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.

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Nine stem nematode [Ditylenchus dipsaci (Kühn) Filipjev] isolates were collected from different nematodeinfested regions of the United States and Canada. They were tested for variations in pathogenicity at 15, 20, and 25 C on ‘Ranger’ and ‘Moapa’ (susceptible and ‘Lahontan’ and ‘Caliverde 65’ (resistant) alfalfa (Medicago sativa L.) to determine if variations in plant responses to different nematode isolates should be considered when breeding for resistance to stem nematode. All isolates were generally capable of parasitizing alfalfa; however, a difference in virulence was detected among isolates. Isolates did not demonstrate an interaction with temperature or with alfalfa cultivars. We concluded that a resistant alfalfa developed in a breeding program using one pathogenic isolate would probably be resistant to stem nematode isolates from other regions.

An improved laborsaving technique for evaluating stem‐nematode [Ditylenchus dipsaci (Kühn) Filipjev] resistance in alfalfa (Medicago sativa L.) was developed. To demonstrate the technique, seedlings of three resistant and three susceptible varieties were inoculated by watering with nematode suspensions at seeding and again at 2, 4, and 6 weeks and were rated 16 weeks after seeding. Resistant varieties ‘Apalachee,’ ‘Lahontan,’ and ‘Washoe’ averaged 90.1, 67.8, and 63.7% resistant plants, respectively. Susceptible varieties ‘Saranac,’ ‘Vernal,’ and ‘Ranger’ averaged 34.9, 15.1, and 12.2% resistant plants. Because of its ease of application and its ability to differentiate clearly between resistant and susceptible varieties, this method should appeal to many workers.