雷公1号柚果实无核成因探究OA

[Objective]Seedlessness is a highly desirable horticultural trait in citrus and has emerged as a major breeding target due to consumer preference for seedless fruit.Multiple mechanisms can gener-ate seedless citrus,including male sterility,female sterility,embryo abortion,and self-incompatibility.For pummelo cultivars,self-incompatibility is the predominant cause of seedlessness.Recent studies on several local pummelo varieties,such as Juxianghong pummelo,Dongshi Zaoyou pummelo,and Gongshui Baiyou pummelo,have demonstrated that their seedlessness primarily results from self-in-compatibility.Citrus self-incompatibility has been demonstrated to be a gametophytic system mediated by S-RNase,whereby pollination between identical S-genotypes fails to produce normal seeds,whereas cross-pollination between different S-genotypes yields viable seeds.The combination of self-incompati-bility and parthenocarpic ability enables stable production of seedless citrus fruit.Leigong No.1 pum-melo is an excellent local cultivar from Chenzhou,which is highly favored by consumers for its crisp flesh and distinctive flavor.However,this variety often presents a mixture of seedy and seedless fruit types in the market,which adversely affects its fresh consumption and industrial promotion.The under-lying cause of seedlessness in Leigong No.1 pummelo remains unclear.Therefore,this study aims to in-vestigate the mechanism of seedlessness in Leigong No.1 pummelo,providing a theoretical basis for stable production of seedless fruits and for seedless breeding in citrus.[Methods]Mature flowers of Leigong No.1 pummelo were dissected to examine floral organ morphology.Pollen viability was as-sessed using acetic carmine staining.Artificial emasculation was performed to evaluate the parthenocar-pic ability of Leigong No.1 pummelo.Self-pollination was conducted on Leigong No.1 pummelo,fol-lowed by cross-pollination using it as the female parent and Cocktail grapefruit,Chunxiang tangelo,and Sanhong Miyou pummelo as male parents.At 5 days post-pollination,aniline blue staining was used to observe the pollen tubes from self-pollination and cross-pollination to determine whether fertilization was successful.The number of fruits and seeds was counted to calculate the fruit set rate and the num-ber of seeds per fruit.Previously reported S-RNase-specific primers were used to identify the S-geno-type of Leigong No.1 pummelo,and semi-quantitative PCR was performed to analyze the expression pattern of S-RNase in this variety.[Results]Morphological examination of mature floral buds from Leigong No.1 pummelo revealed normal floral structures,with both pistils and stamens well devel-oped.Pollen viability assessed by acetic carmine staining was high across three consecutive years:95.51%in 2022,93.55%in 2023,and 96.50%in 2024,indicating male fertility.Artificial emasculation without pollination resulted in a fruit set rate of 14%,and all fruits were seedless,demonstrating that Leigong No.1 pummelo exhibits a certain degree of parthenocarpy.Pollination experiments were per-formed to observe pollen tube growth 5 days after pollination.The results showed that,following self-pollination,pollen grains of Leigong No.1 pummelo germinated abundantly on the stigma,but tube growth was arrested within the style,indicating self-incompatibility.In contrast,when Leigong No.1 pummelo was used as the female parent and pollinated with Cocktail grapefruit,Chunxiang tangelo,or Sanhong Miyou pummelo,pollen tubes grew normally to the base of the style,demonstrating cross-compatibility and female fertility.Statistical analysis of fruit set and seed number in Leigong No.1 pum-melo showed that the self-pollination fruit set rate was 12.00%,with an average of 0.92 seeds per fruit.All 11 seeds obtained were shriveled and abnormal,and none were able to germinate into seedlings.In contrast,cross-pollination with Cocktail grapefruit,Chunxiang tangelo,or Sanhong Miyou pummelo re-sulted in fruit set rates of 8.00%,43.94%,and 50.77%,respectively,with average seed numbers per fruit of 38.63,45.72,and 75.52.The majority of these seeds were plump and viable,capable of develop-ing into seedlings after germination and sowing.These results further confirm that seedlessness in Leigong No.1 pummelo is primarily caused by self-incompatibility.Using published primers for citrus S-RNase genes,we identified the S-genotype of Leigong No.1 pummelo as S3S5.Semi-quantitative PCR revealed that both S3-and S5-RNase alleles were weakly expressed in petals,filaments,and anthers,but exhibited strong,tissue-specific expression in pistils,including the ovary,stigma,and style,with both showing higher relative expression levels in the style than in the ovary and stigma.[Conclusion]The seedless fruit formation of the local cultivar Leigong No.1 pummelo from Chenzhou is mainly attribut-ed to the combined effects of self-incompatibility and parthenocarpy.In production practices,imple-menting isolation planting to prevent cross-pollination can achieve stable production of seedless fruits.Furthermore,the self-incompatibility in this cultivar is a gametophytic type mediated by S-RNase,with the S-genotype identified as S3S5.These results provide valuable reference data for the design of pollina-tion combinations in future seedless citrus breeding programs,facilitating the development of improved citrus varieties with reliable seedless traits.