Combining ability and hybrid selection for agronomic and nutritive value traits under two contrasting soil fertility levels in Panicum maximum Jacq.

Abstract

Panicum maximum Jacq. (sin. Megathyrsus maximus B.K. Simon & S.W.L. Jacobs) is widely cultivated in Brazil, however several growing environments have medium to low fertility soils, mainly phosphorus. Studies have shown the genetic diversity in the species for agronomic and nutritional value traits and/or attested by molecular markers. In this sense, genetic breeding strategies can be adopted for the purpose of selecting parental and/or hybrid combinations that can bring resilience and responsiveness in environments with contrasting levels of soil fertility. However, for individual selection, there is a strong demand for cost and time in phenotyping, which could be minimized by selecting individuals, using the traits of interest as visual grades, such as regrowth. Thus, the objective of this work was to estimate the general (GCA) and specific (SCA) combining abilities from partial diallel between apomictic and sexual parents of P. maximum for agronomic and nutritional value traits, under two contrasting soil fertility levels, as well as to select promising hybrids in the superior progenies of full-sibs based on the visual evaluation of regrowth capacity. Ten apomictic parents were crossed with ten sexual parents, generating 86 full-sib progenies, which were evaluated in field trials in two contrasting levels of soil fertility, named high fertility (HF) and low fertility (LF), over seven harvests. The agronomic traits total dry matter (TDMY), leaf dry matter (LDMY), leaf dry matter percentage (LDMP), density (DR) and speed of regrowth (SR) were measured, as well as the crude protein (CP), in vitro digestibility of organic matter (IVOMD) and neutral detergent fiber (NDF). There was significance for the GCA variances of parents and SCA variance of crosses regarding agronomic traits and CP, indicating the presence of genes with additive and non-additive effects in the phenotypic expression of these traits. In general, the interactions of genetic effects with soil fertility levels were significant, but without marked progeny ordering changes. Apomictic parents MP10, MP7, MP3 and MP4 and the sexual ones FP7, FP1 and FP5 were the most promising because they presented high positive estimates of GCA. The hybrid combinations FP9MP10, FP8MP7, FP1MP4 and FP1MP5 presented higher positive SCA estimates for the most relevant traits (TDMY and LDMY). Based on the selection index, 26 progenies were selected, highlighting: FP9M10, FP8MP7 and FP5MP7, in the HF and FP9M10, FP1MP4 and FP1MP5 in the LF environment. There was a higher percentage of genetic gain in progeny selection for TDMY and LDMY traits, and 78 hybrids of the 26 selected progenies were promising.