Preliminary Study On The Degradation Mechanism Of Loquat Seeds With Different Ploidy

In recent years,we observed that under the condition of diploid loquat planting around,some triploid lines could bear fruit naturally under the condition of open pollination,and the pollen fertility and stigma fertilizability of each line were observed.the seed setting rates of different triploid lines from different varieties or the same variety were quite different.In order to explore the factors affecting the fruit setting rate of different triploid lines,and to screen the low-seed loquat with good comprehensive quality,we collected the pollen of diploid loquat varieties and artificially pollinated the triploid loquat lines with different seed setting rates.with diploid loquat as control,the ovule development at different developmental stages was observed,combined with plant endogenous hormone content determination and transcriptome analysis.To explore the important candidate genes related to the ovule development of loquat,in order to provide a theoretical basis for improving quality and efficiency in triploid loquat.The main results are as follows:1.Research on artificial pollination and seed setting48 hours after artificial pollination,the pollen tube penetration of each hybrid combination was observed by aniline blue staining test.It was found that there were more pollen grains attached to the stigma of B356 in the high yield group,and most of the pollen tubes could extend to the base of the style smoothly in the high yield group,while in the low yield group,only a small amount of pollen was successfully attached to the stigma,and the pollen tube elongation was mostly stagnated in the middle of the stigma and inhibited in the middle,and a large amount of callose deposition was observed.Under the condition of the same pollen species and pollination time,the calyx tube of high yield group B356 was obviously closed compared with low yield group A379.The results of Pearson correlation analysis between column-piercing rate and fruit-setting rate showed that there was no significant correlation between columnpiercing rate and fruit-setting rate,and the difference of column-piercing rate was not the decisive factor of fruit-setting rate.In this study,the effects of pollen species and column-piercing rate on the fruit setting rate of different lines were excluded,indicating that the seed setting rate of different lines may be related to the development of maternal sporocytes.2.Observation of ovule abortion in triploid Loquat and determination of hormone contentMorphological observation was carried out on diploid loquat Longquan NO.1,triploid loquat B356 and B357.It was found that the normal ovules of Longquan NO.1and triploid lines B356 and B357 in early fruit setting stage,fruit rapid expansion stage,hard kernel stage,color conversion stage and ripening stage were basically consistent with the change trend of loquat fruit appearance.From the early stage of fruit setting,the normal ovule was obviously different from the aborted ovule in appearance,the volume of the normal ovule was significantly larger than that of the aborted ovule,and the aborted ovule showed growth stagnation such as empty seed shape,abnormal color and so on.There was no significant difference in fruit size between B356 and B357 and Longquan NO.1,but the normal ovule size and number of B356 and B357 were significantly lower than those of diploid,and the edible rate was higher,so they were important resources for seedless loquat breeding.The contents of endogenous hormones in normal and aborted ovules of Longquan NO.1,B356 and B357 were determined.The results showed that the contents of IAA and SA in normal ovules were significantly higher than those in abortive ovules,while the contents of ACC and ABA in normal ovules were significantly lower than those in abortive ovules.The significant difference in the content of endogenous hormones in triploid loquat ovule may be one of the important inducements leading to its enucleation.3.Extraction of genes related to ovule abortion in triploid LoquatAccording to the results of endogenous hormone content determination,we selected normal ovules and aborted ovules of B356,B357 and Longquan NO.1 for transcriptome sequencing analysis,and screened out PYR/PYL genes that mediate normal ovule development and TIR1 and SAUR genes that may mediate ovule abortion.These genes may induce ovule abortion by accelerating hormone signal transduction pathway and reducing enzyme activity.To sum up,different ploidy and different varieties of loquat ovules may exercise the same set of abortion mechanism: in the plant hormone signal transduction pathway,activate or inhibit the expression of multiple components,resulting in the increase of ethylene and abscisic acid content in the ovule.The content of auxin and salicylic acid decreased,resulting in ovule abortion and even apoptosis.