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

Pear cultivar 'Sha 01' is a sport from 'Kuerlexiangli'. 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- RNase and S- RNase alleles, but showed no nucleotide sequence difference or changes in transcription. After flow cytometry and chromosome number analyses, 'Sha 01' was found to be a tetraploid (2 n = 68) and 'Kuerlexiangli' a diploid (2 n = 34). Thus, the S-genotype for 'Sha 01' was S S S S and for 'Kuerlexiangli' was S S. Ploidy level of 'Sha 01' selfed progeny were also determined from leaves using flow cytometry; all seedlings were tetraploids. The S-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 S S S: S S S S: S S S S 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 S could achieve 'Sha 01' fertilization through a so-called competitive interaction. [ABSTRACT FROM AUTHOR]