Abnormalities in juvenile‐to‐adult transition are associated with hybrid weakness in chili pepper (Capsicum)

Weakness was observed in the F1 hybrids of crosses between Capsicum annuum × Capsicum chinense or C. annuum × Capsicum frutescens. This phenomenon is morphologically characterized by the cessation of new leaf development approximately 30 days after germination (DAG). We wondered why this phenomenon appeared in the middle of growth and studied the relationship between Capsicum hybrid weakness and the juvenile‐to‐adult (JA) phase transition. Traits that changed during the early vegetative phase in both parents were the petiole/leaf length ratio, number of leaf lateral veins and stomata, colour of epidermal cells in leaves stained with toluidine blue and expression of miR156 and miR172. Based on the changes observed during the early vegetative phase, C. annuum and C. chinense were transferred to the adult phase 28 DAG. However, the F1 hybrids did not show characteristics of the adult phase at any time point. Furthermore, the phenotypes of hybrid weakness were observed at approximately 35 DAG, when F1 hybrids were presumed to reach the JA transition phase. It has been suggested that the JA transition is involved in Capsicum hybrid weakness.