Study on fruit gummosis characteristics in Qiangcuili plum

【Objective】In order to clarify the occurrence pattern and internal regulation mechanism of fruit gummosis in Qiangcuili plum, this study systematically determined the gummosis characteristics, quality indexes, pectin components, endogenous hormones and mineral elements in different developmental stages of fruits, aiming to reveal the relationship between various factors and gummosis occurrence, and provide a theoretical basis for precise prevention and control of the disease.【Methods】15- year-old Qiangcui plum was used as the test material, and samples were taken at the critical period after flowering (70, 85, 105 and 120 days). Statistics of fruit gummosis rate and occurrence part; the appearance quality (single fruit weight, and horizontal and vertical diameters) and internal quality (soluble solids, sugar and acid contents) of normal and gummy fruits were measured and compared. The pectin was extracted by water extraction and alcohol precipitation, and its monosaccharide and amino acid composition were analyzed by the high performance liquid chromatography. The contents of endogenous hormones (jasmonic acid JA, gibberellin GA3, auxin IAA, zeatin ZA, salicylic acid SA, and abscisic acid ABA) in fruits were determined by the liquid chromatography-mass spectrometry. The contents of mineral elements (K, Ca, Mg, Fe, B and Si) in fruits were determined by the microwave digestion-inductively coupled plasma mass spectrometry and kit method. The correlation between the dynamic changes of each index and the occurrence and development of gummosis was comprehensively analyzed.【Results】The fruit gummosis began at 70 days after anthesis (DAB), and the rate of gummosis continued to increase with the development process, reaching 85% at 120 DAB. Gummosis mainly occurred in the core of fruit, accompanied by colloid accumulation, cavity formation and lignification, which seriously damaged the commodity value of fruit. Gummosis significantly affected the appearance of fruit: the single fruit weight, transverse diameter and longitudinal diameter of fruits with gummosis at mature stage (120 DAB) were 1.43 times, 1.18 times and 1.32 times of normal fruit, respectively, and these parameters increased significantly with the increase of gummosis grade. However, the effect on the content of sugar and acid in the fruit was not significant. The analysis of pectin composition showed that the water content of the gum was high (65.2%), the monosaccharide component was mainly galactose (71.89% of the total), and cystine was dominant in the amino acid component (12 520.2 mg·kg-1 , 65.37% of the total). Endogenous hormone analysis showed that there were significant differences in JA, GA3, IAA and ZA between normal fruit and gummosis fruit. The content of JA in the fruit with gummosis was significantly lower than that in normal fruit during the whole growth period (for example, it was only 1/4.87 of that in normal fruit at 120 DAB), indicating that the weakening of JA signal may be the key inducing factor of gummosis. The dynamic of mineral elements showed a clear‘early deficit-late compensation’ pattern: at the critical stage of gummosis (70 DAB), the contents of K, Ca, Mg, Fe and Si in gummosis fruits were significantly lower than those in normal fruits at the early stage of development (decreased by 28.3% to 49.12%), while the contents of K and Si in normal fruits increased during the same period. At the fruit maturity stage (120 DAB), this pattern was reversed, and most elements (K, Ca, Mg, B and Si) in the gummosis fruit showed compensatory abnormal accumulation, and the content was significantly higher than that of the normal fruit, and the Si content was as high as 4.17 times that of the normal fruit. This indicates that the periodic dynamic imbalance of K, Ca, B, Si and other elements is closely related to the occurrence of gummosis.【Conclusion】The fruit gummosis of Qiangcuili plum is a comprehensive physiological and pathological phenomenon caused by the synergistic imbalance of fruit quality traits, endogenous hormone balance and mineral element homeostasis. The 70 days after anthesis is the key threshold period for the occurrence of gummosis. The down- regulation of JA signal and the sharp deficit of key mineral elements such as K, Ca and Si constitute the core inducement of gummosis. The results revealed the physiological mechanism of gummosis, and provided a clear theoretical basis and technical target for the precise prevention and control of gummosis through nutrition regulation and hormone management in the critical period of production practice.