Heteroallelic diploid pollen led to self-compatibility in tetraploid cultivar 'Sha 01' (Pyrus sinkiangensis Yue)

摘要

Pear cultivar 'Sha 01' is a sport from 'Kuerlex-iangli'. Field pollination data revealed that 'Sha 01' displayed self-compatibility (SC), whereas 'Kuerlexiangli' showed self-incompatibility upon self-pollination. Reciprocal pollinations between the two varieties showed that 76% of 'Kuerlexiangli' flowers pollinated with 'Sha 01' pollen set fruit, but only 7% of 'Sha 01' flowers set fruit when pollinated with 'Kuerlexiangli' pollen. The pollen performance was monitored with fluorescence microscopy, and it was observed that 'Sha 01' accepted self-pollen but rejected 'Kuerlexiangli' pollen, whereas 'Kuerlexiangli' rejected self-pollen but accepted 'Sha 01' pollen. Taken together, 'Sha 01' showed SC as a pollen-part mutant. Molecular S-genotyping of 'Sha 01', its selfed progeny, and wild-type 'Kuerlexiangli' showed that all contained S_(22)-RNase and S_(28)-RNase alleles, but showed no nucleo-tide sequence difference or changes in transcription. After flow cytometry and chromosome number analyses, 'Sha 01' was found to be a tetraploid (2n=68) and 'Kuerlexiangli' a diploid (2n=34). Thus, the 5-genotype for 'Sha 01' was S_(22)S_(22)S_(28)S_(28) and for 'Kuerlexiangli' was S_(22)S_(28). Ploidy level of 'Sha 01' selfed progeny were also determined from leaves using flow cytometry; all seedlings were tetraploids. The 5-genotyping for the progeny was identified by S-RNase gene relative optical density for both alleles. Closer inspection of 52 progeny showed that they could be classified into three types S_(22)S_(22)S_(28)S_(28): S_(22)S_(22)S_(22)S_(28): S_(22)S_(28)S_(28)S_(28) with the distribution 28:10:14≈4:1:1; no individual homozygous for either allele was found. Therefore, it could be concluded that only heteroallelic diploid pollen S_(22)S_(28) could achieve 'Sha 01' fertilization through a so-called competitive interaction.