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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

2012 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 major emphasis of our hybridizations this spring was use of Kishu as a pollen parent to genetically transmit seedlessness to half of the resulting progeny. There were 1029 flowers crossed between the two farms this year. 49 total types of crosses were made. These cover mandarin types, orange types, grapefruit types and some mixed types such as tangelos. The vast majority of the crosses were made to focus on seedless selections and huanglongbing tolerance trying to pursue the fastest conventional path to conventional huanglongbing-resistant cultivars.

New selections: Two new quality mandarin hybrids were identified in Fort Pierce, one with particularly fine-flavor and large size and the other with good quality that ripens late. An excellent complex pummelo - trifoliate hybrid was identified in Fort Pierce that is mono and seems tolerant of huanglongbing which should be an excellent parent for grapefruit types. Two new monoembryonic hybrids were identified that are good tasting, 1/16 trifoliate, possibly huanglongbing resistant, and very much like a sweet orange.

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 will be covered by the Florida Citrus Research Foundation and half by the Citrus Research and Development Foundation. 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 priority mandarin hybrid selections have been shoot-tip grafted to eliminate pathogens. An experiment was conducted to compare techniques for rescue of huanglongbing infected budwood. Vacuum infiltration with antibiotics (penicillin/streptomycin) or the antimicrobial peptide D4E1 doubled the number of resulting plants which were tested as Liberibacter-free (50+%).

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.

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.


Last Modified: 9/29/2014
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