Identification of Parental Chromosomes in Sexual Intergeneric Hybrid Progenies between Citrus Cultivar ‘Nanpu’ Tangor and Citropsis schweinfurthii in the Subfamily Aurantioideae

Abstract

To obtain cytogenetic information on sexual intergeneric hybrid progenies between Citropsis schweinfurthii and ‘Nanpu’ tangor (Citrus spp.), we conducted Chromomycin A₃ (CMA) chromosome banding and genomic in situ hybridization (GISH) analyses. The CMA karyotype composition of C. schweinfurthii was very simple (14D + 4E), while that of ‘Nanpu’ tangor showed more complicated chromosome types (1A + 4C + 5D + 8E). Two progenies with C. schweinfurthii as the maternal parent showed a karyotype of 1A + 1C + 11D + 5E, suggesting that each of the type A and C chromosomes was inherited from ‘Nanpu’ tangor. GISH-CMA analysis in one of these progenies showed a clear distinction between parental chromosomes, and revealed that the hybrid progeny arose due to fertilization between a female gamete with a CMA karyotype composition of 7D + 2E from C. schweinfurthii and a male 1A + 1C + 4D + 3E gamete from ‘Nanpu’ tangor. The result suggests that C. schweinfurthii had homomorphic homologous chromosomes as a wild species, while ‘Nanpu’ tangor had heteromorphic homologous chromosomes.