Seed, sugar and acid characteristics of 'Zaomi' Ponkan (Citrus reticulata Blanco), a spontaneous mutant of 'Xinnu'

- 'Zaomi' Ponkan is a bud sport mutation of 'Xinnu', showing better fruit quality.
- 'Zaomi' Ponkan is characterized by higher sucrose content in fruit.
- Partial male sterility and self-compatibility cause few or no seed in 'Zaomi' fruit.
- Natural pollination promotes fruit quality of 'Zaomi' Ponkan.

Ponkan is one of the two easy-peeling mandarins grown in China, and 'Xinnu' Ponkan (Citrus reticulata Blanco) is a major cultivar in the industry. We selected a spontaneous mutant of 'Xinnu' named 'Zaomi' Ponkan. Compared to the wild type, 'Zaomi' Ponkan exhibited alternating agronomic traits comprising earlier colouring, thinner peel, fewer seeds and higher sugar content. Pollen analysis showed that 'Zaomi' produced a greater number of deformed, nonviable pollen grains. Experiments in self- and cross-pollination suggested that self-incompatibility of 'Zaomi' contributes to the seedlessness of 'Zaomi' × 'Zaomi'. Fruit quality analysis demonstrated that 'Zaomi' was a high-sugar mutant that was not affected by pollinating combination. This study on the fruit characteristics of 'Zaomi' indicates that partial male sterility and self-incompatibility contributes to fewer or no seeds; natural pollination promotes the overall fruit quality of 'Zaomi' Ponkan. These results provide an explanation of the seed formation of 'Zaomi' Ponkan and supply information relevant to its commercial planting.