Rootstock as a fruit quality factor in citrus and deciduous tree crops

This mini-review provides a definition of fruit quality, a comparison of rootstock effects and importance in deciduous and citrus crops, and a detailed examination of fruit quality in relation to citrus rootstocks. Fruit quality is defined in simple, complex, and specific terms recognising that it is eventually a matter of consumer preference. When fruit quality is measured as physical traits and chemical composition, little rootstock effect has been demonstrated among deciduous crops as compared to citrus rootstocks which have well-known effects on more than 10 quality factors. This difference is explained by comparing the relative importance of rootstocks for precocity, yield, and tree size control, and through contrasts in annual phenological cycles, fruit respiratory behaviour, crop load and canopy management techniques, and the use of clonal rootstocks in citrus and deciduous fruit trees. Mechanisms of rootstock effect on fruit quality are discussed using apple, Malus domestica Borkh. (a climacteric, starch accumulating fruit), and citrus fruit (which are non-climacteric and accumulate soluble solids). An argument is presented that apple quality is determined largely by factors related to crop load and canopy management whereas citrus fruit and juice quality are closely related to rootstock effects on plant water relations as evidenced by field trial results, sucrose transport, and reciprocal fruit grafting studies.