Study On The Reason And Countermeasure To The Poor Fruit Set Of Zuili (Prunus Salicina Lindl.)

Zuili (Prunus salicina Lindl.) is water honey type plum and an old variety in China. It has a cultivation history for 2500 years in Jiaxing of Zhejiang province. The fruit is exquisite, fresh, glossy, and become syrup liquid form after full ripe. The juice is sweet and takes wine joss-stick, the high quality of fruit flavor which the summer consumer likes. However, the unsteady fructifies and the low output puzzles its expanded reproduction seriously. Some reported that predecessors, self-infertility and adverse climatic conditions in florescence is considered as the main reason, however, no detailed data to test and verify them. Field investigation found that the rate of double-pistil flowers was high in 'Zuili', accounting for a total spending of 30-40%, and the fruit set of double-pistil flower was very low.In this study, 'Zuili' of which to study: the pollen sterility, cross compatibility and fruit setting, the development of female organ, the reason and countermeasure to double pistils by morphological and physiological means. The results were as follows:1. Study on the pollen sterility and cross compatibility in 'Zuili'. Two different maturing varieties (early and late-tape) of 'Zuili' were tested. The volume of pollen was relatively small (early-tape: 11,700 per anther, late-tape: 8330 per anther). Rate of pollen malformation were 60.4% and 54.7%, respective for early and late-tape. Pollen viability was 37.5% and 40.2% in early and late-maturing varieties. The rates of pollen germination were relatively low in two varieties, but the early varieties (14.4%) higher than late-maturing varieties (11.9%). The results of cross-pollination showed that 'Zuili' was highly self-incompatible. The pollen germination rate and pollen tube growth of 'Black Amer' in the pistil of 'Zuili' were 37.7% and 2.3μm/min, significantly higher that of 'Hongxinli' (25.8%, 1.2μm/min) and 'Mili' (27.6%, 3.0μm/min). This indicated that the compatibility of 'Black Amer' and 'Zuili' is higher than other cultivars.2. Research on female organ development process. 'Zuilil' had a single pistil, biteguminous, crassinucellate ovule. The development process of the two ovules in locule tended to be a normal developed one and the other degraded and disappeared. The embryo developed to conform the 'Solanad' type, the synergid cells were short-lived, degraded and disappeared when embryo sac matures well-formed. After fertilization, antipodal cells disintegrated quickly and disappeared. Compared to 'Black Amer', the embryo sac and embryo development of 'Zuili' lagged noticeably. In florescence, there was 50% mature embryo sac in 'Black Amer', while only 12.5% in 'Zuili'. Two weeks after bloom, the number of octant in 'Black Amer' and 'Zuili' were 75% and 25%, respectively.3. Study on the formation and countermeasure of double pistils in 'Zuili'. The double pistils can be formation during the structural differentiation stage in 'Zuili' by morphology observation of flower bud differentiation. In general, the period of flower shatter and fruit drop was within one month after pollination, however, different according to different branches. The flower abscission of annual branch occurs after one and three weeks in anthesis, and perennial branch was concentrated during 3-5 weeks after anthesis. Artificial shading increases the fruit set from 17.6% to 22.8%, twin-fruit rate dropped to 4.9% from 22.3%. Meanwhile, artificial shading made the color of leaves change deeper and reduced the tips obviously in autumn.4. Effect of gibberellic acid (GA₃) on the flowering and fruiting. Result showed that GA3 affect 'Zuili' flowering time and blossom length, but the effect was different with the processing time and concentration. Spraying 50ppm did not delay results, but good for the flower bud differentiation and shorted the process of differentiation. Flowering period of the delay to 100 ppm had the best results, in different periods of treatment can delay of four days, florescence than control extended over two days. GA3 spraying can influence the processing time for flower bud differentiation and the flowering period, and the October 9 spraying had the best results. Effect of GA3 on 'Zuili' fruit set in addition to October 9 spraying, other combinations had reduced the fruit set, and that the later we sprayed and the higher the concentration was, the lower fruit set rate it was.Based on the above test results, the poor fruit set of 'Zuili' resulted from its low pollen sterility and high self-incompatibility, so reasonable pollination tree was needed in produce. The slow embryonic development and abnormal embryo sac structure, and the amount occurrence of double-pistil were the main reason to the poor fruit set of 'Zuili'. Preliminary assessment of this was summer heat and malnutrition. Artificial shading in summer could improving the nutritional status and accommodated the temperature of the tree, so effectively reduced the occurrence of double pistils, enhanced the capacity of normal embryonic development, increasing fruit set. In addition, gibberellins applying in autumn delayed the flowering time to avoid bad weather in florescence and advanced the fruit setting.