Citrus rootstock usage, characteristics, and selection in the Florida Indian River region

Sour orange (Citrus aurantium) has been the dominant citrus rootstock in the Indian River region of Florida since the initial plantings in the 1880s. Use of this rootstock in new plantings has been rare since 1990 because of heightened concern about decline strains of citrus tristeza virus (CTV), to which this rootstock is highly susceptible. Because the proportion of trees remaining on sour orange rootstock and the rate of decline among them are important in predicting the economic consequences for the Indian River citrus industry, two surveys of rootstock usage were conducted for citrus in this growing region. In the first survey, growers were asked about rootstock usage and problems observed across all types of citrus, and responses represented 35% of acreage. In the second survey, growers were restricted to rootstock usage and grower observations on decline for grapefruit (C. paradisi), and responses represented 53% of acreage. Even though 44% of all current Indian River grove area has been planted since 1987, when use of sour orange for new plantings largely ceased, 48% of all citrus and 55% of all grapefruit grove area are currently on sour orange rootstock. The percentage of grapefruit trees on sour orange rootstock that showed significantly health decline in 2000 was 8% based on grower reports. The other rootstocks representing substantial commercial grove area have known problems and limitations that are likely to prevent any of them from gaining the prominence once held by sour orange. Swingle citrumelo (C. paradisi x Poncirus trifoliata) at about 25% of grove area, Cleopatra mandarin (Citrus reticulata) at about 8%, and Smooth Flat Seville (Citrus hybrid) at about 3% all represented similar acreage for grapefruit and across all cultivars, while Carrizo citrange (C. sinensis X P. trifoliata) use was reported for 4% of grapefruit and 13% overall. Evaluation and development of new rootstocks is vitally important for the Indian River area, especially for soils with significant clay and calcium content.