Heterotic grouping methods reveal differential breeding efficiencies and season-specific categorization of inbreds in tropical maize (Zea mays L.)

Abstract

The selection of diverse parents is a prerequisite for the exploitation of grain yield heterosis and is a real challenge to maize breeders. Heterotic grouping assists the breeder in selecting such diverse parents, which reduces the number of crosses to be made by avoiding intra-group crosses. An investigation was carried out to evaluate 54 inbreds along with two testers (LM 13 and LM14) and 108 hybrids derived using two testers with hybrid checks during the rainy and post-rainy seasons of 2019. Heterotic grouping based on three biometrical methods, viz., Specific Combining Ability combined with line Pedigree and hybrid Yield information (SCA-PY), Heterotic groups Specific and General Combining Ability (HSGCA), and Heterotic grouping by GCA of Multiple Traits (HGCAMT (HGCAMT) was inconsistent between the seasons and showed similar but not identical trends within a season. The HSGCA method could classify all the inbreds studied in both seasons. The SCA-PY and HGCAMT methods could classify 49 and 31 inbreds, respectively in the rainy season and 43 and 40 inbreds, respectively, in the post-rainy season. Only 10 inbreds were grouped identically in both seasons by all three methods and 15 inbreds were assigned to different groups between the seasons by all three methods. Besides, 44 lines (81.5%) were inconsistently grouped by at least one of the methods between the seasons, implying the season-specific response by the hybrids. The SCA-PY method was 2.2 and 6.2% more efficient than HSGCA and 10 and 18.1% more efficient than HGCAMT during rainy and post-rainy seasons, respectively. Thus, the results of the study revealed differential breeding efficiencies of grouping methods and suggested to have season-specific heterotic grouping in maize.