New field performance information is being collected on about 400 new SuperSour-type rootstocks in field trials. Performance attributes being assessed include tree growth, tree health, fruit yield, fruit quality, tolerance of high pH soil, and tolerance or resistance to HLB and other diseases. New rootstocks are only appropriate for large-scale grower use when outstanding performance has been documented by statistically replicated trials over multiple years. It is anticipated that at least one of the best new SuperSour rootstocks will be released for commercial use within 3 years. In the meantime, outstanding performance has been documented for US-802, US-897, and US-942 rootstocks over multiple years in trials affected by HLB, and these rootstocks are available in large numbers through commercial nurseries. During this quarter, trees in field trials were measured for tree size and scored for health, HLB symptoms, and samples were collected from some groups for PCR detection of Las infection. During this quarter, yield and fruit quality data were collected from 3 rootstock field trials with late maturing scion varieties. The most outstanding rootstock in a long-term Valencia trial on a flatwoods site in Collier County was US-802 rootstock, which yielded significantly more fruit than every other rootstock in the trial, including the second highest yielding rootstock, US-942. Every tree in this trial is infected with Las, but trees on US-802 still yield much more fruit than trees on any other rootstock. Analysis was completed on data from several established trials to assess relative rootstock performance, rootstock effects on yield, fruit quality, tree size, and HLB symptom development. A comprehensive presentation on standard and new rootstocks was made at the Florida Citrus Growers Institute. A new paper was prepared, providing a comprehensive comparison of field performance for the new USDA rootstocks with other standard rootstocks, and was submitted for publication. Trees in the USDA nursery on a large number of advanced rootstock selections, especially SuperSour-type, were continued in propagation for field trials to be planted in 2016. Nursery experiments were conducted with promising new rootstocks to determine nursery-related traits important for commercial use. Cooperative work continued with commercial nurseries involved with micropropagation, to facilitate more rapid deployment of the best new rootstocks. A cooperative project has been initiated with Dr. Ute Albrecht (UF, Immolakee) to compare trees on rootstocks propagated by seed, cuttings, and micropropagation, so that growers can have confidence that rootstocks propagated by the different methods will have equivalent performance. Greenhouse experiments continued to assess rootstock tolerance to HLB, CTV, and high pH. Research was initiated to more fully study the HLB-tolerance of trees formed by grafting HLB-susceptible scions on HLB-tolerant rootstocks. A better understanding of this behavior will help to more quickly identify new rootstocks with higher and more reliable levels of HLB tolerance in the field. Cooperative planning continued with UF researchers at several locations, to submit grant proposals to USDA NIFA to help fund expanded rootstock research and development efforts. Cooperative grant-funded work continued with UF researchers to establish acid fruit rootstock trials in South Florida. Cooperative grant-funded work continued with UF researchers and a commercial nursery to propagate trees for use in multiple rootstock field trials sponsored by the HLB MAC program. Trees from the commercial nursery are scheduled to be planted into six cooperative field trials in 2016, and six more field trials in 2017.