Strawberry plant named ‘UC Keystone’

Abstract

UC Keystone is a day-neutral flowering cultivar of a strawberry plant that produces exceptionally high yields of firm, long shelf-life fruit and is resistant to Fusarium wilt, Verticillium wilt, and Phytophthora crown rot.

Claims

1. A new and distinct cultivar of strawberry plant named UC Keystone, substantially as described and illustrated herein.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The colors in the photograph are depicted as nearly true as is reasonably possible to obtain in color reproductions of this type.

(2) FIG. 1 depicts fruit of UC Keystone.

(3) FIG. 2 shows 5-month old UC Keystone plants.

DETAILED DESCRIPTION

Botanical Description

(4) Botanical descriptors of UC Keystone are provided in Table 1. The descriptors were collected in the spring and summer of 2022 from plants grown in Santa Maria, California. Plants evaluated in the spring were 6 months old. Plants evaluated in the summer were 8 months old. Colors are designated with reference to The Royal Horticultural Society (R.H.S.) Colour Chart, Sixth Edition, 2015. The characteristics of UC Keystone may vary in detail, depending upon environmental factors and culture conditions.

(5) TABLE-US-00001 TABLE 1 .sup.aMean values were estimated from nine samples per trait. Range (Mean.sup.a) or Color (RHS Colour Category Trait Unit Designation) Foliar Plant height mm 300-360(328) Foliar Plant spread mm 520-620(566) Foliar Plant growth habit Semi-upright Foliar Position of the Above inflorescence in relation to foliage Foliar Mid-tier leaflet length mm 90-120(102) Foliar Mid-tier leaflet width mm 110-140(129) Foliar Petiole length mm 230-290(250) Foliar Stipule core color color code Moderate Yellow Green (146 C) Foliar Stipule margin color color code Moderate Yellow Green (146 A) Foliar Stolons/nursery count 10-12(11.0) mother plant Foliar Stolon color color code Brilliant Yellow Green (150 C) Foliar Leaf color, adaxial color code Moderate Olive Green (147 A) Foliar Leaf color, abaxial color code Moderate Yellow Green (147 B) Foliar Leaf, blistering Medium Foliar Leaf, glossiness Medium Foliar Leaf, shape of the Obtuse base of terminal leaflet Flower Petal, arrangement of Overlapping petals Flower Petal number count 5-6(5) Flower Petal length mm 10-15(12) Flower Petal width mm 10-15(12) Flower Calyx diameter mm 25-40(35) Flower Corolla diameter mm 19-27(21) Flower Calyx, size in relation Larger to corolla Flower Flower, Stamen Present Flower Sepal number count 10-15(11) Flower Calyx Color color code Moderate Olive Green (137 A) Flower Upper Petal Color color code White (NN155 D) Flower Lower Petal Color color code White (NN155 D) Flower Stamen number count 22-32(27) Fruit Achene Color color code Greenish Brilliant Fruit Position of achenes Yellow (4 A) Below Surface Fruit Fruit length mm 43-56(50) Fruit Fruit width mm 30-38(34) Fruit Shape Conical Fruit Size of hollow core mm 0-10(6) Fruit External Fruit color code Vivid Red (44 A) (exterior) color Fruit Fruit flesh color color code Vivid Reddish Orange (33 A) Fruit Fruit core color color code Moderate Reddish Orange (35 A&B) Fruit Fruit size g/fruit 22-30(26)

(6) The time of the beginning of flowering is late February, 4 months post-planting.

Fusarium Resistance

(7) Marker-assisted selection was employed to identify individuals predicted to be heterozygous or homozygous for the dominant (favorable) alleles for a Fusarium wilt resistance locus (FW1) and the PERPETUAL FLOWERING (PF) locus. The genotypes predicted by PF- and FW-linked SNPs for UC Keystone were PFpf and FW1fw1. The predicted genotypes were confirmed with a 50,000 Aximo SNP array (Hardigan et al, 2020).

(8) The dominant FW1 allele confers resistance to Fusarium wilt race 1, cause by Fusarium oxysporum f.sp. fragariae. Fusarium resistance was further tested by three years of replicated testing of bare-root plants artificially inoculated with AMP132, a race 1 isolate of the pathogen. The resistance of UC Keystone to Fusarium wilt was compared to that of UC Golden Gate, San Andreas (U.S. Plant Pat. No. 19,975), which is heterozygous FW1fw1 Fusarium wilt-resistant; and to susceptible (homozygous recessive (fw1fw1)) varieties Monterey, UCD Royal Royce, and UCD Valiant. UC Keystone, UC Golden Gate, and San Andreas were symptomless in these Fusarium wilt screening trials over three years (Table 2) with the mean disease scores in the highly resistant range and were not significantly different. The mean disease scores for Monterey, UCD Royal Royce, and UCD Valiant were significantly greater than for UC Keystone (ordinal scores increase as disease symptoms increase).

(9) UC Keystone resistance to Verticillium wilt and Phytophthora crown rot (PhCR) was also evaluated (see, also Table 3) in comparison to UC Golden Gate, Monterey, UCD Royal Royce, and UCD Valiant. UC Keystone and UC Golden Gate are moderately resistant to these diseases. Their resistance phenotypes are not significantly different from those of San Andreas and Monterey, and other commercially important cultivars.

(10) TABLE-US-00002 TABLE 2 Across-year estimated-marginal means (EMMs).sup.a for Fusarium wilt, Verticillium wilt, and Phytophthora crown rot (PhCR) resistance scores.sup.b for UC Keystone, UC Golden Gate, UCD Valiant, UCD Royal Royce, San Andreas, and Monterey observed in 2019-20, 2020-21, and 2021-22 disease resistance screening trials in Davis, CA. Test Cultivar Check Check Cultivar Cultivar Disease.sup.c EMM.sup.d EMM t.sup.e p-value.sup.f Fusarium Wilt UCD Valiant 1.25 2.88 ?3.86 0.0003 UCD Royal 2.98 ?4.12 0.0001 Royce San Andreas 1.15 0.19 0.85 Monterey 3.36 ?4.67 <0.0001 UC Golden Gate 1.17 0.19 0.85 Verticillium UCD Valiant 2.12 1.93 0.43 0.67 Wilt UCD Royal 2.31 ?0.44 0.66 Royce San Andreas 1.29 1.19 0.24 Monterey 2.36 ?0.46 0.64 UC Golden Gate 1.97 0.34 0.74 Phytophthora UCD Valiant 2.44 2.25 0.35 0.73 Crown Rot UCD Royal 2.33 0.21 0.84 Royce San Andreas 1.83 0.85 0.40 Monterey 3.07 ?0.92 0.36 UC Golden Gate 2.25 0.34 0.73 .sup.aEMMs were estimated from four replications/entry/year over three years (12 observations/entry), except for Fusarium, where additional screening in 2022 resulted in 24 observations/entry. .sup.bThe ordinal symptom rating scales were identical for each disease: 1 = highly resistant, 2 = moderately resistant, 3 = moderately susceptible, 4 = susceptible, and 5 = highly susceptible. .sup.cThe fungal pathogens causing these diseases are Fusarium oxysporum f. sp. fragariae (Fusarium wilt), Verticillium dahliae (Verticillium wilt), Phytophthora cactorum (Phytophthora crown rot). .sup.dThe test cultivars were UC Keystone (shown in the upper half of the table) and UC Golden Gate (shown in the lower half of the table). .sup.et-statistics for linear contrasts (EMM.sub.1-EMM.sub.2) between the EMMs for UC Keystone or UC Golden Gate and check cultivars. .sup.fThe probability of a greater t-statistic by chance for tests of the null hypothesis of no difference between EMMs (H.sub.0: EMM.sub.1 = EMM.sub.2).

Photoperiod Insensitive Phenotype

(11) The dominant PF allele is necessary for photoperiod insensitive flower in cultivated strawberry. The predicted photoperiod insensitive phenotype of UC Keystone was confirmed through three years of on-farm testing in Sana Maria, California and Prunedale, California. UC Keystone consistently flowered and fruited throughout the commercial day-neutral growing seasons in Nipomo (35.0N) and Prunedale (36.8N) where daylengths ranged from 9.8 to 14.7 hours.

Field Evaluations

(12) Three seasons of advanced testing of selected day-neutral hybrids originating from the 2017-18 breeding cycle, starting with ninety-four in 2018-19 and finishing with six in 2021-22, one of which was UC Keystone, were completed. Comparison cultivars were UC Golden Gate, Monterey, UCD Royal Royce, and UCD Valiant.

(13) Clones (asexually propagated bare-root plants) for the first year of testing (Phase I in 2018-19) were produced in Winters, California. Clones for subsequent years of testing (Phase II in 2019-20 and 2020-21 and Phase III in 2021-22 and 2022-23) were produced in commercial high-elevation nurseries (Dorris, California) using standard production and propagation practices and post-harvest chilling treatments optimized for the day-neutral market segment. Clones were harvested in late October, trimmed, and directly planted in late October and early November of each year.

(14) For on-farm yield trials, plants were grown in two 10-plant plots in Phase I and two 20-plant plots in Phase II yield trials, and two 500- or 1,000-plant strips in Phase III yield trials. The plots were arranged in randomized complete blocks experiment designs in commercial production fields. These experiments were grown using the management practices, bed configurations, plastic mulches, planting densities, planting dates, irrigation, fertilization, and pesticide application decisions and schedules, and harvest schedules of our cooperators.

(15) Marketable fruit yield, count, and size were recorded at each harvest. Collection and analysis of 18,526 observations were employed for these traits to support statistical analyses.

Fruit Quality

(16) Fruit from early and peak season harvests from every trial were performed to phenotype hybrids for firmness, total soluble solids (TSS=Brix), and titratable acidity (TA). The peak and late season fruit from four environments were stored at 4? C. and screened for post-harvest perishability over 14 days. These samples were phenotyped for weight, TSS, TA, firmness, gloss, and leakage at 0, 7, and 14 days post-harvest (DPH). Over three growing seasons, 2,273 phenotypic observations were collected for fruit quality traits at harvest to support statistical analyses and selection decisions.

(17) Plants were assessed for flavor and aroma through informal hedonic testing in the field and laboratory by various individuals. Although specific volatile organic compounds (VOCs) known to affect aroma were not selected for, selection pressure for enhanced flavor and aroma was applied and VOC profiles were analyzed for 152 cultivars and other hybrids over two years of on-farm testing. UC Keystone was among the hybrids phenotyped for VOC. These data were used to assess the effect of subjective olfactory and gustatory assessments on aroma profile changes. VOC analyses were performed using solid phase microextraction (SPME) gas chromatography-mass spectroscopy of fruit samples collected from early and peak season harvests over two years from on-farm yield trials in Santa Maria and Prunedale, California. Although at least 360 VOCs have been identified in developing strawberry receptacles, aroma and flavor are dominated by fewer than 10. Data for approximately 52 VOCs affecting aroma (58,488 phenotypic observations) were collected and analyzed to support statistical analyses. Data for three VOCs (?-decalactone, mesifurane, and linalool) that are predicted to contribute towards the improved flavor of UC Keystone and UC Golden Gate are provided.

(18) The fruit quality of UC Keystone equal or exceeds the fruit quality and shelf life standards of long shelf life (LSL) cultivars designed for prolonged cold storage and long-distance shipping. Table 3 provides a comparison of the cumulative marketable fruit yields and other fruit traits.

(19) TABLE-US-00003 TABLE 3 Across-environment estimated marginal means (EMMs) for cumulative marketable fruit yield and other fruit traits for UC Keystone and comparison cultivars grown on commercial farms in Nipoomo and Prunedale, CA over three growing seasons (2019-20 to 2021-22).sup.a. UC Comparison Comparison Keystone Cultivar Trait.sup.a Cultivar EMM EMM t.sup.b p-value.sup.c Yield Monterey 103,710 88,323 1.42 0.16 (lb/acre) UCD Valiant 91,783 1.10 0.28 UCD Royal 89,044 1.35 0.18 Royce UC Golden 95,730 0.73 0.47 Gate Size Monterey 28.0 29.7 ?3.23 0.001 (g/fruit) UCD Valiant 33.0 ?8.91 <0.0001 UCD Royal 28.8 ?1.39 0.16 Royce UC Golden 28.7 ?1.20 0.23 Gate Firmness Monterey 260.6 239.1 1.96 0.05 (g-force) UCD Valiant 297.1 ?2.93 0.005 UCD Royal 349.9 ?7.18 <0.0001 Royce UC Golden 303.7 ?3.25 0.002 Gate TSS (%) Monterey 8.29 8.89 ?4.19 0.0001 UCD Valiant 7.37 5.78 <0.0001 UCD Royal 7.57 4.55 <0.0001 Royce UC Golden 7.84 2.59 0.01 Gate TA (%) Monterey 0.77 0.76 ?0.39 0.70 UCD Valiant 0.82 ?2.97 0.005 UCD Royal 0.82 ?2.87 0.006 Royce UC Golden 0.85 4.21 0.0001 Gate TSS/TA Monterey 11.01 10.44 ?2.69 0.01 UCD Valiant 9.20 6.35 <0.0001 UCD Royal 9.55 5.12 <0.0001 Royce UC Golden 9.45 5.19 <0.0001 Gate .sup.aCumulative marketable fruit yields were estimated from fruit harvested on commercial schedules (once or twice weekly) over the entire day-neutral growing season on each farm. Fruit firmness, total soluble solids (TSS), and titratable acidity (TA) were measured from multiple fruit/replication sampled from two harvests/trial. EMMs and test statistics were estimated from the phenotypes of fruit harvested from two 24-plant plots/entry/environment. .sup.bt-statistics for linear contrasts (EMM.sub.1-EMM.sub.2) between UC Keystone and check cultivar EMMs. .sup.cThe probability of a greater t-statistic by chance for tests of the null hypothesis of no difference between EMMs (H.sub.0: EMM.sub.1 = EMM.sub.2).

(20) UC Keystone produced large fruit (28.0 to 28.7 g/fruit) in the on-farm trials (Table 3). Their fruit weights were in the normal range for mass-produced day-neutral cultivars in California and above the market critical threshold needed for cost-effective hand harvest (labor costs increase as fruit size decreases).

(21) UC Golden Gate fruit were significantly firmer (303.7 g-force) than UC Keystone (260.6 g-force; p=0.0002) and Monterey (239.1 g-force; p<0.0001). The firmness of these cultivars exceeded the threshold (>230 g-force) necessary for minimizing harvest and post-harvest losses and delivering a high quality product to markets over long distances.

(22) The sweetness and sourness profiles of UC Keystone and UC Golden Gate are slightly different. Total soluble solids (TSS) were slightly greater for UC Keystone (8.33) than UC Golden Gate (7.85; p=0.008), whereas titratable acidity (TA) was greater for UC Golden Gate (0.83) than UC Keystone (0.74; p=0.0003). The TSS/TA ratio (a measure of perceived sweetness) was significantly greater for UC Keystone (11.66) than UC Golden Gate (9.86; p=0.0001) and non-significantly greater than Monterey (10.44; p=0.01), whereas the TSS/TA ratio for UC Golden Gate was significantly lower than Monterey (p<0.0001). Hence, the sweetness and perceived sweetness ratings for UC Keystone and Monterey were virtually identical and greater than that of UC Golden Gate.

(23) UC Keystone and UC Golden Gate were identified to have improved aroma from subjective olfactory and gustatory assessments of fruit. Solid phase microextraction (SPME) GC-MS analyses of volatile organic compounds (Table 4) suggested that part of the improved flavor of UC Keystone and UC Golden Gate can be attributed to an increase in ?-decalactone (5-hexyloxolan-2-one), the most abundant lactone found in strawberry. This VOC, which imparts an intense-peach flavor, is abundant in Albion (U.S. Plant Pat. No. 16,228) and absent in Monterey.

(24) TABLE-US-00004 TABLE 4 Across-year estimated-marginal means (EMMs).sup.a for ?-decalactone, mesifurane, and linalool concentrations.sup.a in ripe fruit of UC Keystone, UC Golden Gate, and comparison cultivars harvested in 2020-21 and 2021-22 from on-farm yield trials in Nipomo, CA. ?-decalactone mesifurane linalool Cultivar EMM EMM EMM Monterey 0 1,025,275 58,682 UCD Royal Royce 7,253 247,148 0 UCD Valiant 14,406 213,015 1,374 UC Keystone 34,740 156,584 20,783 UC Golden Gate 7,273 241,300 6,265 Albion 132,592 991,288 17,942 LSD.sup.b 109,763 146,678 26,860 .sup.aEMMs were estimated from fruit sampled from two 20- or 40-plant plots/entry/year. The relative concentrations of volatile organic compounds (ng/g dry weight) were estimated from the raw solid phase microextraction (SPME) GC-MS data (peak area in counts) and normalized samples. .sup.bLeast significant differences are shown for a false-positive probability of p = 0.05.

(25) UC Keystone and UC Golden Gate meet or exceed the shelf life requirements for mass-produced cultivars developed for cold storage and long distance shipping in California. Minimal declines were observed in the deterioration of fruit firmness and other fruit quality traits over 14 days of post-harvest cold storage using fruit sampled from peak and late season harvests No statistically significant differences for fruit weight, TSS, TA, or leakage between UC Keystone and UC Golden Gate and comparison cultivars were observed.

Fruit Production CharacteristicsField Trials

(26) The number of harvests ranged from 40 to 61 in each trial to assess UC Keystone fruit production in comparison to that of UC Golden Gate Monterey, UCD Royal Royce, and UCD Valiant. Marketable fruit yield, count, and size were recorded at each harvest. Collection and analysis of 18,526 observations was performed for these traits to support statistical analyses.

(27) Statistics are shown for linear contrasts between the estimated marginal means (EMMs) for UC Keystone, UC Golden Gate , and comparison cultivars across environment (2 locations 3 years) and for individual environments to highlight variation in planting dates, the number of harvests, harvest ranges, and production practices (Table 5). EMMs were estimated from two 20-plant plots (replications)/entry/environment in 2020 and 2021 and two 540-plant plots in 2022.

(28) TABLE-US-00005 UC Compare Keystone Cultivar Comparison EMM EMM Location Season Cultivar (lb/a) (lb/a) Nipomo 2019-20 Monterey 88,028 64,797 UC Royal Royce 79,625 UC Valiant 90,853 UC Golden Gate 82,971 Prunedale 2019-20 Monterey 103,149 73,300 UC Royal Royce 101,146 UC Valiant 81,841 UC Golden Gate 103,065 Nipomo 2020-21 Monterey 99,214 70,682 UC Royal Royce 93,142 UC Valiant 107,279 UC Golden Gate 99,935 Prunedale 2020-21 Monterey 115,908 97,546 UC Royal Royce 128,842 UC Valiant 119,684 UC Golden Gate 123,669 Nipomo 2021-22 Monterey 56,691 69,976 UC Royal Royce 39,241 UC Valiant 57,602 UC Golden Gate 59,740 Prunedale 2021-22 Monterey 158,914 152,127 UC Royal Royce 92,924 UC Valiant 93,437 UC Golden Gate 104,999 Yield Change Location (%).sup.b t.sup.c p-value.sup.d Nipomo 35.9 3.70 0.004 10.6 1.03 0.33 ?3.1 ?0.45 0.66 6.1 0.84 0.42 Prunedale 40.7 5.56 0.0002 2.0 0.37 0.72 26.0 3.97 0.002 0.1 0.02 0.99 Nipomo 40.4 3.16 0.01 6.5 0.67 0.52 ?7.5 ?0.89 0.39 ?0.7 ?0.08 0.94 Prunedale 18.8 2.92 0.01 ?10.0 ?2.05 0.06 ?3.2 ?0.60 0.56 ?6.3 ?1.23 0.24 Nipomo ?19.0 ?5.17 <0.0001 44.5 5.54 <0.0001 ?1.6 ?0.29 0.78 ?5.1 ?0.97 0.34 Prunedale 4.5 1.25 0.23 71.0 9.89 <0.0001 9.8 70.1 <0.0001 51.3 8.08 <0.0001 .sup.aLinear contrasts between estimated marginal means (EMMs) for UC Keystone and comparison cultivars were estimated for each environment. EMMs were estimated from two 20-or 40-plant plots/entry within each environment. Cumulative marketable fruit yields were estimated from fruit harvested on commercial schedules (once or twice weekly) over the entire day-neutral growing season on each farm. .sup.bThe yield change percentage was estimated by (EMM.sub.1 ? EMM.sub.2)/EMM.sub.2 ? 100. .sup.ct-statistics for linear contrasts (EMM.sub.1 ? EMM.sub.2) between the EMMs for UC Keystone and comparison cultivars. .sup.dThe probability of a greater t-statistic by chance for tests of the null hypothesis of no difference between EMMs (H.sub.0: EMM.sub.1 = EMM.sub.2).

(29) UC Keystone and UC Golden Gate were the highest yielding cultivars in these trials. When averaged across environments, however, the yields of UC Keystone, UC Golden Gate, and the three comparison cultivars were not statistically different. Thus, UC Keystone has yields at least equal to the Fusarium wilt-susceptible comparison cultivars.

(30) The cumulative marketable fruit yields of UC Keystone were 6,787 to 29,849 lb/a greater than Monterey in five environments and 13,285 lb/a lb/a less than Monterey in one environment (Nipomo 2021-22) (Table 5).

(31) The cumulative marketable yield plots for each environment highlight the differences among cultivars and growing seasons. The yields of Monterey were below and separated from UC Keystone, UC Golden Gate, and the other comparison cultivars in the first two growing seasons. Yields dropped in the last growing season (2021-22) in Nipomo especially compared to previous years, with less separation among cultivars.

(32) The cumulative marketable fruit yields of UC Keystone and UC Golden Gate were not significantly different in five of six test environments or across environments (Tables 3 and 5). The yield of UC Keystone was significantly greater than UC Golden Gate in one environment (Prunedale 2021-2022). The reasons for yield decreases for UC Golden Gate, UCD Royal Royce, and UCD Valiant in the 2021-22 Prunedale trial were not clear. The affected plants ultimately recovered, however, and produced an abundance of fruit later in the season.

(33) UC Keystone is thus a highly productive Fusarium wilt resistant cultivar for the day-neutral segment that meets or exceeds the shelf life, flavor, and fruit quality characteristics of Monterey.