In fruit production, the”twin” fruit is also called”double fruit”, which belongs to deformed fruit and defective fruit. In the production of sweet cherry, the emergence of”Gemini fruit” is one of the four major production problems in the production.”Twin fruits” affect the appearance and commodity value of fruits, and seriously hinder the production in greenhouse and efficient production in warm areas. Previous studies found that high temperature stress from June to August can lead to”twin fruits” in fruit trees, which is the key period of flower bud differentiation of sweet cherry, and is closely related to high temperature and variety differences. So far, the molecular mechanism of sweet cherry flower bud development in response to high temperature stress, forming double pistils and finally showing as”twin fruits” is not clear.
Recently, Zhang Caixi’s team from the drupe cultivation and Breeding Laboratory of Shanghai Jiaotong University in EnviroA research paper entitled”friction is involved in double fruit formation at high temperature in sweet cherry” was published on national and Experimental Botany. This study analyzed the future climate change and the incidence of”Gemini fruit” under different climate conditions, and discussed the mechanism of pavful gene and the formation of”Gemini fruit”. This study laid a theoretical foundation for exploring the molecular mechanism of the formation of”Gemini” fruit trees and breeding varieties suitable for high temperature cultivation conditions.
Previous studies have found that when the air temperature in the flower bud differentiation stage of sweet cherry is 25 ° C, almost no double pistils are formed in the flowers. Once it reaches more than 30 ° C, the number of double pistils begins to increase significantly, and a large number of double pistils are found at 35 ° C. The research team first analyzed and predicted the historical and future climate change (June to September) of China’s main sweet cherry planting areas (five sites:Yingkou, Yantai, Qinhuangdao, Tongchuan and Chengdu) and the warm reference area (Shanghai). According to the observed and predicted daily maximum temperature, during flower bud differentiation from June to September, the number of days, duration and intensity of monthly high temperature exceeding 30 ℃/35 ℃ at each observation point increased significantly, especially in southern areas such as Shanghai. It is expected that the risk of high temperature will increase in the future, and the phenomenon of”twin fruit” will become more serious, which requires the timely development of new varieties and technologies.
In order to explore the formation mechanism of double pistils in sweet cherry, the research team used paraffin sections and electron microscope scanning to detect flower buds. The flower primordium can differentiate into a single pistil (normal pistil) or two pistils (abnormal pistil) at different temperatures. The double pistil rate of Sweet Cherry Variety”meizao” under Protected Cultivation in Shanghai is about 86%, while the double pistil rate of the other five main sweet cherry producing areas is less than 10%. From July 1 to September 15, 2020, there are 64 days above 30 ° C and 54 days above 35 ° C in Shanghai, indicating that the flower bud differentiation period is under high temperature conditions.
It is well known that members of the MADS box gene family are involved in the regulation of flower bud differentiation. In order to further confirm the role of pavful in flower bud differentiation, we first heterologously expressed the”pavful” gene in Arabidopsis, resulting in a twin fruit or multi fruit phenotype. Then the functional interaction network between pavful and other proteins was predicted in the string database, and the interaction relationship between pavful and pavlfy, pavsoc1, pavap1, pavsep1 was verified by yeast two hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) experiments, which jointly participated in the flower bud differentiation process.
Present and future preventive measures
At present, the occurrence of double pistils can be reduced by artificially shading and reducing the maximum temperature during flower bud differentiation. Shading + atomization treatment showed more effective results in reducing temperature and pistil formation. In addition, the combined application of GA3 and ga3+n (nitrogen) can also reduce the formation of”Gemini”. The research team is exploring the technology of inhibiting the expression of ful through physical and chemical methods in the future to reduce the occurrence of”Gemini fruit”. At the same time, ful gene can be used as a molecular marker to screen seedlings and select varieties with low Gemini fruit rate. In 2021, the team bred and approved”Lijing” and”Jinjing” cherry varieties that are insensitive to high temperature and have extremely low twin fruit rate.
Professor Zhang Caixi of the school of agriculture and biology of Shanghai Jiaotong University is the corresponding author of this article, and Dr. Wang Jiyuan, Bo Hou and Dr. Sun Wanxia are the co authors of this article. The research was supported by the post scientist project of the national modern agricultural (peach) industry technology system and the National Natural Science Youth Fund project.