Marker-Assisted Selection of Male-Sterile and Maintainer Line in Chili Improvement by Backcross Breeding

Abstract

Cytoplasmic genic male sterility (CGMS) is a male sterility system that uses the maternal line for hybrid production, ensuring no obscurity of F1 seed purity and reducing the cost of hybrid seed production. Identification of the male sterility gene is important for plant improvement and classification when using the molecular marker-assisted selection (MAS) method. This study aimed to produce a new maternal line (A-line) and its maintainer line (B-line) by transferring a male-sterile line (A-line) and its maintainer line (B-line) gene from another variety to restorer lines (C-line) to achieve future hybrid seed production. In the process, the CGMS line (A-line) and B-line transferred to C1 and C3 lines, which finally resulted in new A-line (BC2F2A1 × C1, BC2F2A1 × C3), and B-line (BC1F2B1 × C1, BC1F2B1 × C3), and then used the MAS method for detecting genes and pollen viability test in the newly improved lines. The results indicated that the 3336-last2-SCAR (1639 bp) and 4162-SCAR (1046 bp) DNA markers classified the Rf locus, and the CMS-SCAR130/140 marker confirmed the S or N cytoplasm. The BC2F2A1 × C1 and BC2F2A1 × C3 lines represented both male-fertile (SRf_) and male-sterile (Srfrf) progenies in a Mendelian ratio of 3:1. Moreover, stained pollen grains with 1% acetocarmine confirmed abnormal pollen in male-sterile plants. The molecular markers that detect maintainer lines (Nrfrf) are BC1F2B1 × C1-14, BC1F2B1 × C3-10, and BC1F2B1 × C3-11. The 3336-last2-SCAR (1639 bp) and CMS-SCAR130/140 markers successfully identified the male-sterile line (Srfrf) and maintainer line (Nrfrf), and 4162-SCAR (1046 bp) detected the presence of the RfRf or Rfrf genotype in chilies at the seedling stage. The use of these markers was highly accurate and confirmed the results at the early generation stage of a conventional breeding program. It can be concluded that the CGMS and maintainer gene in chilies were successfully transferred during early generation using the backcross method.