Enhancing productivity, modifying biochemical parameters, and regulating the phenylpropanoid pathway in 'Le-Conte' pears through optimal protocatechuic acid treatments

Abstract

Background: This study aimed to investigate the impact of protocatechuic acid (PRC) treatments on the productivity and fruit quality of 'Le-Conte' pears, with a specific focus on productivity, stone cells content, and antioxidant activity. The research spanned over three consecutive cultivating seasons, with the first season serving as a preliminary study to determine the optimal PRC concentrations and the most effective number of spray applications. During the initial season, response surface methodology (RSM) was employed to optimize PRC concentration and application frequency. PRC was evaluated at concentrations ranging from 50 to 400 ppm, with treatment frequencies of either once or twice. Considering the optimal conditions obtained from RSM results, PRC treatments at 200 ppm and 300 ppm were applied twice, and their respective effects were studied in comparison to the control in the following seasons.

Results: RSM results indicated that PRC at 200 and 300 ppm, applied twice, once during full bloom and again three weeks later, yielded the most significant effects. Subsequent studies revealed that PRC treatments had a substantial impact on various aspects of fruit production and quality. Applying 300 ppm PRC once during full bloom and again three weeks later resulted in higher fruit set percentages, lower fruit abscission, and enhanced fruit yield compared to untreated trees. Additionally, the 200 ppm PRC treatment maintained physicochemical characteristics such as fruit color, increased total soluble solids (TSS), and total sugar, and maintained higher ascorbic acid content and antioxidant capacity in the fruits while reducing stone cells content and lignin. Notably, enzyme activities related to phenylpropanoid metabolism and stone cells, including phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), 4-Coumarate-CoA Ligase (4CL), cinnamyl alcohol dehydrogenase (CAD), and cinnamoyl-CoA reductase (CCR), as well as peroxidase, polyphenol oxidase, and laccase, were significantly regulated by PRC treatments.

Conclusion: Overall, this study suggests that PRC treatments are suitable for enhancing pear yield and quality, with PRC at 200 ppm being the more recommended option over 300 ppm. This approach serves as an effective strategy for achieving a balance between enhancing the productivity and fruit quality of 'Le-Conte' pears.

Keywords: Antioxidant; Fruit quality; Pre-harvest; Pyrus communis; Sustainable agriculture; Yield.

Fig. 1

Response surface plots of initial fruit set (a), fruit yield (b), total phenolic content (c), and antioxidant capacity (d) in response to PRC concentration (A), and application times (B). PRC concentrations ranging from 50 to 400 ppm were applied with different timing and repetition schemes as follows: (1) Once, at full bloom stage; (2) Once, 3 weeks after full bloom; (3) Once, 6 weeks after full bloom; (4) Twice, at full bloom stage and 3 weeks after full bloom; (5) Twice, at full bloom stage and 6 weeks after full bloom

Fig. 2

Effect of protocatechuic treatments on lignin and stone cells of 'Le-Conte' pear during 2021 (a, c) and 2022 (b, d) seasons, respectively. Vertical bars indicate the standard error of the means with different letters indicating significant variance (P ≤ 0.05) between means, as determined by Duncan's multiple range test

Fig. 3

Effect of protocatechuic treatments on total phenolics content, and antioxidant capacity of 'Le-Conte' pear during 2021 (a, c) and 2022 (b, d) seasons, respectively. Vertical bars indicate the standard error of the means with different letters indicating significant variance (P ≤ 0.05) between means, as determined by Duncan's multiple range test