Triploid and aneuploid hybrids obtained from hybridization between Eriobotrya japonica and E. cavaleriei

Abstract

A short ripening stage, multiple large seeds per fruit, and anthracnose disease seriously restrict the loquat (Eriobotrya japonica) industry. To obtain breeding germplasm of loquat with multiple ideal traits, a wild Eriobotrya species, E. cavaleriei (2n=2x=34), which flowers in late spring and early summer and whose fruits ripen in autumn, was used as the male parent to produce triploid plants from crosses with loquat tetraploid (2n=4x=68) lines (EjK474, EjB433 and EjB456). Fifteen progenies were obtained from three hybridizations, and 13 plants were identified as hybrids according to insertion-deletion (InDel) markers. All 13 hybrids were roughly identified as triploids by flow cytometry. Therein, 4 plants were identified as aneuploids with decreased or increased chromosome numbers based on sequencing depth according to reduced-representation genome sequencing. The sequencing depth on some chromosomes of these 4 hybrids was approximately 2/3 times or 1.41 times the average depth of all detected InDel loci. Frequencies of the loquat parent-specific alleles on increased or decreased chromosomes were approximately 50% or 75%. This verified that increased or decreased alleles in the 4 hybrids were all from tetraploid parents. The fruit flesh color genotypes of all hybrids were detected; there were two red-flesh alleles and one white-flesh allele in all hybrids. Leaves of E. cavaleriei were highly resistant to anthracnose in an in vitro assay, and the leaves of loquat B433 were sensitive. Disease spot diameters on the leaves of hybrids were significantly smaller (p < 0.01) than those of B433 after infection by spores of C. gloeosporioides. Therefore, the resistance of the hybrids was greater than that of the female parent B433. All these results showed that allotriploids can be obtained via hybridization between loquat tetraploids and E. cavaleriei, with some aneuploids as secondary products. Different flowering phases and fruit ripening stages, seedlessness and resistance to anthracnose might be combined in allotriploids. This study verified that resequencing can be used to identify the molecular karyotype of interspecific hybrids.