Screening Of Germplasm With High Resistance To Fruit Cracking And Primary Study On Their Resistant Mechanism In Chinese Jujube

Chinese jujube (Ziziphus jujuba Mill) is the largest nut fruit species,fruit cracking is a major phenomenon in the mature period,but the degree of the tendency is different in cultivars,so it is very important to sreen unti-cracking germplasm.This study find a group of unti-fruit cracking germplasm resourses by investigating the natural fruit cracking condition in three palces of Cangxian Germplasm Nursery of Chinese Jujube, Cangxian, Hebei,Germplasm Nursery of Chinese Jujube,Shanxi Institute of Horticulture, Taiyuan, Shanxi and National Jujube Shanxi Fruit Research institute, Taigu, Shanxi; the fruit cracking mechanism is revealed preliminary through water dynamics, water potential and microstructure of Chinese Jujube.The major results are as follows:1 The dividing system of fruit cracking in Chinese jujube were established.The fruit cracking index is divided into 6 grades based on the degree of the cracking extent:Ograde,1 grade, 2grade, 3grade, 4grade, 5grade; The ways of the fruit cracking are divided into 5 types, lengthways cracking, annular cracking, lengthways and annular cracking, lengthways+annular cracking, irregular cracking. The type of fruit cracking was stable character, there are little or no change in different growing stage, places and years.2 10 cultivars with high resistance to fruit cracking were screened.Throught two years' investigation, 10 cultivars with high resistance to fruit cracking were screened from 406 types of germplasms in Cangxian Germplasm Nursery of Chinese Jujube, Germplasm Nursery of Chinese Jujube, Shanxi Institute of Horticulture, and National Jujube Shanxi Fruit Research institute. The cultivars were Hebeilongxuzao, Chahuzao, Xuezao, Jianzao, Chuanlingzao, Huluchanghong, Chengwudongzao, Baodeyou zao, Mopanzao and Guantanzao.3 The change of water retaining rate about fruit of cultivars with different resistance to fruit crackingThe water retaining rate were higher in the early mature stage than in the late mature stage. The water retaining rate of the anti-cracking cultivars and sensitive cultivars are both very high in the early mature stage, but the water retaining rate of anti-cracking cultivars became the lowest and the sensitive cultivars became the highest in the mature stage.The cultivars with different resistance to fruit cracking were analyzed. The results showed that the water retaining rate of cultivars with different resistance increased staightly from Oh to 22h after fruit soaking in the early mature stage and then increased slowly. The water retaining rate of cultivars with the highest resistance to fruit soaking were the lowerest in the late mature stage.4 The water potential was not correlated to fruit crackingThe water potential of normal fruit and cracking fruit in the late mature stage were lower than in the early mature stage for all the cultivars, but the water retaining rate show a depressed tendency. It proved that water potential was not a major dynamic for water absorptivity of jujube fruits. The water potential was not correlated to fruit cracking in the early mature and later mature stage.5 The fruits' microstructure of cultivars with different resistance to fruit cracking were different. The fruits' microstructure of cultivars with high resistance was in order and the fruits' microstructure of cultivars with low resistance was ruleless.Through the observation of the fruits' microstructure of 8 cultivars with different resistence to fruit cracking, the fruits' microstructure of Chinese jujube could divide into two groups that include loose type and close type. The character of the loose type showed that there were more empty cells both in the outer pulp cell and the inter pulp cell, the character of the close type showed that there were less empty cells in the outer pulp cell and more empty cells in the inter pulp cell. It indicated that the two types of structure had different unti-cracking mechanism.The fruits' microstructure of cultivars with different resistance were the uniform thickness of the wax layer and epidermis layer, the regular cuticle and epidermis cells.