Male and female inheritance patterns in tetraploid 'Moncada' mandarin

Abstract

Tetraploid `Moncada´ mandarin, used as male and female in interploidy hybridizations, displays mainly tetrasomic inheritance for most LGs, with slight variations according to the direction of the crossing. Triploid-breeding programs in citrus are key tool to develop seedless cultivars. Obtaining triploid citrus hybrids may be achieved through different strategies, such as the exploitation of female unreduced gamete in crosses between diploid parents and diploid by tetraploid sexual hybridizations, in which tetraploid genotypes can be used as male or female parents. Genetic configuration of triploid populations from interploid crosses greatly depends on the chromosomic segregation mode of the tetraploid parent used. Here, we have analyzed the inheritance of the tetraploid 'Moncada' mandarin and compared the genetic structures of the resulting gametes when used as male and as female parent. The preferential chromosome pairing rate is calculated from the parental heterozygosity restitution (PHR) of codominant molecular markers, indicating the proportion between disomic and tetrasomic segregation. Tetraploid 'Moncada' both as female and male parent largely exhibited tetrasomic segregation. However, as female parent, one linkage group (LG8) showed intermediate segregation with tendency towards tetrasomic inheritance, while another linkage group (LG4) evidenced a clear intermediate segregation. On the other hand, when used as male parent two linkage groups (LG5 and LG6) showed values that fit an intermediate inheritance model with tetrasomic tendency. Significant doubled reduction (DR) rates were observed in five linkage groups as female parent, and in six linkage groups as male parent. The new knowledge generated here will serve to define crossing strategies in citrus improvement programs to efficiently obtain new varieties of interest in the global fresh consumption market.

Keywords: Citrus; Disomic inheritance; SSR and SNP markers; Tetraploid; Tetrasomic inheritance; Triploid.

Fig. 1

Electroferograms obtained using the CI01F04a SSR marker in: a tetraploid ‘Moncada’, b diploid ‘Anana’, c triallelic triploid hybrid MA14, d triploid hybrid MA50 with allelic dose correction using 199/210 ratio from MA14 as a baseline

Fig. 2

Distribution of PHR at the gamete level in the diploid gametes produced by tetraploid ‘Moncada’ mandarin used as female (red) or male parent (blue)

Fig. 3

Distribution of PHR at the marker level in the diploid gametes originated by tetraploid ‘Moncada’ mandarin as female (red) and male parent (blue)

Fig. 4

Dendrograms corresponding to the genetic analysis performed with SSR and SNP markers obtained by calculating the Simple Matching Dissimilarity Index and construction of the tree by weighted neighbor-joining of two populations of triploid hybrids regenerated from crosses a tetraploid ‘Moncada’ × ‘Anana’ and b ‘Clemenules’ × tetraploid ‘Moncada’. The red circle highlights the position of tetraploid ‘Moncada’. The green circle highlights the group of hybrids furthest from tetraploid ‘Moncada’