Comparative study on flower bud inclusion and quality in different development stages of sweet cherry from Hangzhou and Tai’an

Abstract: 【Objective】Sweet cherry is the earliest ripening fruit in north China and mainly cultivated in Tai’an, Yantai and Dalian. South China becomes warm earlier and faster in spring than the north, so it can be earlier for marketing. Besides, sweet cherry cultivation has gradually expanded to the south due to the leisure picking market`s promoting in recent ten years. However, the introduction of sweet cherry to south is not succeeded because of the low fruiting rate, poor fruiting habits and fruit malformation. Previous studies showed that these phenomena were related to the flower organ development. Flower bud differentiation is a morphogenetic process as well as a physiological and biochemical process. The physiological differentiation of flower bud is on the basis of accumulation and synergistic effect of nutri- ents and endogenous hormones. Therefore, the development quality of flower bud is closely related to the accumulation of nutrients and endogenous hormones in trees. In this study, the differences in nutri- ent contents and endogenous hormone levels in flower buds during three stages(before dormancy, dur- ing dormancy and before budbreak) of the same sweet cherry varieties in Hangzhou and Tai’an were compared, the correlation between flower bud quality and flower bud inclusion before bud break were analyzed, in order to reveal the physiological reasons for the low quality of flower bud in Hangzhou area and provide the theoretical basis for the formulating reasonable cultivation and management mea- sures, which can be used for regulating growth and developments, and achieving stable and high yield in the future.【Methods】Five years old sweet cherry trees in Hangzhou and Tai’an were used as the ex- perimental materials. Two cultivars of sweet cherry with different chilling requirement were chosen in this study. Firstly the leaf fall and budbreak periods of two cultivars in two areas were recorded. Then, more than 30 buds from each cultivar were collected during three stages, before dormancy, during dormancy and before budbreak. The nutrient indices(such as starch content, total soluble sugar content, sol- uble protein content, reducing sugar content and free amino content) and endogenous hormones indices (such as GA3, IAA, ABA and ZRS) were determined at three stages. The flower bud index (such as longi- tudinal diameter, transverse diameter and weight) before budbreak and the floral organ quality parame- ters (such as the length of pistil and stamen, average number of flowers per cluster, diameter of ovary, stamen numbers and the embryo sac abortion rate) were investigated. Finally, multiple indicators were analyzed using the correlation analysis method and principal component analysis.【Results】The results revealed that after entering dormancy, the starch, soluble sugar and protein contents in flower bud of two sweet cherry varieties in Hangzhou area increased greatly, it reached the peak value at the stage of“during dormancy”, then decreased gradually, in which the total content of soluble sugar decreased greatly. While the reducing sugar and free amino acid contents changed little during these three stages, their contents were basically stable. Meanwhile, the contents of soluble sugar, reducing sugar and solu- ble amino acid in flower bud of two sweet cherry varieties in Tai’an area increased greatly, but the starch content decreased rapidly. From the stage of“during dormancy”to“before budbreak”, these four indices all dropped gradually, and the contents of reducing sugar, soluble amino acid and sugar dropped a lot. However, the content of soluble protein increased a little, and its content was basically stable. The study also revealed that the endogenous hormone contents in flower bud in two areas at three stages had the same trend except for ABA. But the absolute amount of a single endogenous hormone just represent- ed the metabolic level of the hormone at one stage, while the interaction between multiple hormones af- fected the entire dormancy process. Before budbreak,the ratios of ZRS/GA, ZRS /IAA, ABA/IAA, ABA/ GA and IAA/GA with HS were 0.31, 0.41, 3.31, 2.47 and 0.75, respectively. The ratios with HB were 0.28, 0.31, 2.72, 2.40 and 0.88, respectively. The ratios with TS were 0.31, 0.29, 1.7, 1.8 and 1.06, re- spectively. The ratios with HB were 0.34, 0.25, 1.46, 1.98 and 1.35, respectively. Obviously, the ratios of ZRS /GA and IAA/GA were lower than those in Tai’an area. Principle component analysis showed that the inclusions in flower bud before budbreak were TS > TB > HS > HB. The correlation analysis of the 9 indices with flower bud index displayed that at the stage of“before budbreak”, the content of solu- ble protein was positively correlated with reducing sugar, the content of starch was positively correlated with ABA but negatively correlated with soluble amino acid and IAA. The content of soluble amino ac- id was positively correlated with IAA but negatively correlated with ABA. The longitudinal diameter of flower bud was negatively correlated with the contents of starch and ABA but positively correlated with the contents of soluble amino acid and IAA. The transverse diameter of flower bud was negatively cor- related with ZRS. The weight of flower bud was positively correlated with the content of reducing sugar. The correlation analysis of 9 indices with flower organ quality displayed that at the stage before flower bud initiation, the embryo sac abortion rate was negatively correlated with the soluble protein content but positively correlated with starch content. In conclusion, the contents of nutrients and endogenous hormones before flower bud initiation were closely related to the size of flower bud and the quality of flower organ development at later stage【. Conclusion】It was obviously suggested that the storage of nu- trients in flower buds before budbreak in Hangzhou area was insufficient, and the overall level was low, especially the contents of soluble protein and reducing sugar was low, but the starch content was high, which should be the physiological reason for the low quality of flower organs in this area. Whereas with the further differentiation of flower organs after bud initiation, a series of dynamic changes of nutrient composition and endogenous hormone content still appeared, and whether this stage was more correlat- ed with the quality of flower bud development needed further study.