Factors Affecting Fruit Growth And Development Of Early-fruiting Walnut In Xinjiang

Walnut is the specialty product in Xinjiang Tarim region. With the rapid development of foresting and fruit growing, especially since 21 st century, walnut has became one of the most important fruit tree and the cultivated area has been increasing. In the area of oasis irrigation, with the conditions of lacking systematic study of nutrient and light which caused generally low and unstable production and irregular quality on Walnut. Through the investigation, we found there are three results in walnut fruit development. Fruit and flower was dropped in fruit-set period. The necrotic tissue was engulfing the basal one hundred to one-third of the kernel. The weight and volume of fruit was small. These situations result the quality of Xinjiang walnut poor. So in this study, walnut cultivated in the area of arid oasis irrigation and during the flourishing time was taken as the object, pollination experiment, carbohydrate supply test and RNA-seq technology are used to test the relationship of walnut fruit development. The purpose of this study is to explore the occurrence mechanism of precocious walnut cultivars kernel necrosis, and comprehensive understand the reason what makes walnut kernel oilness occurrence and provide theoretic basis for yield of walnut, which is the essential for the development of walnut in Xinjiang. The main research results as follows:The result showed that there were four stages in Walnut fruit development: Within 30 d after florescence(30 DAF), the weight of simple fruit, fruit longitudinal and transverse diameter grew slowly. And the embryos development went through three stages, multicellular proembryo, globular embryo, and pear-shaped embryo. There were a lot of liquid in the seed cavity by means of entity anatomy. In 30-70 DAF, the weight of simple fruit, fruit longitudinal and transverse diameter grew faster. And the embryos development went through three stages, heart-shaped embryo, torpedo-shaped embryos, and mature embryos. In 70-110 DAF, the weight of simple fruit, fruit longitudinal and transverse diameter grew slowly again. The size of walnut fruit changed a little in the next stage. The cotyledon appeared in the seed cavity, it became gelatinous or change into jelly firstly and it turn to white matter within this stage. After 110 DAF, The color of walnut hull became yellow; the fruit of walnut were maturation. In the embryo, the cell can be distinguished each other and organelles such as Vacuole, Nucleolus, Chloroplast, Starch grain, Endoplasmic reticulum, Mitochondrion; Golgi’s body appeared in cell after 30 DAF. The number of Endoplasmic reticulum was increased after 50 DAF. The tip of double membrane of Endoplasmic reticulum began to inflate and oil bodies were observed after 60 DAF. The number of oil bodies increased gradually until the fruit mature. The number of Endoplasmic reticulum decreased after 90 DAF and organelles disappeared after 110 DAF. The period of organelles which were observed in cotyledon was later than embryo. In the period of seed maturity, cells were consisted of oil bodies and protein bodies in cotyledon. Oil bodies were originated from Endoplasmic reticulum.The male flower finished microsporgenesis and development male gametophyte when the male flower buds began to dilate. There about 2.96×104 pollen grains in anther, but the pollen viability was only 27.94%, and the pollen deformity rate was 95% under TEM which connected with the meiosis abnormalities. The pistillate flower abortion might be caused by pollen with poor viability on the pistillate flowers.At the base of the locule was a single ovule. After meiosis, the megasporocytes divided into four megaspores, and 1-2 of which at chalazal end usually had functional capacity. After one cell pre-embryo divided into multicellular proembryo, which became mature eggs. The embryo sac is polygonum type.The self-pollination and cross-pollination behaviors of walnut were observed by fluorescence microscopy. The results showed that the pollen began to germinate after 8 h. The pollen tube of self-pollination and cross-pollination combination could enter the germen from 144 to 172 h and integrate with the ovule, and achieve fecundation in 240 h. The pollen tube growth of cross-pollination combination was quickest than other pollination biology.The embryos development were similar in different pollination stage. By cell divisions, unfertilized egg cells became of two cells pre-embryo, four cells pre-embryo, eight cells preembryo and till the embryo consisted of up to 8-32 cells. After the formation of a mature embryo sac, the embryo development four stage and consisted of up to several hundred cells. The abortion of walnut generally occurs in the pre-bloom, before the formation of matured eight-nucleate embryo sac, two cells pre-embryo, globular embryo, or the endosperm experienced a free nuclear stage. The proportion of abortive seeds was the highest in parthenogenesis.The dust could reduce the date of blooming phenophase. And shorten the length of stigma, reduced the secretion of stigma, which made the stigma receptivity declined. This study also demonstrated that the dust can decrease pollen germination and pollen tube growth of walnut. The dust has negative effect on pollination. The dust would have adverse impact on fruit formation; it can decrease the rate of the walnut length and diameter in rapid growth, but have no significant effect on fruit size ultimately.The fruits growth and development were difference in different source-sink ratio. The single-fruit weight, longitudinal diameter, transverse diameter are significantly different at 5% level or 1% level in different source-sink ratio(Duncan’s multiple range test). The singlefruit weight, under treatment of 1 fruit-3 leaves were raised by 16.56%,8.92% and 14.22% higher than that of 1 fruit-0 leaves, 2 fruit-0 leaves and 3 fruit-0 leaves respectively. With the same leaves, the fruits growth and development was delayed when the number of fruit increased. With the same fruit numbers, the fruits growth and development was quickened when the number of leaves increased.After Illumina sequencing, filtrated of the failure sequence, 174 545 clean reads were obtained in this research. The average length of clean reads was 644 bp per read. The total unigenes matched 94 133 unigenes with the databases of NR, NT, Swiss Prot, COG GO and KEGG, The unigenes respectively matched 69 235, 58 895, 55 687, 27 333, 51 769, 29 666 of the databases. KEGG indicated that 29 666 unigenes were mapped to 130 pathways, and 1 325 unigenes were assigned to 14 fatty biosynthesis pathways. 14 were assigned to fatty acid biosynthesis, 30 were assigned to glycerophospholipid metabolism pathway.