Mechanisms driving fruit cracking in ‘Sinhwa’ pears (Pyrus pyrifolia Nakai) and effect of foliar fertilizer application on fruit quality

Fruit cracking poses a significant challenge to 'Sinhwa' pear cultivation and has potential economic repercussions for growers due to its adverse effects on yield and fruit quality. This study delves into the phenomenon of fruit cracking in 'Sinhwa' pears by conducting a comprehensive analysis of its causes and exploring the efficacy of foliar fertilization as a mitigation strategy. To reveal the conditions contributing to fruit cracking in 'Sinhwa' pears, moisture change regimes were systematically applied to 5-year-old 'Sinhwa' trees from 2018 to 2020 during post-flowering and harvest periods. Alternating wet and dry conditions resulted in the highest fruit cracking rates, thus highlighting the importance of consistent soil moisture levels for mitigating cracking. Furthermore, the timing of fruit cracking and its histological characteristics in 'Sinhwa' pears were examined to understand the underlying causes. Microcracks appeared approximately 60 days after full bloom and preceded visible cracking, although notable changes in epidermis thickness and stone cell layer distribution were observed. Analysis of the nutrient content revealed differences in calcium and potassium levels between intact and cracked fruits, thus providing insights into potential nutritional influences on fruit quality. Potential mitigation strategies included foliar application of 0.3 % calcium chloride and 0.5 % potassium nitrate, and they demonstrated promising results in reducing fruit cracking rates compared to the control. Fruit characteristics, including mass and hardness, varied among the treatment groups, with treated trees showing notable increases in calcium content, which were correlated with decreases in fruit cracking incidence. To understand the molecular mechanisms underlying the effectiveness of foliar fertilization, gene expression levels associated with fruit cracking were analyzed by real-time PCR. Higher expression of heat-related expansion genes (Exp1 and Exp2) was observed in the treated fruits, particularly those in the calcium chloride and potassium nitrate treatments, suggesting the role of these elements in mitigating fruit cracking. This study provides valuable insights into the causes of fruit cracking in 'Sinhwa' pears and offers practical mitigation strategies, such as foliar fertilization. Moreover, the findings underscore the importance of maintaining consistent soil moisture levels and optimizing nutrient management practices to enhance fruit quality and minimize economic losses in 'Sinwha' pear cultivation.