Location: Genetic Improvement for Fruits & Vegetables Laboratory
2021 Annual Report
Objectives
Objective 1: Generate once-fruiting strawberry selections and varieties for the Mid-Atlantic and surrounding region, for use in traditional matted-row and/or annual plasticulture production systems, with emphasis on high yield; excellent fruit quality; long shelf life; and resistance to Colletotrichum, Botrytis, and foliar and fruit-rot diseases. [NP301, C1, PS1A, PS1B]
Objective 2: Generate repeat-fruiting strawberry breeding selections with an open plant architecture; adequate runner production; high continuous yield; large fruit with excellent quality; and resistance to Colletotrichum, Botrytis, and foliar and fruit-rot diseases for use in developing varieties for extended-season production systems. [NP301, C1, PS1A, PS1B]
Objective 3: Dissect the molecular, genetic, and environmental factors affecting strawberry production-efficiency traits, especially disease resistance and control of plant architecture, through initiation and development of plant organs such as stolons, branch crowns, and inflorescence structures. [NP301, C3, PS3A]
Objective 4: Identify or generate new strawberry mutant genetic stocks for determining the functions or regulation of genes affecting disease resistance. [NP301, C3, PS3A]
Approach
Standard plant breeding methods will be used to generate superior strawberry cultivars for traditional production practices and fruiting for the traditional short spring season. Novel evaluation practices for fruit quality and flavor will be developed and incorporated into the annual breeding cycle. A seedling screen for resistance to anthracnose crown rot, an emerging disease of worldwide importance, will be developed to identify resistant strawberry plants and increase the breeding population’s average resistance to the disease. New cultivars resulting from selection based on increased disease resistance, fruit quality, yield, and shelf life will be released. To help satisfy demand for year-round availability, similar methods will be used to generate improved strawberry plants that fruit for an extended season from April through December. Because the longer-fruiting plants will face weather and pest challenges that are not problems during the traditional fruiting season, new comparison methods will be developed to facilitate identification of plants that produce fruit within the traditional season, and produce equally well outside the traditional strawberry season. Additional research will be done to optimize the season-extending “low-tunnel” production system developed in the previous Project Plan to better evaluate advanced breeding selections. Inheritance of the strawberry’s capacity for continuous fruiting will be studied with both classical and molecular genetics. Characterization of novel mutant diploid lines with microscopy, hormone physiology and analysis, genetics, and genomics will illuminate genetic control and regulation of stolon production, a trait of vital importance to strawberry nurseries and growers.
Progress Report
In support of Objective 1, the development of cultivars for the traditional fruiting season, postharvest evaluation, suspended in Spring 2020 for the COVID-19 pandemic, has resumed in Spring 2021. A release notice for ‘Cordial’ was approved, a patent application for ‘Cordial’ was submitted to the US patent office, and a manuscript was submitted describing ‘Cordial’. Two nurseries received three runner plants of ‘Cordial’ through MTAs. Additional nurseries have become licensed to sell ‘Keepsake’. A breeding selection was identified in Fall 2020 that appears to be highly resistant or immune to powdery mildew. Using only leaves, a collaborator at the University of Maryland will test the level of resistance under controlled conditions. The results will determine if an agreement is needed for further collaborative research. An emerging disease has become endemic in our evaluation fields. Colletotrichum siamense in the C. gloeosporioides species complex was identified by sequencing by a University of Maryland collaborator. In Fall 2020, it affected the seedling field. It appears the breeding population caries genes for resistance to crown death caused by this species. In Spring 2021, the disease affected the project’s replicated yield trials. All Beltsville cultivars were resistant, but several selections succumbed to plant death. All cultivars resistant to anthracnose fruit rot caused by C. accutatum are susceptible to anthracnose fruit rot caused by an unknown Colletotrichum being sequenced by a UMD collaborator. Genotypic differences in the percentage of affected fruits, observed after the disease expressed on 1 June 2021, will be the basis of the coming crossing plan.
In support of Objective 2, the development of repeat-fruiting strawberry cultivars, the project entered a new stage. Previously, we evaluated single observation plots to plan crosses; now, breeding selections are compared with reference cultivars to identify new potential cultivars superior to those currently available. In Summer 2020, three breeding selections were compared with three reference cultivars in replicated evaluations. One of the selections, B2897RB, had double the yield of the current leading cultivar and a much better flavor. An PE MTRA was developed to transfer plants of B2897RB to Just Greens DBA “AeroFarms” for evaluation in indoor production. In Spring 2021, 16 additional repeat-fruiting breeding selections were planted with two reference cultivars in replicated evaluations.
In support of Objective 3, dissection of molecular, genetic, and environmental factors affecting strawberry production-efficiency traits, two separate populations were planted and scored to determine that the previously characterized mutant phenotypes involving fruit shape and inflorescence length are the result of single recessive gene mutations. Tissue was collected and stored for bulk segregant sequencing analysis to determine the mutated gene in each case.
In support of Objective 3, dissection of molecular, genetic, and environmental factors affecting strawberry production-efficiency traits, bulk segregant sequence data was analyzed using VARMAP to predict that the non-runnering mutant, nr1, resulted from a SNP in a gene encoding a histone methyltransferase is homologous to a meristem defining gene in Arabidopsis. Crosses were made to determine how this gene affects the expression of two previously identified gibberellin signaling genes, and seeds are being produced.
In support of Objective 3, dissection of molecular, genetic, and environmental factors affecting strawberry production-efficiency traits, an inbred line of diploid Fragaria vesca ssp. bracteata was developed as a tool for identifying genes for important traits that will be useful for improvement of the commercial octoploid strawberry. Fragaria vesca ssp. bracteata was recently identified as being more likely to have contributed to the genome of the commercial strawberry than Fragaria vesca ssp. vesca. The new inbred line was shown to regenerate readily from tissue culture and is being analyzed for ease of transformation with Agrobacterium tumefaciens for gene editing to test gene function.
Accomplishments
