Identification of Parental Genome Construction and Inherited Morphological Characteristics in Triploid and AneuploidIntergeneric Hybrids from a Diploid−Diploid Cross between Citrus and Fortunella

Abstract

We previously obtained two intergeneric hybrids with different ploidies, i.e., aneuploid (2n = 28) and eutriploid, from diploid−diploid crosses between ‘Kiyomi’ tangor (Citrus unshiu Marcow. × C. sinensis (L.) Osbeck) and Meiwa kumquat (Fortunella crassifolia Swingle) as novel breeding materials for a seedless kumquat. In this study, we attempted to clarify the construction of the parental genomes of these hybrids by SSR genotyping and genomic in situ hybridization (GISH)−chromomycin A3 (CMA) analysis. SSR genotyping in NSX43 (LG5) and CiBE2227 (LG8) loci revealed that both hybrids inherited one allele from ‘Kiyomi’ tangor and two heterozygous alleles from Meiwa kumquat. The GISH analysis failed due to the high genomic homology between Citrus and Fortunella. At the same time, the CMA karyotype compositions of the two intergeneric hybrids (H15-701: 2A + 1B + 3C + 13D + 7E + 1F + 1Dst; H15-702: 3A + 1B + 2C + 15D + 4E +1F + 1Dst) and both parents (‘Kiyomi’ tangor: 1A + 2B + 2C + 6D + 7E; Meiwa kumquat: 2A + 2C + 12D + 1F + 1Dst) were completely revealed. We identified the parental genome construction and polyploidization processes in both intergeneric hybrids on the basis of these SSR genotypes and CMA karyotype compositions according to the following theory: the SSR genotypes and chromosome compositions were the same as those of the somatic chromosome and two-fold after the first division (even number) in unreduced gametes caused by first-division restitution (FDR) and second-division restitution (SDR), respectively. Consequently, we determined that both intergeneric hybrids may have had two genomes derived from the 2n male unreduced gamete as a result of the FDR of the Meiwa kumquat. In addition, most horticultural traits of the leaves, flowers, and fruits of both hybrids showed intermediate traits of the parents, but the fruit sizes and flowering habits were more like those of the two inherited genomes of Meiwa kumquat.

Self-incompatibility Related to Seedless Fruit Production in <i>Citrus</i> Plants

“…This is an interesting case of competitive interactions found during the self-pollination of a diploid plant, and is likely the only example in the genus Citrus. This trait is very useful for agricultural production because unreduced gametes can be used for triploid citrus breeding (Aleza et al, 2010;Yasuda et al, 2021) and the competence of unreduced gamete production results in diploid self-compatible cultivars producing fruits with fewer seeds.…”

Morphological Characteristics, Fruit Qualities and Evaluation of Reproductive Functions in Autotetraploid Satsuma Mandarin (Citrus unshiu Marcow.)

“…6 SSR markers produced by Shimizu et al [21] were used in the present study (Table S1). PCR amplifications and electrophoresis of PCR-amplified products were carried out according to the methods described by Yasuda et al [22]. PCR amplifications were performed in a thermal controller (Biometra TAdvanced Thermocycler 96G, Analytik Jena, Jena, Germany) in a 5 µL final volume containing 0.5 ng µL −1 gDNA, 0.2 µM forward and reverse primers and 2.5 µL GoTaq Green Master Mix (Promega, Madison, WI, USA).…”