatomy showed an increase of 27.9% in epidermal cell thickness, 11.4% in vascular bundle length, 21% in xylem thickness, and 15% in phloem cell area in tolerant genotypes compared with sensitive ones. These modifications in tolerant genotypes enabled them to maintain steady nutrient transport while reducing the risk of embolisms, increasing water-flow resistance, and constant transport of nutrients across.
Highlights
Citrus fruit crops in the family Rutaceae have the largest fruit industry globally [1,2].Rootstock choice and selection for the citrus scion variety are the most valuable decisions for growers for the implication of better yield and quality with other valuable characters.Citrus rootstock controls the physiological, biochemical, morphological, and genetic characteristics of scion cultivars grafted on selected rootstocks through the rootstock scion interaction pathway [3]
The root length of different citrus rootstocks was significantly reduced when plants were stressed with different levels of drought
Control Brazilian sour orange had the highest root length (27.67 ± 0.58 cm; pDrought × Rootstock < 0.0001), shortest root lengths were recorded by Sunki × bentake when stressed with moderate (10.33 ± 0.58 cm) or severe drought
Summary
Rootstock choice and selection for the citrus scion variety are the most valuable decisions for growers for the implication of better yield and quality with other valuable characters. Citrus rootstock controls the physiological, biochemical, morphological, and genetic characteristics of scion cultivars grafted on selected rootstocks through the rootstock scion interaction pathway [3]. Fruit juice quality and tree productivity of scion cultivars are affected by rootstock characters. Rootstock has a significant impact on nutrition, horticultural and pathological traits of citrus cultivars, growth, vigor, stress resistance, and fruit quality of the scion [4,5,6,7]. Rootstock controls translocation of water and nutrients from the soil and distributes among different up ground plant organs, which were disturbed negatively by the impact of stresses [8,9]
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