Excellent progress was made under this project to develop promising new citrus rootstocks, and three new SuperSour rootstocks are scheduled for release during 2018.� Among the rootstocks currently available for commercial use in large quantities, our previously released rootstock US-942 continues as consistently the overall best performer in field trials.� Other rootstocks recently released, including US-1516, appear promising, but nursery material and field performance data is still limited.� Field data is being collected from numerous established USDA rootstock field trials, to help determine which of a large group of SuperSour hybrid rootstock selections will best provide outstanding tree performance in the face of HLB for the major citrus producing areas of Florida.� Results from existing replicated field trials suggest that some of the new USDA SuperSour hybrid rootstocks can be expected to make sweet orange trees that produce more than twice as much good quality fruit as trees on standard sour orange or Swingle rootstocks.� Additional rootstock field trials to be planted in 2018, as well as focused rootstock development work under a new NIFA-SCRI grant, will further expand the new information that can help Florida growers make good rootstock choices in the future.� Numerous presentations by Dr. Bowman to Florida citrus growers during 2015-18 have helped to transmit updated knowledge about relative rootstock performance, information about new rootstocks under development, and future plans to growers.The overall goal of the project was to develop and release new hybrid rootstocks with outstanding field performance and field tolerance to HLB.� The specific objectives with major accomplishments were as follows:Objective 1.� Collect tree health, size, yield, and fruit quality data from existing rootstock trials.� Rootstock trials established prior to the initiation of this project were the focus of field trial data collection during 2015-2018.� Eight field trials planted between 2011 and 2014 received special emphasis for performance information that was collected, and contained standard rootstocks as well as new SuperSour hybrids.� Summaries of information from several of these trials were presented at grower meetings and field days, and are being prepared for publication.Objective 2.� Test and select the most promising new rootstocks from SuperSour and other progeny groups based on laboratory studies, greenhouse testing, and short term field evaluations.� As indicated in previous reports, work conducted under this objective was minimized at the direction of CRDF at the time the grant was awarded.� Resources that would have been devoted to this objective were re-allocated to the other four objectives instead.Objective 3.� Propagate trees and plant additional rootstock field trials.� Nine new replicated rootstock field trials were field planted from 2015-18 with trees propagated in the USDA rootstock breeding nursery in Ft. Pierce. Trees for eight additional field trials are growing in the USDA rootstock breeding nursery, and will be planted 2018-19.� These trials include standard rootstocks, as well as many new SuperSour hybrid rootstocks.Objective 4.� Release new rootstock cultivars.� The rootstock US-1516 was released in 2015, based on outstanding field performance with HLB.� The three rootstocks US SuperSour 1, US SuperSour 2, and US SuperSour 3 are being released in 2018, based on outstanding field performance with HLB.� Objective 5.� Present information about new and existing rootstocks to Florida growers at meetings and field days, and through grower-targeted and extension publications.� Dr. Bowman made presentations to large groups of Florida growers during at least 14 different shows, meetings, or field days from 2016-18.� Dr. Bowman distributed summary information about field performance of new rootstocks to large groups of Florida growers in at least five separate emails. Dr. Bowman authored four separate refereed publications from 2015-18, presenting detailed performance information on new rootstocks in multiyear replicated field trials.� Dr. Bowman was a co-author of the Florida Citrus Rootstock Selection Guide, 3rd edition, EDIS publication SP248/HS1260.���