Research In Mechanism And Factors Of Fruit Cracking Of Ziziphus Jujuba

Fruit cracking is one of the serious problems in the development of jujube (Ziziphus jujuba Mill.) industry in China. Exploring the mechanisms underlying jujube fruit cracking is essential for the development of new cultivar with high cracking resistance and also provides important reference to overcome the problem. This study investigated the natural fruit cracking condition in Germplasm Nursery of Chinese Jujube in Cangxian, Hebei. Four cultivars were chosen in this study, among which ’Muzao205’and’Longxuzao63’were cracking resistance types and ’Mayazao35’ and ’Meimizao59’ were susceptible types. And, the hybrid seedlings between ’Dongzao’ and ’Linyilizao’(in Ren Xian, Hebei) were chosen to investigate of the rate of fruit cracking and to reveal the anatomy structure through the paraffin section analysis.The factors affected fruit cracking are investigated through biomechanics of the fruit, morphology and component analysis of fruit cuticle. The major results were as follows:TA.XT plus texture analyser was used to perform the puncture test with the fresh fruits for biomechanics of the four cultivars jujube fruit. The results were showing that in the middle of fresh fruits, there was a significant negative correlation between pericarp break force, flesh firmness and cracking index; and there was a extremely significant positive correlation between fruit uniformity index (P=2) and cracking index. In the top of fresh fruits, there was a negative correlation between pericarp break force, pericarp toughness, flesh firmness and cracking index; and there was a extremely significant positive correlation between fruit uniformity index (P=10) and cracking index. The texture at different parts of the fruits of same cultivar was not even. Hence we may presumed that fruits’texture was one of the factors affect fruit cracking.Half-red period of fresh fruits were chosen to reveal fruit epidermal anatomy structure through the paraffin section analysis. The results showed that there was an extremely significant negative correlation between the thickness of fruit epidermal cells and cracking rate. The fruit of cracking resistant type had tighter arrangement of epidermis cells than that of cracking sensitive type. The anticlinal pegs in layer epidermis cells caused by cuticle deposition were obvious in the fruit of resistant cracking type, which did not appear in the cracking susceptible type.Fourier transform infrared (FTIR) analysis of isolated cuticle of half-red period of fresh jujube fruits revealed higher levels of saturated fatty ester (C=O), the carbonyl of ester (C=O),(C=C), acidamide, aromatic acid esters (C-O-C) in the susceptible cracking type than the resistant cracking type.GC-MS was used to analyze the components of wax and cutin isolated cuticle of half-red period of fresh jujube fruits. The primary results showed the main components of wax extracted from isolated cuticle of jujube were the middle long and very long C chain compounds.All components of C16of cutin in cracking resistance type were higher than susceptible types, but some components of C18was opposite of C16.In this study, the differences of fruit cracking characteristic in different cultivars of jujube were investigated through biomechanics and compounds of fruit cuticle, to reveal fruit cracking mechanism. The results laid a foundation for the research on fruit cracking mechanism based on the cuticle formation and properties.