Studies On Flower Bud Differentiation And Occurrence Mechanism Of Wizened Bud In 'Yuluxiangli'

'Yuluxiangli' pear, an excellent and well extended new pear species, has characteristics such as large fruit, small core, high edible part, early bearing. But currently, wizened bud appeared in some regions with traits like soft, bursting and browning bud in August. With the purpose of reveal the occurrence mechanism, lowing the wizened bud amount and providing theoretical guidance to control it, we researched its physiological characteristics and cultivation techniques. The methods included observe the organizational structure of different types of flower bud at differentiation process and the key occurance time of wizened bud. Experiments were conducted to investigate the endogenous hormone contents that induced wizened bud, the changing of carbon and nitrogen nutrition and mineral nutrition during flower bud and physiology mechanism of the wizened bud. The transcriptome and differential gene expression were also analyzed in the period of wizened bud. The main results as follows:1. Cultivation measures such as nitrogen-controlling, water-controlling, branch-drooping, girdling, plant growth retardants could effectively reduced the occurrence of wizened bud.2. We observed that the soft, bursting and browning wizened bud occurred in August. Microstructure observation found that the morphological differentiation of wizened bud were normal just as the normal short shoots in undifferentiation phase, initial differentiation phase, flower bud differentiation phase. However, wizened bud initiated in middle July during the sepal differentiation phase.3. The content of indole acetic acid?IAA? in wizened bud was obviously higher than normal bud during initial periods from early June to middle June. The content of abscisic acid?ABA? in the wizened bud was significantly lower than normal bud from middle June to middle August. But the content of gibberellic acid?GA₃? was significantly higher in wizened bud. Content of the zeatin riboside ?ZR? in wizened bud were significantly higher than that in the normal pear orchard in early June. ZR/GA₃, ABA/GA₃, and ABA/ZR in buds of normal pear were significantly higher than those in the wizened bud orchards. The annual branch growth in the wizened bud appeared pear orchards were significantly higher than the normal pear orchards. Days of annual branches growth in the wizened bud pear orchard were significantly longer than normal pear orchards. Soluble sugar, starch and C/N in wizened bud were significantly lower than those in the normal bud. In wizened bud pear orchard, the branches grow faster and buds had high content of IAA, GA₃ and low content of ABA, carbohydrate, which inhibited the normal differentiation of flower buds following induced the occurrence of wizened bud.4?The contents of mineral elements were obviously different in wizened bud pear and normal pear orchards. From June 15 to August 15, contents of K, Ca, Mg, Mn and Zn of wizened bud pear were lower than normal pear orchards; Fe in the bud in the wizened bud pear were higher than normal pear orchards; Ca and Mg in the leaves in the wizened bud pear were higher than normal pear orchards; Mn and Zn in the leaves in the wizened bud pear were lower than normal pear orchards; K and Fe content of the leaves showed no significant differences in different pear orchards.5?Results showed that length and diameter of shoot growth in the wizened bud pear were significantly longer than normal pear orchards and the time of shoot stopped growing was delayed in the wizened bud pear orchard. In the period of flower bud differentiation, the content of SOD, CAT, POD and MDA in shoots of normal pear increased first then decreased subsequently. But in wizened bud pear orchard, the activity of SOD and POD showed the down trend, the activity of CAT and content of MDA were increased first then decreased subsequently. Activity of SOD, CAT and POD in the wizened bud were significantly lower than normal, but the content of MDA was significantly higher.6?The transcriptome of wizened bud and normal bud in 'Yuluxiangli' were analyzed by Illumina Hiseq2000. Compared with the Nr, KEGG, and GO databases,4.7Gb original base were identified. The unigene of non-redundant normal bud and wizened bud had 51,442 and 58,479, respectively. Among them, the unigene length under 1000 nt was 80%, equal or more than 2000 nt had about 5%, and the rest of unigene distributed between 1000-2000 nt. N50 of normal bud and wizened bud were 1,183 and 1,007, respectively. According to RPKM ?Reads per kilo-base per million reads? values, expression difference between normal bud and wizened bud was more than twice. Among these,836 unigenes were up-regulation and 948 were down-regulation. Based on GO functional annotation, 6,487 were enriched in cellular process,22,755 in moleucal_function, and 15,366 in biological regulation.952 unigene were enriched in 244 metabolic pathways based on KEGG database annotation.102 unigene were related to plant hormone signal transduction,104 unigene were carbohydrate synthesis. The expression of selected 15 DEGs RT-PCR showed no significant difference with Solexa sequencing results, which proved Solexa sequencing result, was basically reliable.In conclusion, the cultivation measures such as nitrogen-controlling, water-controlling, branch-drooping, girdling, plant growth retardants could effectively reduce the occurance of wizened bud. Wizened bud appeared during sepal differentiation phase from early July to middle July. The contents of endogenous hormone, carbon, nitrogen nutrition, mineral nutrition and reactive oxygen metabolism were unnormal in wizened bud company with different expression of relative gene, which affected the normal differentiation of flower bud and induced the happening of the wizened bud.