Development of Next-Generation SuperSour rootstocks with tolerance to HLB

Development of Next-Generation SuperSour rootstocks with tolerance to HLB

Report Date: 02/15/2023
Project: 21-008   Year: 2023
Category: Plant Improvement
Author: Kim Bowman
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them:
Objective 1. Collect field performance data from replicated rootstock field trials and release new rootstock cultivars as justified by superior performance in multiyear field trials.

Collect field performance data. Thirty-one USDA replicated rootstock trials are active, and during this quarter, canopy health data was collected from all trees in the trials. For the trials with Hamlin and lemon scion, fruit yield and fruit quality data was collection during this quarter. Preparations began for the collection of yield and fruit quality data from trials with Valencia scions, which will be completed during the next quarter.

During this quarter, seedlings of the most promising advanced rootstock selections were grown for assessment of trueness-to- type or uniformity from seed, and will be evaluated by morphology and molecular markers.

Preparation for release. The most promising USDA rootstock selections are provided to the FDACS-DPI program for shoot tip grafting and disease testing. Those that have completed the process are held as trees at FDACS and USDA, Ft. Pierce, for use as seed trees and sources of clean budwood. Two new USDA rootstocks tentatively planned for release in 2023 have already gone through the FDACS program, and are available as clean budwood.

Release of new rootstocks. New rootstocks will be officially released by USDA for commercial use when justified by multi-year performance in the early-stage replicated field trials. Based on outstanding performance in field trials, the proposed release documentation has been submitted for two new USDA rootstocks, coded as US-1688 and US-1709. It is anticipated that these two rootstocks will be released during 2023.

Objective 2. Create hybrid rootstocks that 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.

Create hybrids. Selected new crosses are planned for spring 2023, with parental combinations based on new information and breeding values of particular clones assembled over the past year.

Propagate hybrids. New hybrids to be used in trials will be propagated by uniform nucellar seed or stem cuttings. Trees were budded in the nursery with two new superior scion cultivars on 20 rootstocks, in preparation for field planting in 2023. Plant material was prepared in the nursery for one new Stage 2 trial with Valencia scion including the important commercially available rootstocks and the most promising of the new rootstocks. It is anticipated that these trees will be ready for field planting in spring 2024.

Establish replicated field trials. No new field trials were planted this quarter, but tree preparation continued for two trials to be planted in summer 2023.

Tree care in trials. Periodic care was applied in the 31 field trials to maintain tree health and productivity, and manage weeds.

2. Please state what work is anticipated for next quarter:

For the coming quarter, work will focus on making new crosses, cropping data collection from Valencia field trials, continuing propagation of trees for future trials, and care of existing trees in trials.

3. Please state budget status (underspend or overspend, and why):

Budget is on schedule to be spent out by the end of the first year. The project is fully staffed, and work is progressing as planned.

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