Abstract
BackgroundApple is one of the oldest and most valuable fruits. Water restriction is one of the major problems in the production of this fruit in some planting areas.MethodsEffects of kaolin spray treatments were studied on two early apple cultivars of Golab and Shafi-Abadi under sustained deficit irrigation (SDI) in Alborz province, Iran during 2017 and 2018. Irrigation treatments were 100%, 85%, and 70% ETc and kaolin application were concentrations of 0, 3 and 6% in 2017 and 0, 1.5 and 3% in 2018.ResultsResults showed that 85% ETc treatment compared to other irrigation treatments improved apple tree crown volume in 2017. Deficit irrigation treatments significantly reduced fruit weight in both years. Application with 6% kaolin resulted in 33.3% increase in apple fruit weight compared to non-kaolin treatment at 100% ETc irrigation in the first year. Severe deficit irrigation (70% ETc) significantly reduced apple fruit length in both years, but 6% kaolin increased fruit length in both apple cultivars in 2017. Severe deficit irrigation treatment increased the firmness of apple fruit compared to control and mild deficit irrigation (85% ETc) in the first year of experiment. There was no significant difference between irrigation treatments for apple fruit firmness in the second year of experiment. Kaolin treatments of 1.5% and 3% at full irrigation increased the soluble solids content of apple fruit by 36.6% and 44.1% in 2018, respectively. Deficit irrigation treatments significantly increased leaf proline content compared to control in both years. In the first year, kaolin treatments increased leaf proline but in the second year, leaf proline was not significant. Deficit irrigation treatment of 70% ETc and 6% kaolin had the highest amount of glycine betaine content, malondialdehyde and hydrogen peroxide in apple leaf in the first year of experiment.ConclusionsSevere deficit irrigation stress (70% ETc) increased the activity of nonenzymatic defense systems of apple trees. Kaolin as a drought stress reducing agent can be recommended in apple orchards of Golab and Shafi-Abadi cultivars as an effective and inexpensive method to improve tolerance to drought stress conditions.
Highlights
Apple is one of the oldest and most valuable fruits
Deficient irrigation at 85% ETc compared to 100% and 70% ETc treatments and 3% kaolin treatment at 85% ETc irrigation level improved apple tree crown volume in 2017 (Fig. 1)
The lowest amount of tree crown volume was observed at 6% kaolin and 70% ETc treatment in apple cultivar Shafi Abadi at (Fig. 1)
Summary
Apple is one of the oldest and most valuable fruits. Water restriction is one of the major problems in the production of this fruit in some planting areas. Severe water deficit stress decreased vegetative growth of the tree which is due to increased growth inhibitory hormones and reduced growth stimulating hormones, reduced fruit quality and the attack of plant pests [8, 9]. In the event of water stress, fruit growth decreases due to restricted cell division and cell size, while fruit firmness may be increased [10]. Significant increases in soluble solids of apple, peach and pear fruits have been observed under drought stress conditions [7, 12]. It has been shown that severe irrigation restriction at the late stages of peach fruit growth reduces fruit size, resulting in reduced yield [14]. Impaired irrigation after the onset of grape ripening showed little effect on fruit size but improved fruit compounds such as anthocyanins [15,16,17]
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