Title : Recessive epistasis governs the interaction between apetaloid and petaloid male sterility systems in African marigold
Abstract:
Male sterility is a key genetic tool for hybrid seed production in Tageteserecta L. (African marigold), where manual emasculation is constrained by the presence of functional anthers within disc florets. Two Genic Male Sterility (GMS) systems are recognized: the apetaloid system, governed by a single recessive gene (aa) and characterized by absence of petals and stamens, and the petaloid system, controlled by a dominant gene (P_), wherein stamens are transformed into petaloid structures, resulting in double flowers and functional male sterility. While both systems are individually exploited, their genetic interaction remains unclear. Understanding such interactions is essential for integrating desirable traits from both sterility systems to enhance hybrid performance and seed production efficiency.
The present study elucidated the inheritance pattern and epistatic relationship between these systems through structured crossing and segregation analysis. Experimental material included petaloid sterile lines, apetaloid sterile lines, and fertile pure lines developed at ICAR–IIHR, Bengaluru. Crosses comprising petaloid sterile × apetaloid fertile, reciprocal combinations, male sterile × pure lines, and within-line crosses were evaluated in populations of 200 plants each. Progenies were classified into petaloid, apetaloid, fertile, and gynomonoecious types, and segregation ratios were tested using chi-square analysis.
Crosses between petaloid sterile and apetaloid fertile lines consistently yielded a 1:1 segregation of petaloid and fertile plants, with complete absence of apetaloid types. Reciprocal and apetaloid-based crosses exhibited variable segregation, including three phenotypic classes, confirming digenic control. Across populations, segregation patterns fit a 9:3:4 ratio, demonstrating recessive epistasis between two nuclear genes (A/a and P/p), wherein aa masks expression at the P locus. Petaloid sterility was expressed only in A_ backgrounds (P_), while pp conditioned fertility. Genetic heterogeneity among apetaloid lines (aapp vs. aaPp), modifier effects, and occasional gynomonoecy were also observed. The Pallele further influenced floral morphology by increasing petal whorl number in fertile backgrounds. This study defines the epistatic genetic architecture of male sterility in marigold, providing a precise framework for genotype-based parent selection and more reliable hybrid seed production.
