Observation of Flower Bud Differentiation Process and Fitting of Flower Growth Model of Passion Fruit
[Objective]This study aimed to elucidate the flower bud differentiation process in the primary passion fruit(Passiflora edulis)varieties within Southern China's ecological region.Additionally,it sought to establish a flower growth model depicting the morphological differentiation of passion fruit flower buds,so as to serve as a reference for promoting and retenting passion fruit flowers.[Method]Tainong No.1(TN)as the predominant cultivar of the purple fruit variety,and Zhuangmi 05(also known as Zhuangxiangmibao,MB)as the main cultivar of the yellow fruit variety in Guangxi,China,were utilized as experimental materials.The scanning electron microscopy and paraffin section dissection were employed to observe flower bud differentiation process in these varieties.The differentiation process of nodes below the shoot apical meristem,and measured the first bract length of flower buds,leaf length,and tendril length at each node were observed too.The 7th node below the shoot apical meristem was marked as the initial marker node,and this marked the onset of the first bract differentiation phase of the flower bud.The flower bud differentiation from 0 to 16 days after marking were investigated,as well as the dynamic changes in five flower morphological indicators,such as the length of the first bract and bud from marking to flowering were tracked,for facilitating the construction of a flower growth model.[Result]The primary process of flower bud differentiation in the tested passion fruit varieties encompassed first bract formation stage,additional bract formation stage,sepal formation stage,petal formation stage,stamen formation stage,pistil formation stage,corona formation stage,etc.The duration from first bract formation to pistil formation spanned 10-12 days,with TN exhibiting 1-2 day advancement over MB.Pistil formation emerged as a vital marker for successful passion fruit flower bud development,characterized by a 3-4 mm first bract length.The duration from first bract formation to flowering ranged between 36-44 days,with TN progressing 3-4 days earlier than MB.Tendril differentiation was visible at the 4th-5th nodes below the shoot apical meristem,flower primordium differentiation at the 6th node,appearing alongside the tendril,first bract differentiation at the 7th node,vegetative meristem appearing at the 9th node,which were positioned separately on the inner side of the tendril and flower bud,axillary vegetative shoot formation at the 10th-11th nodes,and pistil primordium differentiation at the 14th-15th nodes.The non-linear regression fitting of a Logistic model in Origin software was performed for the first bract length,width,pedicle length,flower bud length,length of flower bud and pedicle along with days after making for both MB and TN,and the results showed the determination coefficient R2 ranged from 0.9524 to 0.9988,and the normalized root mean square error(nRMSE)was between 8.54%to 19.62%,indicating a good fit of the model equation.Based on the model parameters and actual observations,the length of bract entered a rapid growth period 11-12 days after marking(i.e.after the first bract formation stage)and stabilized 24-26 days after marking.Subsequently,the pedicels and sepals grew rapidly,with the sepals surpassing the bracts length,and the total length of the flower bud and pedicel entered a rapid growth phase 24-25 days after marking,blooming after reaching maximum growth at 41-42 days after marking.[Conclusion]The flower buds of passion fruit were closely associated with tendrils,and independent of nutritional buds.The flower bud differentiation and morphological differentiation of passion fruit could be divided into three stages:the first bract formation period to the pistil formation period,lasting 10-12 days;the bract growth period,lasting 12-14 days;and the flower buds and pedicels growth period,lasting 15-17 days.In actual production of passion fruit,the flowering time could be predicted using the flower growth model,and the flower bud differentiation process could be assessed using morphological indicators,such as bract length,which provided a reference basis for promoting flowering and promoting flowers.
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