New Citrus Rootstocks Released by USDA 2001-2010: Field Performance and Nursery Characteristics

Four new citrus rootstocks developed by USDA, ARS and released between 2001 and 2010 have gained considerable commercial popularity in Florida and have been used for propagation of more than 2 million trees over the last 2 years. Results from three new field trials are presented comparing these rootstocks with other important rootstocks, and discussion is presented to summarize field performance in these trials and from numerous other sources. The rootstocks vary widely in their effect on tree vigor. When used as a rootstock for sweet orange, 'US-802' typically supports strong vigor and development of a large tree, 'US-812' and 'US-942' provide moderate vigor, and 'US-897' induces a relatively dwarf tree. Other characteristics and attributes of the four rootstocks are also discussed, including effects on cropping, fruit quality, disease and pest resistance, and tolerance of abiotic factors. Of special relevance, relative tolerance of these rootstocks to huanglongbing (HLB) disease can be surmised from a combination of data from several sources, with 'US-942' and 'US-802' typically providing the best yields per tree in trials containing many rootstocks and affected by HLB. 'US-812' and 'US-897' have appeared to have most utility in locations where HLB is not present or effectively managed, or where trees are being planted at high density to optimize production per unit area. To facilitate continuing expansion of commercial use, information on seed production, and the relative ease of nursery propagation is also presented.