2019 ASHS Annual Conference

Over the last 50 years, breeding has profoundly altered the productivity of garden strawberry (Fragaria × ananassa), greatly distancing modern long shelf-life mass-production cultivars from short shelf-life heirloom cultivars. One of the more profound changes over that period was the introduction of wild species alleles by Royce S. Bringhurst that eliminated photoperiod sensitivity, thereby creating so-called ‘day-neutral’ cultivars. The development and introduction of long-day flowering cultivars expanded the production window from a few months to year round in mild maritime California climates. Selection in parallel for mass-production traits has delivered day-neutral cultivars with high yields of large, well-formed, firm, visually appealing, extended shelf-life fruit that can withstand the rigors of harvest, handling, storage, and long-distance shipping. These breeding advances are anecdotally well known, however, genetic gains for yield and many other mass-production traits have not been well documented or carefully studied in strawberry. Here we describe the results of three years of field testing of day-neutral cultivars developed over the last three decades and show that genetic gains for yield have been dramatic in the University of California, Davis breeding program, with present-day cultivars yielding 50 to 150% more fruit per hectare than their predecessors. Cumulative marketable yields of three newly developed day-neutral cultivars (UC9, UC11, and UC12) ranged from 246,235 to 262,070 clamshells/ha compared to 203,101 to 210,277 clamshells/ha for check cultivars (Monterey and Cabrillo). The ranks of cultivars were highly consistent over years, locations, and production systems, with a broad-sense heritability of 0.70. UC9 and UC12 produced significantly fewer runners than check cultivars in coastal California production environments, a characteristic predicted to significantly decrease runner-trimming labor costs. UC12, the highest yielding cultivar, was found to be highly resistant to Fusarium and Verticillum wilt, the two most damaging soil-borne pathogens in organic and conventional production systems in California. The cultivars we tested maintained shelf-life for nearly 21 days (the maximum duration of our post-harvest testing). UC9, UC11, and UC12 have the potential to deliver exceptionally high yields of marketable fruit over the long harvest season in coastal California and comparable long-day production environments.