Performing rootstocks: A difficult choice for the nurserymen - sharing a 40 years experience

Modern citriculture is based on composite grafted individuals. By this technique the nurserymen are able to secure a homogenous trueness-to-type of the scion cultivar, and address correctly the biotic and abiotic constraints of the rootstock part. Over the last dozen years, scores of novel rootstocks were proposed to solve various problems such as #Phytophthora# root rot and gummosis, Tristeza, Blight, or to obtain individuals more tolerant to drought, alkalinity and salinity. Moreover a proper rootstock screening may have clear advantages on important aspects such as early bearing through the reduction of juvenility, average yield per canopy volume, or even fruit quality (SSC, juice content). So far rootstock multiplication in nurseries has been carried out by seedling, and this requires special attention in the management of seed production for securing large amounts of nucellar progenies. Not only the seed production of a given rootstock cultivar is important but also its percentage of seed polyembryonic. This paper is presenting the results of about 40 years of rootstock evaluation conducted at the station of San Giuliano, Corsica, since 1958. The characteristics of twenty different rootstock cultivars ranging from #Poncirus# and its hybrids, sour orange, Gou Tou, Cleopatra mandarin, Rangpur lime, to Yuzu are presented from the point of view of nursery management, i.e. seed production, rearing and grafting of the seedlings, thorniness, scion/rootstock compatibility. Long-term field evaluation (over 15 to 30 years) of these rootstocks is presented mainly with clementine as scion cultivar. This approach enabled to find the best possible combinations in our Mediterranean pedo-climatic conditions and collect basic information useful for citrus nurserymen. All this information must be taken into account by the nurserymen planning their rootstock screening, and willing to improve the treatment and storage of their seeds for meeting the grower's demand. (Résumé d'auteur)