The high incidence of psorosis disease prompted the Texas citrus industry to initiate a voluntary virus-free program in 1948, but by the 1960s it was no longer operating. A similar program in the 1980s was short-lived, but the discovery of Citrus tristeza virus in nursery trees in 1992, the continued dominance of sour orange rootstock, and the presence of viroids and viruses which affect alternative rootstocks were catalysts for a mandatory virus-free budwood program. Selected trees of the

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... rcially important varieties of grapefruit and sweet orange were indexed for several viruses and viroids, subjected to shoot tip grafting and re-indexed. These plants provided the start of a foundation block of trees to which other varieties imported from the California Citrus Clonal Protection Program have been added. There are now over 80 varieties in the foundation block and nearly 280,000 buds have been supplied to nurseries since 1998. Since there is no current expansion or replanting of commercial citrus in the Rio Grande Valley of south Texas, a growing proportion of budwood is for the homeowner market, especially in east Texas.