All fruit no flowers

Fruit and nut farmers across a wide range of crops will be familiar with the phenomenon of alternate bearing – where a tree alternates between a high yield one year and a low yield the next. Growing fruit, which were initiated in the previous season, are able to suppress flowering and therefore reduce the number of fruits in the following season. Only shoots close to the developing fruits are impacted, not the whole branch or tree. The more fruits there are on a tree, the more shoots will be impacted. Sometimes, a particularly high yield of fruit will cause the tree to bear no fruit at all the following year.

‘Nadorcott’ mandarin bearing fruits in the Mediterranean area of Spain. Image courtesy of M. Agustí (Agustí et al. , pp. 376–384).

The image above shows a mandarin tree, which exhibits a high degree of alternate bearing, with a large crop of fruits. Citrus trees were used by Professor Manuel Agustí and colleagues to investigate the molecular mechanism behind this phenomenon.

They found that the presence of fruit caused epigenetic changes that correlated with increased gene expression of a floral repressor. This means that flowering is not initiated even when the environmental conditions are just right. However, newly emerging shoots in the trees bearing fruit showed a different epigenetic pattern associated with repression of the floral repressor. This would allow fruit production to begin once again after the season of low yield.

Read the article: Agustí, M., Mesejo, C., Muñoz‐Fambuena, N., Vera‐Sirera, F., de Lucas, M., Martínez‐Fuentes, A., Reig, C., Iglesias, D.J., Primo‐Millo, E. and Blázquez, M.A. (2020) Fruit‐dependent epigenetic regulation of flowering in Citrus. New Phytologist, 225: 376-384. doi: 10.1111/nph.16044

Freja Kärrman-Bailey
Events and Promotion Coordinator
New Phytologist Trust