HORTSCIENCE 52(11):1496–1500. 2017. doi: 10.21273/HORTSCI12025-17 of PF releases from the University of Cal- ifornia strawberry breeding program. The genetics behind PF are of consider- Perpetual Flowering in Strawberry able economic interest to growers, the food industry, and global consumers, who, with Species increased global production, can now enjoy strawberries every day of the year. Studies Weijian Cai have identified genes or loci underlying the Institute of Pomology, Jiangsu Academy of Agricultural Sciences/Jiangsu control of flowering habit in the diploid Key Laboratory for Horticultural Crop Genetic Improvement, 50 Zhongling alpine and in the common garden strawberry Street, Nanjing, Jiangsu 210014, China (Gaston et al., 2013; Iwata et al., 2012; Koskela et al., 2012; Perrotte et al., 2016a, Jason D. Zurn, Nahla V. Bassil, and Kim E. Hummer1 2016b; Salinas et al., 2017). In the alpine USDA National Clonal Germplasm Repository, 33447 Peoria Road, strawberry, flowering habit is governed by Corvallis, OR 97333 the floral repressor FvTFL1 located on chro- mosome 6 (Iwata et al., 2012; Koskela et al., Additional index words. Fragaria 3ananassa, day-neutral, remontant, repeat blooming, 2012). FvTFL1 suppresses the flowering in- germplasm, genetic resources ducing gene, Flowering Locus T, FvFT1, which is also located on chromosome 6 Abstract. The genetic control of flowering habit in many species of Fragaria has not been (Iwata et al., 2012; Koskela et al., 2012). A well studied. Identification of flowering traits and patterns for these taxa could be used in 2 bp deletion in FvTLF1 prevents it from the quest for perpetual flowering (PF) genes and for the octoploids, broaden the genepool suppressing FvFT1, resulting in PF (Iwata of available PF parents for breeding programs. As such, clones from the Fragaria et al., 2012; Koskela et al., 2012). In the germplasm collection housed at the USDA-ARS National Clonal Germplasm Repository common garden strawberry, PF can be in- in Corvallis, OR, were evaluated to describe flowering habits in various taxa and identify duced by silencing FaTFL1,anFvTFL1 PF clones. Flower presence was recorded monthly for 962 clones of 36 taxa from the first homolog; however, FaTLF1 is not responsi- of May through October in 2015 and 2016 to determine flowering habit and pairwise ble for the PF phenotype conferred by the comparisons between taxa were examined using Pearson’s Chi-squared test. Taxa with Wasatch source (Nakano et al., 2015; Per- the largest percent of PF accessions were F. vesca subsp. vesca f. semperflorens, F. vesca rotte et al., 2016a). The Wasatch source of PF subsp. vesca f. alba, F. vesca subsp. americana, and F. virginiana subsp. glauca. These is conferred by the FaPFRU locus on chro- taxa had similar flowering habits to each other but were significantly different (a =0.05) mosome 4B (Gaston et al., 2013; Perrotte from most other taxa in which the seasonal flowering (SF) trait was predominant. Fifteen et al., 2016a). While the gene controlling PF clones that demonstrated the PF phenotype in both 2015 and 2016 were identified. is not known, a homolog of FvFT2 was Differing genetic controls have been observed for flowering habit in F. 3ananassa and F. proposed as the most likely candidate (Gaston vesca. Additional studies are needed to determine genetic control of flowering in other et al., 2013; Perrotte et al., 2016a). Interest- Fragaria taxa. ingly, FaPFRU inversely controls both flow- ering and runnering (Gaston et al., 2013; Perrotte et al., 2016a). The dominant allele The cultivated octoploid garden straw- ing,’’ and ‘‘long day plants’’ have all been of FaPFRU induces more inflorescences than · berries, Fragaria ananassa, are classified used to describe plants which flower multiple stolons, and in homozygous recessive plants, based on their flowering habit into those that times and produce multiple crops over the more stolons than inflorescences are pro- flower and fruit mostly once in the Spring and course of the summer. We chose the terms duced given the study conditions (Gaston those that continue to flower and fruit as long ‘‘seasonal flowering’’ (SF) and ‘‘perpetual et al., 2013). Despite the body of work that ° as temperatures are moderate (below 30/26 C flowering’’ (PF) to describe flowering habit has been done in F. vesca and the Wasatch day/night) (Darrow, 1966; Hancock, 1999). in this study (Gaston et al., 2013). source of PF in F. ·ananassa, very little is Multiple terms have been used interchange- During most of the 1900s, the cultivars known about the genetics underlying flower- ably to describe strawberry flowering habit. produced were SF, blooming in the spring ing habit in other F. ·ananassa PF sources or ‘‘Short day,’’ ‘‘once flowering,’’ ‘‘seasonal and producing one fruit crop per summer. PF Fragaria taxa. flowering,’’ ‘‘single cropping plants,’’ or forms of the diploid alpine strawberry, F. Seasonal cues, such as temperature, light ‘‘June-bearing’’ has been used to describe vesca subsp. vesca f. semperflorens, were conditions, and daylength, can have large plants which bloom in the spring and produce one common in Europe when Linnaeus named effects on the occurrence of PF (Andres and fruit crop per summer. The terms ‘‘everbearing,’’ the genus (Duchesne, 1766). F. ·ananassa Coupland, 2012; Salinas et al., 2017). Under ‘‘remontant,’’ ‘‘day-neutral,’’ ‘‘perpetual flower- with the PF trait were recorded since the mid different temperature conditions, the flower- 1860s. ‘Gloede’s seedling’ was the first widely ing habit of strawberries has been observed to known PF garden strawberry (Richardson, be under either qualitative or quantitative 1914). Others, such as ‘Laxton’s Perpetual’, genetic control (Sønsteby and Heide, 2007). Received for publication 13 Apr. 2017. Accepted ‘Mastadon’, and ‘Rockhill’, were early pa- Moreover, under long-day conditions (>14 h for publication 29 June 2017. rental types for this trait (Clark, 1937; Weijian Cai was supported through a fellowship daylight), SF individuals behave as PF plants from the Jiangsu Academy of Agricultural Sciences, Powers, 1954; Richardson, 1914). These at low temperatures (Darrow, 1936; Darrow Nanjing, China, and National Crop Germplasm cultivars that extended the fruit production and Waldo, 1934). The PF trait can also occur Resources Preservation of China #2016NWB007. season and increased productivity were where latent buds develop through the re- We appreciate the support of ARS CRIS # termed ‘‘everbearing.’’ The discovery by moval of inflorescences during the growing 2027-21000-044-00D for funding the maintenance Bringhurst in 1955, of what became known season (Sugiyama et al., 2004). and evaluation of Fragaria genetic resources. We as the ‘‘day-neutral’’ F. virginiana subsp. Within the genus Fragaria, 22 species, also appreciate the technical assistance of Jim glauca clone from the Wasatch Mountains multiple species hybrids, and numerous sub- Oliphant, Nguyen Van Kien, Tran Thi Thu Hoai, in Utah, was a pivotal event causing changes species have been globally described (Liston and Debra Hawkes for assistance in flower removal in strawberry production practices in Cali- for this study. We greatly appreciate the com- et al., 2014). Identification of flowering traits ments from reviewers who improved the article fornia and the world (Bringhurst et al., 1989, for individuals of these taxa could broaden presentation. 1990; Faedi et al., 2002; Salinas et al., 2017; the genepool of available PF parents for 1Corresponding author. E-mail: Kim.Hummer@ Simpson, 1993; Zurawicz and Masny, 2002). breeding programs. A recent study examined ars.usda.gov. This clone was the key in producing a family recurrent bloom of American octoploid 1496 HORTSCIENCE VOL. 52(11) NOVEMBER 2017 strawberry species (Hummer et al., 2016). berries were growing was unavailable for sentatives (10 taxa; Table 1). For the 28 taxa The present study is an expansion of that this study. Temperatures from the local with greater than four individuals, two-by- work. The objectives of this project were to Corvallis, OR, airport for 2015 and 2016 two contingency tables were created to con- screen diverse strawberry genetic resources were used to estimate regional cumulative duct comparisons of the flowering data where for flowering phenotype and to identify growing degree days and mean daily temper- the two categories were ‘‘species’’ and particular PF clones. Innovative breeders atures (Fig. 1, NOAA, 2017). Growing De- ‘‘flowering habit,’’ either PF or SF. Pearson’s are using secondary and tertiary gene pools gree Day units were computed as the difference Chi-squared test with the ‘N-1’ correction in their crosses as well as introgressing traits between the daily average temperature and the (Campbell, 2007) was used to determine if from new wild collections within the primary base temperature (Daily Ave. Temp. – Base the flowering habits of species differed. The gene pool to seek improvements and berries Temp.). One unit is accumulated for each Benjamini–Hochberg method was used to with novel traits (Hancock et al., 2010). This degree Fahrenheit when the average tempera- control for experiment-wide false discovery study could expand taxa or particular in- ture is above the base temperature. Negative rate during pairwise comparisons (Benjamini dividuals for consideration as parents where numbers were discarded. This was done for and Hochberg, 1995). Calculations were PF is desirable. each day of the months from January through performed in R version 3.2.5 (R Core Team, June and summed for each year. 2016) using a custom R script (Supplemental Materials and Methods Phenotyping. Flower presence was recorded file 1). in 2015 and 2016, on the first day of the month Germplasm. For this phenotyping study, from May through October. Inflorescences Results 962 clones from 38 strawberry taxa and and complete trusses were removed after hybrids were observed at the USDA-ARS scoring. Plants flowering only before Au- Many of the taxa had individuals that National Clonal Germplasm Repository gust first were considered SF, and those were PF; however, flowering habit for the (NCGR) in Corvallis, OR (Table 1).