Fruit and Tissue Responses of 'Arauco' Olive Fruits to Crop Load in Arid Argentina

Abstract

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 crop loads most often reduce both fruit size and the mesocarp-to-endocarp ratio and delay fruit maturity. Less is known quantitatively, however, about the relationships between olive fruit size and source:sink ratios. Thus, the objectives of the present study were to assess the responses of fruit size and tissue parameters to crop load and to obtain source:sink relationships for these parameters. Fruit samples were taken from low, medium, and high crop load treatments in a commercial orchard (cultivar "Arauco") located in Bañado de los Pantanos, Argentina, at harvest for green table olives in March 2009. Fruit fresh and dry weight, mesocarp weight, and mesocarp-to-endocarp ratio were at least 35% less in trees with high crop load than those with low crop load. The endocarp showed less response with only a modest reduction of 15%. At the cellular level, mesocarp cell number decreased with increasing crop load, while cell size was not affected. Additionally, a bilinear relationship was found between individual fruit dry weight and the source:sink ratio (canopy volume:fruit dry weight) with fruit weight increasing linearly up to a threshold of about 0.8 m3 of canopy volume per kg of fruit dry weight, above which no further increase occurred. Similar relationships were also obtained for mesocarp and endocarp dry weights versus source:sink ratio. These results provide original quantitative estimates of olive source:sink relationships and indicate the close integration between fruit developmental processes and whole tree phenomena.