1: Improve environmental stress and disease resistance in tree fruit crops. 1.A. Identify and characterize sources of fire blight resistance for use in apple scion breeding programs. 1.B. Characterize expression patterns and sequence differences of select apple drought-responsive genes in Malus sieversii lines exhibiting high and low water use efficiency. 1.C. Utilize transcriptomic and high-throughput genetic screening approaches to identify CBF-regulated and other stress-regulated genes, and characterize their functional role in stress tolerance and dormancy using transgenics and field evaluation. 2: Develop an accelerated breeding system for new tree fruit crops utilizing transgenic early-flowering lines.
Abiotic and biotic stresses play a major role in determining the economic viability of fruit crop production and postharvest quality. A single fire blight epidemic can destroy an entire young orchard and unfavorable environmental conditions, such as freezing temperatures, as well as heat and drought stress can result in significant reductions in yield, quality, and tree longevity. The overall objective of this project is to utilize genomic and molecular approaches to identify genes that convey resistance to abiotic and biotic stress in fruit crops, identify genetic markers for disease and stress resistance that can be utilized by apple breeders in marker-assisted-breeding programs, and to develop a breeding system that will facilitate the incorporation of specific traits, especially from novel genetic resources, such as Malus sieversii, into advanced selections of breeding lines. Quantitative trail loci (QTLs) and molecular markers for fire blight resistance will be developed for resistance derived from Malus sieversii and ‘Splendour’ apple. Targeted genome sequencing of the promoters of select dehydration and water use efficient responsive genes will be applied to lines of xeric-adapted Malus sieversii. Promoter analysis will identify cis-elements known to affect gene expression. Methylation differences between lines during simulated drought will be evaluated to reveal potential targets for gene regulation. The contribution of the CBF (C-repeat binding factor) family members to cold hardiness, dormancy, and growth will be evaluated. An accelerated breeding system for apple will be developed utilizing transgenic early-flowering lines to facilitate rapid integration of important genetic traits from novel apple genotypes into advanced breeding lines. The proposed research will result in the identification of genes, molecular markers, and a breeding system that can be used to efficiently develop apple germplasm with increased resistance to biotic and abiotic stress.
Host plant resistance is one of the most effective and sustainable options for managing fire blight, a devastating disease of apple and pear. 'Splendour' apple, which has excellent flavor and is resistant to fire blight, was found to transmit its resistance to 25% of its progeny and will, therefore, be a useful donor of resistance for apple breeding programs. Since genetic diversity is often lost during crop domestication, accessions of Malus sieversii, the progenitor of the domesticated apple, represent a valuable resource for disease resistance. Two hundred accessions of Malus sieversii from a USDA-ARS collection were selected as potential sources of disease resistance for apple scion breeding. Based upon controlled challenges with the fire blight pathogen in 2013 at both Wenatchee, Washington and Kearneysville, West Virginia, 26 wild Malus sieversii accessions were identified as highly resistant to fire blight (immune) and another 38 were identified as resistant to fire blight (resistance equivalent to 'Delicious'). Differences in expression patterns associated with drought response can be correlated with differences in water use efficiency and/or drought resistance. Simulated drought experiments with three Malus sieversii lines from xeric site six in Kazakhstan have been completed, including 'Royal Gala' as a control line for each experiment. Climate change has resulted in early budbreak in many species of fruit crops making them very susceptible to subsequent freezing events. Therefore, there is a need to develop cultivars or management practices that allow trees to adapt to these changes in climate in order to maintain yields. Transgenic lines of an apple rootstock cultivar, 'M.26', overexpressing a CBF transcription factor from peach have been field tested for three years. The transgenic lines have increased cold hardiness, early fall dormancy, delayed spring budbreak, and reduced growth. A planting of grafted trees has been established to determine if the transgenic rootstock can be used to affect the physiology and phenology of non-transgenic scions. Breeding new apple varieties takes 25-30 years due to its long juvenile phase. Development of an early-flowering apple would greatly increase apple breeding efficiency. A total of 10 transgenic lines expressing two different "early-flowering" genes have been produced in 'Royal Gala'. Characterization of these early flowering lines has been initiated.
Artlip, T.S., Wisniewski, M.E., Norelli, J.L. 2013. Field evaluation of apple overexpressing a peach CBF gene confirms its effect on cold hardiness, dormancy, and growth. Environmental and Experimental Botany. 106:79-86.
Guo, R., Xu, X., Bassett, C.L., Li, X., Zheng, Y., Gao, M., Wang, X. 2013. Genome-wide identification, evolutuionary and expression analysis of aspartic proteases gene superfamily in grape. Biomed Central (BMC) Genomics. 14:554.
Li, J., Hou, H., Li, X., Xiang, J., Yin, X., Gao, H., Zheng, Y., Bassett, C.L., Wang, X. 2013. Genome-wide identification and analysis of the SBP-box family genes in apple (Malus x domestica Borkh). Plant Physiology and Biochemistry. 70:100-114.
Artlip, T.S., Wisniewski, M.E., Bassett, C.L., Norelli, J.L. 2013. CBF gene expression in peach leaf and bark tissues is gated by a circadian clock. Tree Physiology. 33:866-877.
Villanova, L., Wisniewski, M.E., Norelli, J.L., Vinas, I., Torres, R., Usall, J., Phillips, J.G., Droby, S., Teixido, N. 2014. Transcriptomic profiling of apple in response to inoculation with a pathogen (P. expansum) and a non-pathogen (P. digitatum). Plant Molecular Biology Reporter. 32:566-582.
Wisniewski, M.E., Nassuth, A., Teulieres, C., Marque, C., Rowland, L.J., Cao, P., Brown, A. 2014. Genomics of cold hardiness in woody plants. Critical Reviews in Plant Sciences. 33:92-124.