CONICET | Buscador de Institutos y Recursos Humanos

Fruit size at harvest is an important parameter of table olive yield and quality, and is a function of the growth of both major tissues, the fleshy mesocarp (pulp) and the endocarp (pit). High fruit loads reduce both fruit size and the mesocarp-to-endocarp ratio and delay fruit maturity. Less is known, however, about the cellular aspects of olive fruit size and potential implications for source:sink relationships. Thus, the objectives of the present study were to assess the responses of fruit size and tissue and cellular parameters to fruit load and to obtain source:sink relationships for these parameters. Fruit samples were taken from low, medium, and high fruit-load treatments in a commercial orchard (cv. 'Arauco') located in Bañado de los Pantanos, Argentina, at the final harvest for green table olives in March 2009. Fruit fresh and dry weight, mesocarp weight, and mesocarp-to-endocarp ratio were approximately 40% less in trees with high fruit load than those with low fruit load. The endocarp showed less response with only a 15% difference. At the cellular level, mesocarp cell number decreased with increasing fruit load, while cell size was not affected. Additionally, a bi-linear relationship was found between mesocarp cell number and source: sink ratio (canopy volume: fruit dry weight) with cell number increasing linearly up to a threshold of about 0.9 m3 of canopy volume per kg of fruit dry mass, above which no further increase occurred. Similar relationships were also obtained for mesocarp dry weight as well as individual fruit and endocarp dry weight versus source: sink. These results provide original quantitative estimates of olive source: sink relationships and indicate the close integration between fruit developmental processes and whole tree phenomena.

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