Acta Horticulturae

The citrus nursery tree certification program in Spain includes four blocks of trees: 1) The protected foundation block, maintained at IVIA, that includes healthy plants of local and foreign varieties recovered by shoot-tip grafting in vitro. Plants are grown in containers inside insect-proof screenhouses. 2) Foundation blocks propagated with budwood from the protected foundation block and also grown inside screenhouses. They belong to individual nurseries or nursery groups. 3) Budwood increase blocks, maintained inside screen-or greenhouses at each nursery, include plants propagated directly from foundation trees to increase the number of buds for propagation of certified trees. 4) Certified nursery trees propagated with budwood from the increase blocks and grown in screen-or greenhouses or in the open field. Plants of each block are periodically indexed for different pathogens according to the regulations. The program started in 1979 when the first healthy plants were released to the nurseries and the first certified plants arrived to growers in 1982. Since then, more than 142 million certified plants of 103 varieties have been propagated, with sweet oranges representing 51%, clementines 28%, other mandarins 14%, lemons 6% and grapefruits 1%. Presently Carrizo citrange is used as rootstock for 59% of the nursery plants and Citrus macrophylla for 19%. A total of 40 nurseries, grouped in 7 foundation blocks, are presently operating. Under this program practically all the Spanish citrus industry has been renewed with healthy plants. Today, traditional graft transmissible pathogens are not a problem for our citrus industry