| Citrus is one of the most important fruit crop in the world.Seedless and late-maturing traits have always attracted the attention of citrus breeders.Recently,our research group found a seedless citrus,named ?pao‘tangerine,which has hundreds years of cultivation in Fujian Province,according to the literature recordation,Morphology observation showed that ‘Pao'tangerine possessed a sweet orange-like in fruit flesh and was similar to mandarin(Citrus reticulata)in easy peeling and ruffling fruit peel.In addition,the fruit size is similar to grapefruit.The fruit ripening period of ‘Pao'tangerine was in middle of January,and that could last until the following the middle of April.The average weight of a single fruit can be achieved 350 g.The average edible rate and soluble solids content was 45.9% and 10.4%,respectively.The average titer of titratable acid is 1.62%,and the fruit of ‘Pao' tangerine has a high juice yield.Therefore,it was valuable for us to carry a research about ‘Pao' tangerine explore the possible cause of seedless and elucidate the genetic origin mechanism.In order to study the seedless mechanism of ‘Pao'tangerine,we studied the development of pistil and the fertility of stamens,respectively.Genetic identification of ‘Pao' tangerine was performed by morphological and SSR markers.Meanwhile,we selected Satsuma orange as comparison.The results were as follows.1.Male and female gametes of ‘Pao' tangerine developmental normality(1)Observation of pollen fertility index in two consecutive years.The pollen vitality of ‘Pao' tangerine was observed by acetocarmine dyeing experiment showed that normal rate higher than 80%;cultivated the pollen of ‘Pao' tangerine on the medium,the results showed that the germination rate was higher than 75%;the amount of pollen per anther was counted using blood cell count plate,the statistics were about 2 × 104..(2)Anatomic results shown that the female gamete of ‘Pao'tangerine developed normally.The scanning electron micrographs of pollen grains indicated that the morphology structure of ‘Pao' tangerine was normal and the normality percentage of that could reached almost 80%.(3)Paraffin section observation: Observed four developmental stages of the female gamete,no abortion and deformity were found;the development of male gamete was observed and found that it did not develop abnormal.In summary,the male and female gametes of ?pao‘ tangerine developed normally,the seedless of ‘Pao' tangerine might be caused by self-incompatibility and embryo abortion2.Genetic identification of ‘Pao' tangerine(1)The UPGMA cluster analysis was carried out on 24 and 22 citrus genera and their related cultivars by 7 cp SSR and 16 nSSR markers,respectively.According to the results we could speculatethat ‘Pao' tangerine originated from an interspecific hybridization with Citrus maxima and citrus aurantium,and the former acted as female parent and the latter as male one.(2)According to the analyses of whole genome SNP datasets,we concluded that ‘Pao' tangerine could be one kind of sour orange.Although the leaf shape,fruit shape,flesh texture and color of ‘Pao' tangerine were similar to satsuma orange,there was no genetic relationship between them.(3)We also used 13 nSSR markers to preformed genetic identification research with 38 citrus genera and their related cultivars,and the result showed that ‘Pao' tangerine and ?Daidai‘ sour orange had a close genetic relationship,we could speculate that ?Daidai‘ sour orange may be one of the types of ‘Pao' tangerine or one of the hybrid parents.3.The expression of four SI-related genes was detected in different tissues of ‘Pao' tangerine using QPCRThe result showed that the expression of Cg Rns6,Cg Rns9 and Cg Rns L gene were not regular,but Cg RNS3 was specifically expressed in the pistil of ‘Pao' tangerine,which indicated that seedless reason of ‘Pao' tangerine was self-incompatibility and Cg RNS3 might be a candidate gene for self-incompatibility. |
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