Objective 1. Create hybrid rootstocks which combine germplasm from parental material with good rootstock traits and HLB tolerance, propagate the most promising of these hybrids, and establish replicated field trials with commercial scions.
Hybrid seed from 2018 crosses were grown, including SuperSour type parentage of unique HLB tolerant types, and 51 hybrids were selected for continuing work. Seed source trees were propagated for several new hybrids being prepared for release, and additional trees propagated as a source for cuttings. A study was completed evaluating seed propagation of some of the newest US rootstocks and presented at the FSHS meeting. Information was prepared and distributed to nurseries about accurately identifying many of the new citrus rootstocks.
Multiple budded trees of about 130 selected new rootstock hybrids were grown in the nursery, in preparation for field planting other new rootstock field trials later in 2019. These nursery trees included many of the most promising SuperSour hybrids identified in ongoing trials established in previous years, and several commercial standard rootstocks. These nursery trees also include other new and different hybrids chosen because of newly available information about parentage and characteristics best associated with outstanding traits. Three new field trials with sweet orange scion will be planted from these trees later in 2019, including one trial in the East coast region, one in the Central ridge region, and one in the Southwest region.
Objective 2. Collect field performance data from early-stage replicated rootstock field trials and release new rootstock cultivars as justified by superior performance in multiyear field trials.
Seventeen rootstock trials planted prior to summer 2018 (as described in the Proposal Appendix ii) were monitored and used for data collection on field performance, as appropriate during this quarter for the scion involved. During this quarter, data collection in established trials was focused on tree size and tree health. Plans were made to begin posting results from USDA rootstock field trials to the site www.citrusgreening.org, a webpage sponsored by USDA-NIFA, and that information will be updated at least once per year for each active trial. The first trial summary data for posting to this site has been assembled from a cooperative trial in the Ft. Meade area (Planted 2014, Valencia scion, 24 rootstocks, 7 replicates), and has been modified and provided in suitable format to the host Boyce Thompson Institute.
The three new USDA rootstocks released in November 2018, identified as SS1, SS2, and SS3, are being propagated in nurseries for numerous planned commercial plantings. Additional information is being collected from established trials and other experiments on these newest rootstocks. Made significant contributions to completion of 4th edition of the Florida Citrus Rootstock Selection Guide, the newest revision of the IFAS extension publication.