Genetic analysis of flower opening and closing times in hybrids of Iris dichotoma and I. domestica via mixed major gene plus polygene inheritance model

The time of flower opening and closure within a day is not only an important factor for speciation but also strongly influences pollination success, cultivation and attractiveness value. Although the physiological mechanisms behind specific flower opening times of different species within a day are well studied, the genetic mechanism of their flowering processes remains poorly understood due to a lack of suitable materials. Additionally, most studies have focused on traits at specific developmental stages, often overlooking the possibility that different genes may control these traits at various stages. Iris domestica, which blooms in the morning, and I. dichotoma which blooms in the afternoon, are ideal materials for studying the time of flower opening and closing. In this study, we established four generations derived from I. dichotoma and I. domestica, and investigated 9 stages of the opening and closing processes four times, analyzed their variation in flower opening and closing times and explored their genetic mechanism using the major gene plus polygene inheritance analysis model. The analysis revealed significant genetic variation in the opening and closing times. The F₁ generation exhibited intermediate traits between the two parents. The F₂ population displayed high variability, indicating transgressive segregation, with opening times ranging from 7:20:04 to 18:51:42 and closing times from 17:50:47 to 00:24:29. Although the genetic models for the same stage varied across dates, most stages of the opening and closing times were best described by a mixed model involving two major genes and polygenes (E-1 to E-5). In most stages, both major genes and polygenes exhibited additive effects. However, genetic effects varied across stages and dates. The phenotypic variation across the four surveys showed similar trends. Major genes heritabilities ranged from 61.07 % to 98.47 %, while polygenes heritabilities ranged from 0.41 %-38.15 %. These results suggest that flowering time might be influenced by the environment, with diverse genes that were involved in the regulation of flowering processes, and that the regulated genes changed during flowering. These findings lay the foundation for future studies on the genetic mechanism of the flowering time.