Good progress was made in continuing the development of new hybrid rootstocks for the Florida citrus industry. As requested by CRDF, highest priority is being placed on work to develop hybrid rootstocks that can be made available for release to growers in the next four years, including about 300 Supersour-type rootstock selections. It is expected that at least one of these rootstocks will be released within two years, with more to be released in the following years as further information is collected from ongoing field trials. During this quarter, one new replicated rootstock field trial was planted on a central ridge site. The trial used Hamlin scion and included 8 replicates of 50 different rootstocks. Standard rootstocks included for comparison were Sour orange, Swingle, Cleopatra, and Ridge. Emphasis in the new trial was on SuperSour selections for which preliminary performance information is promising and that are in the DPI clean source program. Trees in the nursery were in the final stages of preparation for planting three additional field trials in the coming quarter. The trials will each include 8-12 replicates of about 50 new rootstocks, along with several standard rootstocks for comparison. Emphasis in these new trials is also on SuperSour selections for which other performance information is promising and that are in the DPI clean source program. Liners were prepared in the nursery by seedage and cuttings for additional field trials to be prepared for future plantings, based on new hybrid rootstock selections that look the best with HLB in preliminary field sites. Additional seed source trees were prepared for field planting, so that more seed will be available from the SuperSour rootstocks for commercial use after release. Research was conducted in collaboration with commercial nurseries and tissue culture propagation facilities to study and compare rootstock liners produced from seed, cuttings, and micropropagation. The trend for rapid expansion in the use of new rootstocks following release makes it clear that available seed will frequently be inadequate to satisfy commercial demands for the newest rootstocks. It is likely that cuttings and micropropagation of rootstocks will become increasing common. Noted differences in nursery performance of liners by propagation type, have prompted concerns about the influence of propagation type on field performance. We have initiated research to study these issues and address the concerns in a constructive way. Analysis of results from previously established trials indicates that HLB introduces additional variability to trials that requires more than the previously effective five or six statistical replicates to provide clear evidence of rootstock performance. Based on this observation, new USDA rootstock trials will usually include more than six statistical replications, regardless of the number of trees per replication. Using valid statistical comparisons is essential to develop reliable information about relative rootstock performance in field trials and should be the foundation of grower rootstock selection for new field plantings. I am working with the UF breeding team under two HLB-MAC projects to establish at least 13 additional rootstock field trials over the next 12 months, combining the best advanced new rootstocks from the USDA and UF breeding programs. The first six of these trials are expected to be field planted with grower-cooperators in the next quarter. Additional information is available on the USDA rootstock breeding project, on request.