Bioactive compounds and fruit quality traits of Granny Smith Challenger apple grown under varying shade levels of green protective shade nets

Abstract

The aim of the study is to assess the yield, fruit quality, phenolic compounds, and organic acids of the Granny Smith Challenger apple (Malus x domestica Borkh.) grown under protective shade nets. In the study, control (unnetted, T1), shade nets with 15% weave (T2), 20% weave (T3), 35% weave (T4), and 55% weave (T5) were selected as treatments. In both years of the study, yield and % marketable fruit increased significantly as overall % weave resulted in shading increases. The effect of 35% weave on yield and % marketable fruit was more distinct. The highest leaf area was recorded with T5 while the highest trunk cross-section area (6.16 and 6.64 cm(2) plant(-1) in 2015 and 2016, respectively) and canopy volume (2.70 and 2.92 m(3) plant(-1)) were obtained in T3 treatment. Mass and diameter of fruit harvested from the T4 treatment (259.8 and 253.8 g, 76.3 and 74.4 mm, 92.5 and 90.3 mm in 2015 and 2016, respectively) were significantly higher than fruit of the other treatments. Fruit firmness under the protective shade netting (70.5, 71.4, 69.4, 73.1 N and 72.9, 75.6, 69.7, 72.3 N from T2 to T5 in 2015 and 2016, respectively) was significantly lower than that of the control (76.0 and 81.5 N in 2015 and 2016 respectively). As the % weave increased, the soluble solids decreased. In both years of the experiment, ferulic acid, o-coumaric and p-coumaric acid, phlorodzin, rutin and vanilic acid were significantly higher in shade-grown apples compared to control. Similarly, oxalic and fumaric acid concentrations of the apples grown in shade were significantly higher than the control fruit (3.43 and 6.34 mg kg(-1), and 2.47 and 2.73 mg kg(-1) in 2015 and 2016 respectively). Consequently, shade netting treatments had a positive effect on tree growth, yield, and fruit quality. Protective netting with 35% (T4) weave resulted in highest yield increase as well as % marketable fruit. Novelty impact statement Protective shade cloth with different % weave was studied. All shading treatments had a positive effect on tree growth, yield, and fruit quality. We found that 35% (T4) weave produced significantly higher yields of better quality, more marketable fruit.