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United States Department of Agriculture

Agricultural Research Service

Research Project: USDA-ARS Citrus Breeding Trust with New Varieties Development and Management Corporation

Location: Subtropical Insects and Horticulture Research

2013 Annual Report


1a.Objectives (from AD-416):
To develop high quality new cultivars of priority fresh citrus market categories.


1b.Approach (from AD-416):
Use conventional hybridization of priority parents, and irradiation of seedy priority selections, with all parents and treated plant material identified in consultation with the NVDMC board. Each year a plan for developing and testing material will be explicitly developed. NVDMC will provide funding for two technicians to greatly accelerate the process and will facilitate testing of material by coordinating plantings in growers' farms.


3.Progress Report:

This project is related to Objective 1: Create new genetic combinations of citrus, Objective 2: Screen germplasm for important traits and select superior individuals, Sub objective 1 D: Create new scions and rootstocks with potential resistance to huanglongbing (HLB) and citrus bacterial canker (CBC) by genetic transformation.

New hybridizations: A majority of the 2013 crosses focused on seedless selections and huanglongbing (HLB) resistance/tolerance. 1408 flowers were used from 86 parental combinations. Kishu was used as a pollen parent in crosses with 7 advanced ARS numbered selections displaying excellent fruit quality and/or good fruit quality and HLB tolerance and one HLB-tolerant cultivar (‘Bower’). One identified seedless Kishu hybrid was also used as a pollen parent. W. Murcott was used as a pollen parent in crosses with 7 advanced ARS numbered selections displaying excellent fruit quality and/or good fruit quality and HLB tolerance. Many crosses were made using identified sources of HLB tolerance and resistance to pyramid HLB tolerance/resistance with good fruit quality. Some crosses made using best Ponkan selections with half pummelo/half mandarin selections of good quality and HLB tolerance. Ponkan has been identified as pollen parent of sweet orange and effort is intended to resynthesize HLB tolerant sweet orange.

New selections: Ten new high quality scion types were identified. Several appear suitable for cultivar release following irradiation to reduce seediness and several seem to have a high degree of HLB-tolerance or resistance. All selections are treated with antibiotics and budded into the greenhouse.

Screenhouse for trellis: A screenhouse has been completed for the trellis to train seedlings and encourage early flowering. A low-seeded easy peeling Tankan (discussed with the industry as a possible “easy-peeling Florida orange”) identified from a seedling planted at Picos Farm, was rescued as seed, and has been budded onto the trellis trees. Several genotypes have been budded in a replicated trial of juvenility-reduction components. All trees in the trellis house will have superb cold-protection and should remain free of huanglongbing and citrus tristeza virus, permitting rapid entry into second tests.

Screenhouse for breeding parents: A one acre screenhouse to contain breeding parents at Leesburg was designed and half of the costs covered by the Florida Citrus Research Foundation and half by the Citrus Research and Development Foundation. It is now completed. Large parent plants will be placed in the ground within the screenhouse to permit production of numerous flowers and fruit without threat of cold-injury or huanglongbing.

Progress with budwood cleanup: Twenty-two priority selections have been shoot-tip grafted to eliminate pathogens. An experiment was conducted to compare techniques for rescue of huanglongbing infected budwood.

Characterization of germplasm: We submitted juice samples of several promising new orange hybrids for volatiles testing by the Citrus and Subtropical products unit to determine whether they may be suitable for official recognition as sweet oranges. They were found to be very similar to sweet orange and a draft publication is underway.

It has become apparent that many conventional citrus types have considerable resistance or tolerance to huanglongbing. In a replicated field trial at Picos Farm, tree health and productivity of ‘Triumph’, Jackson’, and standard cultivars ‘Marsh’ and ‘Flame’ were assessed for 3 years. Cumulative numbers of fruit/tree were greater for ‘Triumph’ & ‘Jackson’ (255/220) than for ‘Flame’ & ‘Marsh’ (29/66). Cumulative percent fruit drop was greater in ‘Flame’ & ‘Marsh’ than ‘Triumph’ & ‘Jackson’ Fruit quality assessments were made each cropping season. ‘Triumph’ & ‘Jackson’ fruit met commercial maturity standards whereas ‘Flame’ & ‘Marsh’ fruit did not due to low Brix/acid ratios. In 2011/2012 many ‘Flame’ & ‘Marsh’ were small and/or misshapen while ‘Triumph’ & ‘Jackson’ fruit were of normal size and shape. These results suggest that ‘Triumph’ & ‘Jackson’ or other grapefruit-like cultivars may be viable alternatives to standard grapefruit cultivars in the presence of severe canker and huanglongbing. This work was published in the last year.


Last Modified: 11/22/2014
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