Limited carbohydrate availability as a potential cause of fruit abortion in Rubus chamaemorus

Fruit abortion can be caused by a range of abiotic and biotic factors. To gain a better understanding of the causes of the high fruit abortion frequency in cloudberry (Rubus chamaemorus L.), we manipulated different sources of carbon, that is, leaves and rhizome. We also manipulated flower number to see if competition between floral ramets explained fruit abortion in cloudberry. Reducing the number of flowers had no impact on fruit abortion frequency. In fact, the species forms an extensive rhizome network with only a few ramets per clone and competition between floral ramets is unlikely. Ramet defoliation had limited impact on fruit abortion, but successful fruit development was affected by rhizome length. The longer the rhizome, the higher the chances to mature a fruit. These results suggest that current photoassimilate production by the reproductive ramet alone is insufficient to insure fruit development. Carbon can come from other ramets but distances are usually high between ramets. Fruit production might thus depend on the use of stored carbohydrates in the rhizome to balance insufficient photosynthetic contribution during fruit production.