1a. Objectives (from AD-416):
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]
1b. Approach (from AD-416):
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.
3. Progress Report:
The previous in-house Project 8042-21220-254-00D terminated 25 February 2018. Objectives 2, 3, and 4 from the previous project were incorporated into the new in-house Project 8042-21220-257-00D in Objectives 1, 2, and 3. In support of Objective 1, ARS scientists in Beltsville, Maryland, tested replicated plots of breeding selections for yield, percentage fruit rot in the field, fruit quality, brix (sugar content), pH, and shelf life. Measuring brix and pH on every plot at every harvest is a new addition to this project’s data collection. Changes recorded in these key flavor components through the harvest season, and between breeding selections and cultivars, confirmed the value of collecting these data in all future years. A Felix Instruments F-750 analyzer for non-destructive fruit quality testing, on loan to us through Agreement No. 58-8042-8-016, was successfully calibrated for strawberry brix. When calibration for strawberry pH is complete, the F-750 can be used to breed strawberries that retain desired brix and pH levels in refrigerated storage for eventual enjoyment by consumers. In support of Objective 2a, ARS scientists in Beltsville, Maryland, established observation plots of 46 repeat-fruiting strawberries selected from the breeding program in 2017 for comparison with 3 cultivars, all grown under low tunnels. A field of 5,160 seedlings was established, from which up to 75 additional breeding selections will be made. In support of Objective 2b, ARS scientists in Beltsville, Maryland, completed field testing of plastic types to cover low tunnels. Data will be analyzed to determine which plastic should be used in the breeding program to cover the low tunnels used to evaluate potential repeat-fruiting strawberry cultivars. In support of Objective 2c, ARS scientists in Beltsville, Maryland, have been unable to identify collaborators willing to address the problem of epistasis (the effect of one gene on another independent gene) in mapping inheritance to repeat fruiting. In support of Objective 3, ARS scientists in Beltsville, Maryland, have recorded the number of overgrown stems, known as stolons or runners, produced from each of 350 siblings of a strawberry population designed to study inheritance of this trait which is crucial to commercial nursery production of strawberry plants for sale to growers. DNA and RNA, extracted and pooled from non-runnering plants as well as from runnering siblings, have been submitted for sequencing to identify the genes responsible for the trait. In support of Objective 4, ARS scientists in Beltsville, Maryland, have acquired an APHIS permit to import from Mississippi the strawberry pathogen isolates that cause anthracnose crown rot. Convenient and secure testing facilities have been located. Seed from commercial cultivars known to be resistant or susceptible to anthracnose crown rot have been obtained from harvested fruits. Mutated seed of diploid strawberry have been accumulated. A testing schedule that does not interfere with the breeding program schedule has been developed.