Comparison of methods for the estimation of best parent heterosis among lines developed from interspecific sunflower germplasm

Pre-breeding and elite breeding are two steps in creating high yielding sunflower hybrids that differ in well established procedures and selection methods. However, a methodology that bridge efficient use of introgression lines as product of pre-breeding procedures and their crossing to elite inbreed lines, is not yet very well established. Therefore, the development of cost- and time-efficient methods for the determination of best parent heterosis and the use of best inbred lines in crosses with introgression lines for obtaining high-yielding and stable hybrids is highly desirable. In this regard, sixteen Cytoplasmic Male Sterile (CMS) inbred lines (A) derived from four heterogeneous interspecific lines originating from three annual: H. debilis silvestris (DEB-SIL), H. praecox runyoni (PRA-RUN), H. deserticola (DES) and one perennial H. resinosus (RES) wild species were evaluated. Seven agronomic traits were measured over a period of 2 years and 38 DNA loci were analysed, in order to compare four different methods for the estimation of best parent heterosis (BPH). New inbred lines were characterized by Principal Component Analysis (PCA) of morphological traits and Principal Coordinate Analysis (PCoA) of molecular marker data. Line × tester mating design was used to evaluate General Combining Ability (GCA), while Genetic Distance (GC) estimated by markers was evaluated as a predictor of BPH by Locally Weighted Sequential Smoothing (LOESS). Analysis of combining ability is one of the most important tools breeders use to identify superior inbred lines on the basis of their performance in hybrid combinations. Results obtained in this research show that PCA of morphological and PCoA of molecular marker data on parental lines are generally in agreement with GCA effects for examined traits. GD versus BPH relationships indicate that intermediate to high GD between parental lines was optimal for best heterotic effects of most traits. In this study, we show that the combination of the PCA of morphological data, PCoA of molecular marker data and GD between parental lines is fast and affordable, giving the most important information for parental choice of introgression and elite lines in sunflower breeding programs.