Study of Bud Differentiation in Hayward and Tomuri Cultivars of Kiwifruit

Document Type : Research Article


1 University of Zanjan

2 Citrus and subtropical Research Center, AREEO, Ramsar


Introduction: It is important to understand the structural events associated with flower morphogenesis in horticultural plants, because it has many aspects of practical horticultural significance. Information about different stages of flower initiation and development is important for better management of the vineyardsand fruit set. Knowledge of floral ontogeny in kiwifruit is also important for the establishment of breeding programs and for the understanding of the evolutionary processes involved in the development of the floral organs. The main objective of this study was documentation of the differentiation stages of flower buds for better understanding of morphological and external changes in (Actinidiadeliciosa[A. Chev.] C.F. Liang &A.R. Ferguson var.deliciosa) cvs.Hayward (female) and Tomuri (male).
Materials and Methods: The experiment was carried out over two years in a mature 'Hayward' and ‘Tomuri’ kiwifruit vineyard at the Citrus and Subtropical Research Center of Iran (Ramsar city). Pistillate and staminate flowers development was followed from the stage of undifferentiated primordia, present in the axils of leaf primordia in dormant buds since mid-March to early June 2015 and 2016. Equally buds in diameter and size from sixth to twentieth buds on one-year old cane of Hayward and Tomuri selected at 5 to 7 days intervals. They were sampled and fixed in a solution of formalin, ethanol 70%, glacial acetic acid (2:5:1 FAA) then stored in refrigerator. Fifteen buds of each sample dissected under a Nikon SMZ645 stereo zoom microscope. The very dense pubescence within the buds was removed manually without damaging the axillary flower primordia. The remaining pubescence was removed using dissecting needles. Various stages of flower differentiation were explained with principal growth stage 5 of BBCH scale.
Results and Discussion: The first signs of the flower on Tomuri were observed 2 days before bud swelling stage (01), on the March 12th, about one month before bud break in 2015. While in the Hayward variety the first signs of the flower primordia were observed on the March 21th of 2015 (9 days later). At the beginning of bud swelling (01), flower primordia begin to differentiation and at advanced bud swelling stage (03), bracts and sepals initiated. As development proceeded, different parts of flowers initiated acropetally. Lateral flowers were formed in the bud break (07), before initiation of petals. In advanced budburst stage (09) stamen primordia appear almost immediately after petal initiation, as two whorls in 'Hayward' and as three whorls in the Tomuri cultivar. Stigma initiated in the open cluster stage (10) in Hayward cultivar about 24-25 days after bud swell stage. The process of differentiation of buds and reproductive organs in the second year was the same as the first year with the exception that differentiation began earlier than that in the first year. Climatic conditions were affected flower development and in the second year primordia differentiation began earlier two days in Tomuri and six days in Hayward than those in the first year. The advanced budburst stage (09) in Tomuri 9 days and in the Hayward 10 days was occurred earlier than that in the first year. Unlike other tree fruits, flower induction in the kiwifruit occurred about 6 months before flower initiation. Flower primordia differentiation initiated shortly before bud break stage and approximately two months before full bloom. Flower initiation and differentiation time may be partly estimated with external changes of buds development. According to cultivar, chilling and heat requirements and climatic conditions during the research, flower initiation and differentiation period have fluctuation. A reason for the difference between the development stages and different varieties can be caused by the chilling and heat requirements. The more heat requirement, the longer reproductive meristem differentiation period.
Conclusion: An understanding of the flower initiation and development is very important for the research and management of fruit trees. A knowing of flower initiation and differentiation can be developed corrective vineyard management and practices in crisis period and prepared breeding programs. Tomuri initiated and developed their floral organs earlier than those in Hayward. Different external changes in the bud may be partly used to estimate of flower development status. The results showed that flower initiation and differentiation in buds coincided with the beginning of development and elongation of bud in the early of spring.


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