QTL mapping of male sterility and transmission pattern in progeny of Satsuma mandarin

Abstract

Seedlessness is one of the important traits in citrus breeding. Male sterility derived from Satsuma mandarin (Citrus unshiu) has been used in Japanese citrus breeding programs to obtain seedless cultivars. The efficiency of seedless cultivar breeding would be improved by developing a selection marker linked to seedlessness. In this study, we performed QTL mapping in ‘Okitsu No. 46’ × ‘Okitsu No. 56’ (O46-O56) crosses for the number of pollen grains per anther (NPG) and apparent pollen fertility (APF), two traits used as an index of male sterility, and detected a candidate QTL for NPG (MS-P1) on linkage group 8 with a significant LOD score (7.31) and 47% of variance explained. The QTL for APF (MS-F1) was detected on linkage group 6 with a significant LOD score (5.71) and 63.6% of variance explained. The role of both MS-P1 in reducing NPG and MS-F1 in decreasing APF were confirmed with the ‘Okitsu No.46’ × ‘Kara’ (O46-K) cross. Pedigree analysis inferred that both MS-P1 and MS-F1 in ‘Okitsu No. 46’ were derived from kunenbo (Citrus nobilis) through hassaku (C. hassaku) and ‘Sweet Spring’. Cytoplasm analysis revealed that both male-sterile ‘Sweet Spring’ and ‘Okitsu No. 46’ have cytoplasm derived from Kishu (C. kinokuni hort. ex Tanaka), but the cytoplasm of male-sterile kunenbo and hassaku were derived from other varieties rather than Kishu. These results suggest that MS-P1 and MS-F1 primarily reduce the NPG and decrease APF, but their expression requires a cytoplasm derived from Kishu. These findings will improve our understanding of the molecular mechanism of male sterility in citrus and help to develop a DNA marker for seedless breeding in citrus.

Segregation Distortion for Male Parents in High Density Genetic Maps from Reciprocal Crosses between Two Self-Incompatible Cultivars Confirms a Gametophytic System for Self-Incompatibility in Citrus

“…Strategies for breeding seedless varieties are based on the association of parthenocarpy and mechanisms that prevent fertilization of the ovules by pollen or results in embryo degeneration. Gametic sterility can result from sterility genes, such as the nucleocytoplasmic male sterility in Satsuma [1] or from ploidy manipulation to create triploid hybrids with unbalanced meiosis [2,3]. Self-incompatibility (SI), the inability for a male and female fertile plant to produce seeds from self-fertilization, is also an efficient way to select for seedless cultivars.…”

Parthenocarpy and Self-Incompatibility in Mandarins

“…The most marked male sterility in citrus is due to the gene-cytoplasmic interaction, as in satsumas where male sterility is associated with failed pollen grain development and scant viability [11]. Recently, two QTLs related to male sterility have been reported; MS-P1, which is a major QTL for reducing the number of pollen grains per anther and MS-F1, related to lower apparent pollen fertility [12].…”

What Does the Molecular Genetics of Different Types of Restorer-of-Fertility Genes Imply?

“…Due to its maternal inheritance, CMS is widely used in plant breeding to prepare seed parents for hybrid-seed production [1]. In other cases, CMS is a potential obstacle for crossing between a breeding line and genetic resources [4][5][6]. Controlling CMS expression is one of the major challenges in plant breeding.…”