Genetic diversity, population structure, and heritability of fruit traits in Capsicum annuum

Authors: Naegele, Rachel; MITCHELL, JENNA - Michigan State University; HAUSBECK, MARY - Michigan State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2016
Publication Date: 7/14/2016
Citation: Naegele, R.P., Mitchell, J., Hausbeck, M.K. 2016. Genetic diversity, population structure, and heritability of fruit traits in Capsicum annuum. PLoS One. 11(7):e0156969. doi:10.1371/journal.pone.0156969.

Interpretive Summary: In peppers, fruit shape and size are important considerations in market acceptability of new varieties. However, little is known about the heritability of fruit characteristics (e.g., size, shape, flesh thickness), which can influence success and ease of developing cultivars with desired characteristics. In addition to marketable fruit characteristics, disease resistance also is needed for cultivar success. Phytophthora capsici is a major fungal-like pathogen of cultivated pepper, causing root rot, fruit rot, and foliar blight. To better understand heritability and association of fruit characteristics with Phytophthora resistance, 116 diverse pepper lines were evaluated. Trait heritability varied greatly in the peppers evaluated, being as low as 0.56 and as high as 0.98. A score of 0 means none of the variation seen among individuals was due to genetics, while a score of 1 means all variability was due to genetics. Few fruit traits were correlated with disease resistance. However, disease susceptibility was positively correlated with both fruit size and flesh thickness. Thus, incorporating both disease resistance and certain fruit characteristics into marketable peppers may be difficult.

Technical Abstract: Cultivated pepper (Capsicum annuum) is a phenotypically diverse species grown throughout the world. Wild and landrace peppers are typically small-fruited and pungent, but contain many important traits such as insect and disease resistance. Cultivated peppers vary dramatically in size, shape, pungency, and color, and often lack resistance traits. Fruit characteristics (e.g., shape and pericarp thickness) are major determinants for cultivar selection, and their association with disease susceptibility can reduce breeding efficacy. This study evaluated a diverse collection of peppers for mature fruit phenotypic traits, correlation among fruit traits and Phytophthora fruit rot resistance, genetic diversity, population structure, and trait heritability. Significant differences within all fruit phenotype categories were detected among pepper lines. Fruit from Europe had the thickest pericarp, and fruit from Ecuador had the thinnest. For fruit shape index, fruit from Africa had the highest index, while fruit from Europe had the lowest. Five genetic clusters were detected in the pepper population and were significantly associated with fruit thickness, end shape, and fruit shape index. Genetic variation of clusters ranged from little to very great differentiation when grouped by the predefined categories. Heritability for fruit traits ranged from 0.56 (shoulder height) to 0.98 (pericarp thickness). When correlations among fruit phenotypes and fruit disease were evaluated, fruit shape index was negatively correlated with pericarp thickness, and positively correlated with fruit perimeter. Pepper fruit pericarp, perimeter, and width had a slight positive correlation with Phytophthora fruit rot, whereas fruit shape index had a slight negative correlation.