1a. Objectives (from AD-416):
1. Improve temperate stone and pome fruit quality traits. 2. Improve host-plant resistance of temperate stone and pome fruit to plum pox virus, tomato ringspot virus, prunus necrotic virus, and prune dwarf virus. 3. Develop a model biotechnology risk mitigation system and efficient genetic transformation protocols for Rosaceae. PDRAM #R08 Program Increase Objective: 4. Initiate a FasTrack breeding project to develop, characterize, and select early and continual fruiting lines of plum, pear, and apple, and relevant rootstocks to accelerate fruit breeding programs.
1b. Approach (from AD-416):
This project proposes the development of genetic solutions to the major problems affecting temperate tree fruit production and consumer acceptance of tree fruits through a coordinated effort utilizing the most appropriate technologies. The improvement of fruit quality will be approached through traditional breeding of novel genetic material, and also through the isolation and transgenic manipulation of key genes that control fruit development, stone formation, and ripening. The use of these diverse technologies will be coordinated in order to develop tree fruit varieties with improved flavor and firmness that is maintained post-harvest and investigate the possibility of creating marketable stoneless varieties. Improvement of fire blight resistance in pear will be approached through hybridization of existing fire blight resistant germplasm to develop new resistant cultivars that have high fruit quality. Pathogen- and host-derived resistance to stone fruit viruses will be incorporated into commercial quality cultivars through genetic transformation. Improved tree form for high-density production systems in peach will be approached through hybridization of peach germplasm with desirable tree growth habits such as columnar and semi-columnar with the aid of molecular markers that improve breeding efficiency. Pear growth habits will be manipulated through genetic transformation. Foundational work in genetic engineering and risk mitigation will facilitate the development of enhanced technologies that will help alleviate industry concerns over marketing genetically engineered crops. Improved plant material generated from both the laboratory and field will be evaluated in collaboration with the industry and consumer groups to facilitate its utilization.
3. Progress Report:
Towards the goal of developing stoneless plums, expressed RNA was sequenced (5-30 million sequences from each sample) from a series of fruit collected during the time of endocarp (Stone forming tissue) determination in both normal stone plum fruit and 'Stoneless' mutant plum fruit. The populations of RNA were compared to known peach genes and candidate genes identified that were expressed differently between the two phenotypes. The peach breeding program has produced selections with high sugar content, favored by consumers, and upright growth habit, a promising trait for growers. These selections have been transferred to the CRADA partner for distribution to the network of grower-testers for evaluation. To develop disease and insect resistant pears, seedlings and selections were evaluated for fruit quality and resistance to fire blight, Fabraea leaf spot, and pear psylla. Crosses were made to introduce improved storage and shelf life, as well as texture, and to study the inheritance of these traits. Selections of pear have been made based on resistance to pear psylla and fruit quality. To find genes of interest for fruit quality traits and disease resistance, 'Improved French' plum, multiple seedlings of peach, and six apricots were whole genome sequenced. Utilizing gene silencing as an alternative gene containment strategy has been extensively analyzed in plants using genes critical for meiosis. The silencing of all chosen three genes gave rise to a male sterile phenotype without compromising vegetative growth. Three promoters specific for floral meristem have been characterized in transgenic plants and all promoters analyzed confer apical meristem-specific expression during transition from vegetative to reproductive growth. These promoters have been incorporated into TRECS for improvement of gene excision efficiency, and characterization of these transgenic plants for gene excision efficiency is in progress. The 'FasTrack' breeding system has been used to rapidly develop the second generation of plums integrating Plum pox virus (PPV) resistance from 'HoneySweet' plum into the genetic background of California-adapted plums. Molecular markers have been developed that distinguish the genetic background of 'HoneySweet' (PPV resistant) and 'French' (California-adapted plum variety) to aid in selecting progeny with the optimum combination of traits required by the California industry and with PPV resistance. Cultural systems to improve early flowering plum tree growth, fruit production, and seed germination have been developed. Two pear rootstock cultivars, 'OHF 87' and 'OHF 97' were transformed with a gene to determine if reduced active gibberellin will result in rootstocks with a dwarfing effect on scions.
1. Identification of a gene that controls branch angle in trees. Growers have many choices of fruit varieties but few choices in tree growth habit. In order to maximize productivity and fruit quality, the currently available tree forms require intensive management through pruning and other forms of training. Tree pruning and training are major costs of production. These added costs could be substantially reduced if it were possible to genetically manipulate tree architecture to produce more desirable growth forms. ARS researchers at Kearneysville, West Virginia, identified a gene that controls branch angle in peach trees and most other plant species. Knocking out the gene leads to an upright or columnar growth form that can be planted at higher densities. These findings will enable the creation of trees with desirable branch angles both through genetic engineering and breeding. The availability of new columnar-type tree architectures will positively impact numerous fruit, nut, and other tree-based industries by facilitating high density planting and other training systems that improve productivity and/or reduce labor costs.
Zagrai, L., Ravelonandro, M., Gaboreanu, I., Ferencz, B., Scorza, R., Zagrai, L., Pamfil, D., Popescu, O., Kelemen, B. 2011. Field plot assessments demonstrate that transgenic plums expressing Plum pox virus (PPV) coat protein gene do not affect the PPV strain composition or produce PPV recombinants. Journal of Plant Pathology. 93(1):159-165.