Short-day Strawberry Research Articles

Impact of Pre-Plant Fertilizer Rates in Combination with Polysulphate® on Soil Nitrogen Distribution and Yield of Short-Day Strawberries (Fragaria × ananassa cv. Camarosa)

Strawberries are by far the most produced soft fruit (blueberries, raspberries, blackberries, and strawberries) worldwide, with China and the US being the two countries with the most production. In the US, strawberries reached a farm gate value of more than USD 3 billion in 2023 and are predominantly grown in the open field on an annual cycle in hilled-up soil beds using plastic mulch (plasticulture). This process relies on adequate pre-plant fertilizer application for plant establishment and fruit development. In North Carolina (US), it is current practice to apply pre-plant fertilizer containing 67 nitrogen (N) kg/ha; however, with increasing fertilizer costs and environmental concerns, questions remain as to whether or not pre-plant full-spectrum fertilizer rates can be reduced and substituted with organic low-N fertilizer sources, such as Polysulphate, without impacting yield or fruit quality. For this reason, field trials were established to evaluate the impact of pre-plant fertilizer rates on strawberry production (‘Camarosa’). Trials were conducted in the 2019–2020 and 2020–2021 seasons at two locations in North Carolina. The following N-rate pre-plant fertilizer treatments were applied: 80.1, 67.3, 54.1, 41.1, 33.6, 28.0, and 0 kg/ha. NO3 and NH4 content were frequently assessed in each replicate in the raised bed profile between planting and spring fertilizer application. Marketable and total strawberry yields were assessed over 6 weeks in the spring of 2020 and 2021. Our trial results showed that, especially in sandy soil, N rapidly declined under plastic within the first 8 weeks after pre-plant fertilizer application. However, no impact between pre-plant fertilizer rates and plant yield was observed. Treatments that contained Polysulphate and lower amounts of full-spectrum fertilizer showed significantly lower N concentrations in the soil while maintaining similar yields and fruit quality compared to grower-standard pre-plant fertilizer treatments. In summary, our results show that it is possible to reduce N content in pre-plant fertilizer by up to 50% compared to current recommendations without causing yield loss in short-day strawberry cultivars.

Growth and Yield of Strawberry Cultivars under Low Nitrogen Supply in Italy

Nitrogen plays a vital role in plants’ biochemical and physiological functions, and it contributes significantly to increasing plant yield and fruit quality. Plants that efficiently absorb and utilize nitrogen enhance the efficiency of fertilizers, reducing their input costs and preventing ecosystem damage. Thus, an adequate nitrogen supply can significantly improve plant growth, fruit quality, and nutritional value. This research focused on evaluating the plant vegetative and productive performance and fruit quality of three short-day strawberry genotypes (“Cristina”, “Romina”, and “Sibilla”) that were fertilized with different amounts of nitrogen, in a crop that was protected under a plastic tunnel. The trial was conducted during two cultivation cycles. The nitrogen rates were 113, 90, and 68 kg/ha for the first year, and 118, 97, and 76 kg/ha for the second. Reduced nitrogen inputs did not significantly affect plant height, indicating that decreased nutritional intake does not harm plant development. The fruit sugar content value remained stable across all nitrogen supplies, as did the fruit titratable acidity. The cultivars maintained a medium fruit firmness at a 60% nitrogen supply, and the Chroma index was not affected. This study found that reducing nitrogen inputs did not have a significant negative impact on the three tested cultivars, making them suitable for cultivation with reduced nitrogen inputs to reduce the environmental impact and save growers’ inputs.

Influence of doses of nitrogen fertilizers and plant growth regulators on generative and vegetative productivity of strawberry (<i>Fragaria×ananassa</i> Duch.) in a repository

The modern system of nursery management of strawberry should be aimed at the use of adaptive cultivars and clones, allowing to obtain high yields of high-quality products. Optimization of mineral nutrition of plants, the use of plant growth regulators are necessary for the modern management of plant repositories, including strawberry. The study of ways to increase the yield of planting material of strawberry due to the simultaneous inhibition of the formation of peduncles is an urgent task in uterine plantings of the highest quality categories. The purpose of the research: to study the effectiveness of ways to reduce the components of generative productivity and increase the yield of planting material of strawberry garden varieties of short daylight hours and neutral daylight hours. In a field agrochemical experiment with plant growth regulators and doses of nitrogen fertilizer in the Stupinsky district of the Moscow region, on sod-podzolic soils, strawberry cv. Lubava, Tsaritsa, Nashe Podmoscov’e, Polka were studied. Doses of nitrogen fertilizer: N = 80 kg/ha and 120 kg/ha. Plant growth regulators: chlormequat chloride and gibberellic acid (GC3). As a result of the first year of research, it was found that the use of plant growth regulators and an increased dose of nitrogen in the strawberry cultivar of neutral day (Lyubava) contributed to a decrease in generative productivity, but also caused a decrease in the number of outlets. In shortday strawberry plants, a cultivar-specific reaction to fertilizer doses and plant growth regulators was observed, as a result of which it was revealed that the nitrogen dose N 80 kg /ha contributes to an increase in the generative productivity of plants cv. Nashe Podmoskov’e to a greater extent than cv. Polka and cv.Tsaritsa.

Selection of Short-Day Strawberry Genotypes through Multivariate Analysis.

Strawberries are produced in tropical regions using imported cultivars adapted to temperate and subtropical climates. These cultivars, under tropical conditions, produce below their genetic potential. Through multivariate analyses, the objective was to evaluate and select short-day strawberry genotypes based on intraspecific crosses, product characteristics, and fruit quality. The genotypes were obtained from the cross between 'Camino Real' (female parent) and the first-generation genotypes RVCA16, RVCS44, RVFS06, RVFS07, and RVDA11 (male parent), obtained in previous selections. The experimental design consisted of augmented blocks with standard controls, consisting of first-generation genotypes and commercial cultivars. The fruits were harvested and evaluated for productivity and post-harvest characteristics: total fruit mass (MTF), total number of fruits (TFN), average fruit mass (AFM), commercial fruit mass (CFM), fruit commercial number (CFN), average commercial mass of fruits (ACFM), total soluble solids (TSS), firmness (F), brightness (L), hue angle (°Hue), and chroma (C). The selection index of Mulamba and Mock (1978) was used with an intensity of 3% to obtain superior genotypes and submitted to multivariate analysis for comparative purposes. Of the 1500 genotypes evaluated, it was possible to select 44 genotypes with characteristics superior to the 13 controls. The RVDA11CR59 genotype showed better values for the attributes of interest, but the RVCS44CR population, from the cross between 'Camino Real' × RVCS44 ('Camarosa' × 'Sweet Charlie'), obtained the highest number (16) of individuals among those selected. Significant traits had high heritability but were not necessarily reflected in high selection gain. Coefficients of genetic variation were high, indicating sufficient genetic variability to select genotypes for these traits. When multivariate analyses were used, it was possible to group the selected genotypes into the same cluster according to the similarity and balance in the responses to the evaluated variables, demonstrating that these analyses help other parameters choose superior genotypes. The multivariate analysis allowed the selection of more balanced genotypes for production and post-harvest traits for tropical climates.

Breeding Short-Day Strawberry Genotypes for Cultivation in Tropical and Subtropical Regions

The main strawberry cultivars grown in tropical regions originated from breeding programs developed in temperate countries, which limit the expression of their maximum productive potential when grown in warm climates. Additionally, strawberry cultivation in these regions depends almost entirely on imported strawberry young plants, increasing production costs. Obtaining adapted cultivars with a lower requirement for the accumulation of chilling hours is the main objective of breeding programs in the southern hemisphere. Thus, the objective of this study was to evaluate short-day strawberry genotypes, pre-selected based on yield and fruit quality components through multivariate analysis, for cultivation in tropical conditions. Two experiments were performed. In the first one, 36 pre-selected genotypes and their parents were assessed based on productive traits (total fruit mass, commercial fruit mass, and mean mass of commercial fruits), soluble solids content, and fruit firmness. For selection, multivariate analysis was applied using the genotype (ideotype) selection index and principal component analysis. In the second experiment, the fruit of the best-ranked genotypes, the parents, and the Camarosa and Dover cultivars were assessed for soluble solids (SS), titratable acidity (TA), SS/TA ratio, ascorbic acid, phenolic compounds, and total anthocyanins. To identify the most promising genotypes, the data were analyzed using principal component analysis. The RVFS06CR-105, RVDA11CR-61, RVDA11CR-125, and RVCS44CR-130 were the most promising genotypes for cultivation in tropical conditions, based on yield and fruit quality components. The means found for these genotypes were higher than the commercial cultivars Dover, Camino Real, and Camarosa. The use of multivariate analysis was efficient in selecting the genotypes, with repeatability of information between the methods guaranteeing consistency in the information. The selected genotypes had higher yields than those used as the control, which is a promising result considering the independence in relation to genetic material, mainly in the expansion of the cultivation area in the tropical regions of the southern hemisphere. In addition, these genotypes are being evaluated in different tropical climate regions with the aim of validating them for submission to the registration and release process for farmers. Additionally, they are being used as a source of genes for crossings and new selections.

Effect of Low Temperature on Photosynthetic Physiological Activity of Different Photoperiod Types of Strawberry Seedlings and Stress Diagnosis

During the early growth stage of plants, low temperatures can alter cell permeability, reduce photosynthetic capacity, and have adverse effects on crop growth, development, and yield. Different strawberry cultivars have varying cold tolerance. In this study, we investigated the changes in cell permeability and photosynthetic activity of short-day and long-day types of strawberry cultivars under varying degrees of low-temperature stress, and evaluated the extent of cellular damage using photosynthetic and chlorophyll fluorescence parameters. The experiment utilized short-day strawberry cultivars ‘Toyonoka’ and ‘Red Face’, and long-day strawberry cultivars ‘Selva’ and ‘Sweet Charlie’ seedlings. Low-temperature treatments were set at −20, −15, −10, −5, 0, 5, and 10 °C for 12 h. The research demonstrated that short-day strawberries had greater tolerance to low temperatures, and all four strawberry cultivars began to experience low-temperature stress when the temperature was below 5 °C. A temperature range of 0 to −10 °C played a crucial role in causing severe cold damage to the strawberries. The low-temperature stress levels were constructed based on electrolyte leakage, with photosynthetic physiological characteristics serving as references. The study proves that the photosynthetic and chlorophyll fluorescence parameters can serve as effective probes for diagnosing low-temperature stress in strawberry seedlings, and their combination provides higher accuracy in identifying stress levels than any single type of parameter.

‘Cordial’ Strawberry

Cordial, a late-season, short-day strawberry (Fragaria ×ananassa Duch. ex Rozier), follows Keepsake as the second cultivar resulting from a U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) effort at Beltsville, MD, to develop strawberries with increased shelf life (Lewers et al., 2019). ‘Cordial’ and ‘Keepsake’ strawberries had similarly low proportions of fruit rot and degradation in 2 weeks of refrigerated storage compared with other cultivars and breeding selections. ‘Cordial’ has consistently provided very high yields and very low rot with no fumigation or fungicides in an annual plasticulture system at Beltsville, MD. ‘Cordial’ strawberries are

First Report of Sclerotinia Fruit and Crown Rot Caused by Sclerotinia sclerotiorum on Short-Day Strawberry in Maryland.

With over 1,000 producers in the Mid-Atlantic region, short-day strawberry (Fragaria x Ananassa Duch.) represents an economically important industry. In spring of 2016, a white rot was observed on strawberry stem, crown, and fruit tissue at two Maryland farms. Light to dark brown necrotic lesions, white mycelium and medium to large black sclerotia were present on petioles and fruit (Fig. 1). These symptoms were most consistent with Sclerotinia fruit rot and crown rot caused by Sclerotinia sclerotiorum (Lib.) de Bary (Maas 1998), not previously described in the region (Farr and Rossman 2019). Lesion margins were excised, surface disinfested (70% EtOH for 30 s and 0.1% NaClO for 1 min) and placed onto potato dextrose agar (PDA) amended with 0.03% tetracycline. Single hyphal tip cultures were obtained which formed fluffy white to tan mycelium, no asexual conidia, and numerous pigmented sclerotia resembling S. sclerotiorum (Bolton 2006). DNA was extracted from five isolates and the internal transcribed spacer (ITS) region was amplified by PCR using primers ITS1/ITS4; all five ITS sequences (533 bp) had 99-100% similarity with S. sclerotiorum (GQ375746) in Genbank. Sequences of SL1380 and SL1382 were submitted to NCBI under the accession numbers MK429976 and MK429977, respectively. These two isolates were evaluated for abilities to cause fruit and stem petiole rot. Pathogenicity on fruit was examined by placing a 5 mm plug from five-day-old cultures on surface disinfested fruits, with mock-inoculated (PDA plug only) and non-inoculated controls. Fruit were placed in incubators (~98% RH, 22°C, 10:14 hrs L:D) and arranged in a complete block design with three blocks and five fruit/treatment/block; the study was conducted twice. White hyphae and sclerotia formed on 41 to 53% of fruit inoculated with both isolates, necrotizing fruit within 6 days post inoculation (DPI); Sclerotinia fruit rot did not develop in controls. Pathogenicity on petioles was examined in a replicated study on three-month-old cv. Flavorfest using a petiole inoculation method described in (Peltier and Grau 2008); mock-inoculated stems were placed in sterile PDA. Plants were arranged in the greenhouse (~20-28°C; 12:12 hrs L:D) in a randomized complete block design with three blocks and three plants/treatment. Dark brown necrosis averaging 5.8 ± 0.2 mm in length developed on 100% of plants in both isolate treatments within 3 DPI and by 6 DPI had expanded to 42.1 ± 4.8 mm on average, spreading into the crown on some plants. Necrosis did not extend beyond 2 mm from the cut tip in controls. The pathogen was recovered from surface disinfested tissue for both isolates. In a subsequent study, stem rot susceptibility was compared among four short-day strawberry cultivars common to the region, cvs. Flavorfest, Chandler, Allstar and Honeoye (same method as above). Stem lesions were 2 to 3 times longer on cv. Flavorfest (41.78(ave) ± 6.73(se) mm) compared to all other cultivars (13.68(ave) ± 1.56(se) mm) (P < 0.0001, Tukey's test). To our knowledge, this is the first report of both Sclerotinia fruit and crown rot on strawberries anywhere in the mid-Atlantic region. Our results indicate that cv. Flavorfest, a recently developed cultivar with expanding acreage, may be more susceptible to Sclerotinia. These are both unusual diseases circumglobally, especially Sclerotinia fruit rot (Farr and Rosman 2019, Maas 1998); the new occurrence in this region may be associated with increased use of this cultivar.

Exploring Plant Performance, Fruit Physicochemical Characteristics, Volatile Profiles, and Sensory Properties of Day-Neutral and Short-Day Strawberry Cultivars Grown in Texas.

To assist increasing annual acreage of Texas-grown (U.S.A.) strawberries, it is essential to select cultivars with excellent plant and fruit quality characteristics suitable to the diverse environments. This study assessed multiple traits of 10 strawberry cultivars grown under high tunnels. A significant difference (p ≤ 0.05) was observed for all traits, which possessed a wide variability of metabolites. Plant analysis (number of live plants, plant vigor, and harvest yield) indicated that the yield ranged from 226 to 431 g/plant, positively correlated to plant vigor. Fruit physicochemical characteristic analysis, including red color (absorbance at 500 nm) and taste-associated indicators [°Brix, titratable acidity (TA), and total soluble solids (TSS)/TA], showed that °Brix and TSS/TA ranged from 8.0 to 12.9 and from 9.1 to 15.3, respectively. More than 300 volatiles were identified using solid-phase microextraction-gas chromatography-mass spectrometry, and total volatiles varied 1.5 times with high variance of individual compounds between cultivars. Descriptive sensory analysis indicated that strawberry flavor was positively associated with sensory attributes of sweetness, jammy, fruity, buttery, fresh, and creamy while negatively related to bitterness, astringency, and sourness. Partial least squares regression indicated that strawberry flavor was highly correlated with sweet taste and volatile composition. No specific relationship between these traits and day-neutral or June-bearing varieties was identified. Ideal cultivars for Texas growing conditions with superior and balanced flavor qualities were Albion, Sweet Charlie, Camarosa, Camino Real, and Chandler.

Stolon Development and Cultural Production Practices of Winter-Grown Strawberries

ABSTRACTThe four experiments described here are part of a 5-year program focused on determining whether day-neutral and short-day strawberries would be suitable for commercial off-season/winter (temperate climate) production in greenhouses. All research was performed using container-grown plants fertigated through a capillary mat production system with heat supplied under the benches. The first experiment focused on stolon development. The second experiment investigated the influence of stolon removal on berry production and included the removal of flowers for the first three weeks. The third and fourth experiments were conducted as a comparison of university research (experiment 3) versus a commercial operation (experiment 4). In experiment one, of 13 cultivars, ‘AC Wendy’ plants produced significantly more stolons than the other cultivars. In experiment two, stolon production peaked at weeks 12 and 13, with ‘Chandler’ plants producing significantly more stolons (starting at week 9) than the other cultivars. At week 13, ‘Seascape’ plants produced more total berry weight than the other cultivars. The influence of stolon removal on total berry weight varied, with ‘Evie-2+’ plants (large crowns) producing higher total berry weight with the stolons on as compared to ‘Evie-2’ plants, which produced higher total berry weight with the stolons removed. In experiment 2, fruit production was low and was probably a result of deflowering for three weeks. Consequently, it may not be advisable to deflower during the ‘off-season’ for greenhouse-grown strawberries. In the final two experiments, which involved a commercial cooperator as well as the university greenhouse, it was found that of the five cultivars trialed, the same cultivars at both sites produced the maximum total berry weight. Stolon production differed at the two locations, but the optimal time for stolon removal was similar. Thus, it is recommended that for winter greenhouse production, stolons be removed initially at week 8 and then at weeks 11–12 of the production cycle.

‘Malling Centenary’, a short-day strawberry cultivar from NIAB-EMR

‘Malling Centenary’, a short-day strawberry cultivar from NIAB-EMR

The effect of end of day far-red light on regulating flowering of short-day strawberry (Fragaria × ananassa Duch. сv. Paros) in a long-day situation

The effects of manipulation of phytochrome state and plant age were tested on flowering strawberry (Fragaria × ananassa Duch. cv. Paros) using end of day far red light (EOD-FR) under undesirable environmental conditions (high temperature and long day). The first and second experiments examined the effects of EOD-FR on flower induction, level of phytochrome and carbohydrates (starch, sucrose, fructose, and glucose), which were variable along with acid invertase enzyme. In the first experiment, there was no flower emergence, but in the second experiment, induction occurred in plants exposed to 6 h of EOD-FR for 32 cycles. The third experiment tested the effect of far red light (6 h + 32 d) on plants of 8, 10, and 12 weeks of age, and induction occurred in 12-week-old plants. The results of experiments II and III indicated that in the induced plants, the amount of phytochrome (Pr) increased. Furthermore, a higher level of sucrose was observed in induced plants, but the level of starch was lower. Nevertheless, amounts of glucose, fructose, and invertase enzyme did not change significantly, although they did show a slight increase in induced plants. These results provide evidence that a light-quality pathway exists that acts on regulation of flowering time in short-day strawberry cultivation.

Production and physicochemical characteristics of strawberry cultivars produced in organic cropping system

The conventional production of strawberries has been characterized by high use of inputs resulting in chemical waste in the fruit. Strawberry produced on organic cropping system becomes important, because have more economic autonomy to family farms and reaches levels ecological, social and economic sustainability. The production and physicochemical characteristics of four short-day strawberry plants – Campinas, Chandler Dover and Vila Nova – were evaluated in order to obtain information to the development of organic system productive in the northwestern region of Rio Grande do Sul state, in Brazil. The experiment was conducted between May 1 st and November 3 rd , 2014. As regarded production characteristics, in each productive month and in total accumulated of the cycle were evaluated the mass and the quantity of accessory fruit produced by the plant. The physicochemical characteristics were determined through the soluble solid content, titratable acidity, pH and the color of the accessory fruits. Referring to the productivity, 'Campinas' stood on the other cultivars, showing bigger mass and total accessory fruit number. About the relation of soluble solid content and titratable acidity, the cultivars Chandler and Dover reached the best results, whereas the color of the 'Chandler', 'Campinas' and 'Villa Nova' accessory fruits submitted higher °Hue value.

Light quality regulates flowering in FvFT1/FvTFL1 dependent manner in the woodland strawberry Fragaria vesca.

Control of flowering in the perennial model, the woodland strawberry (Fragaria vesca L.), involves distinct molecular mechanisms that result in contrasting photoperiodic flowering responses and growth cycles in different accessions. The F. vesca homolog of TERMINAL FLOWER1 (FvTFL1) functions as a key floral repressor that causes short-day (SD) requirement of flowering and seasonal flowering habit in the SD strawberry. In contrast, perpetual flowering F. vesca accessions lacking functional FvTFL1 show FLOWERING LOCUS T (FvFT1)-dependent early flowering specifically under long-days (LD). We show here that the end-of-day far-red (FR) and blue (B) light activate the expression of FvFT1 and the F. vesca homolog of SUPPRESSOR OF THE OVEREXPRESSION OF CONSTANS (FvSOC1) in both SD and LD strawberries, whereas low expression levels are detected in red (R) and SD treatments. By using transgenic lines, we demonstrate that FvFT1 advances flowering under FR and B treatments compared to R and SD treatments in the LD strawberry, and that FvSOC1 is specifically needed for the B light response. In the SD strawberry, flowering responses to these light quality treatments are reversed due to up-regulation of the floral repressor FvTFL1 in parallel with FvFT1 and FvSOC1. Our data highlights the central role of FvFT1 in the light quality dependent flower induction in the LD strawberry and demonstrates that FvTFL1 reverses not only photoperiodic requirements but also light quality effects on flower induction in the SD strawberry.

Financial results achieved in short-day strawberry production

In South-western Ontario's continental climate (short days, hot summers and very cold winters) the matted-row system was the dominant production system to grow short-day strawberries. Varieties-staggered production (planting a combination of early, mid and late-season varieties) provides strawberry harvest from five to seven weeks. Short-day strawberries are vegetative grown in the first year, and harvested for two consecutive years. The total cost of short-day strawberry production was 54,370 $CAD/ha. The production and harvest costs in the first and second years were 20,812 $CAD/ha and 16,930 $CAD/ ha, respectively, and accounted for 69.42% of the total. Pre-plans operations were the least expensive procedures costing 8.13%, while planting and care of young plants made up 22.45% of the total costs. The total income of growing short-day strawberries under a matted-row system was 76,671 $CAD/ha (the first and second production years 41,330 $CAD/ha and 35,341 $CAD/ha, respectively). The short-day strawberries in matted-row system, with average yield of 15,722 kg/ha, generated a net revenue of 22,300 $CAD/ha.

NEW METHODS FOR ADVANCING OR DELAYING ANTHESIS IN SHORT-DAY STRAWBERRY

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Berries: From Genomics to Sustainable Production, Quality and Health NEW METHODS FOR ADVANCING OR DELAYING ANTHESIS IN SHORT-DAY STRAWBERRY

‘Puget Crimson’ Strawberry

‘Puget Crimson’ is a new short-day strawberry (Fragaria ·ananassa Duchesne ex Rozier) cultivar jointly released by Washington State University (WSU), Oregon State University, and the U.S. Dept. of Agriculture– Agricultural Research Service (USDA-ARS). ‘Puget Crimson’ has been noted for high yields, very late-season ripening, large size, and excellent fresh flavor. Although suitable for processed uses, fruit of ‘Puget Crimson’ will most likely be used for the fresh market because of its late harvest season and sweet flavor.

Relationships between strawberry fruit quality attributes and crop load

Crop load can influence fruit quality in several horticultural species. The aim of the present study was to determine the effect of different concentrations of calcium on crop quality traits in three short-day strawberry ( Fragaria × ananassa Duch.) cultivars (‘Ventana’, ‘Camarosa’ and ‘Candonga’) and to assess the relationships between crop load and quality parameters. The studies were conducted using a hydroponic system in a greenhouse. Calcium was added as Ca(NO 3) 2 at 2 mM, 3 mM, 4 mM and 5 mM. A completely randomized block design (4 Ca concentrations × 3 cultivars) with three replicates was used. Each replicate consisted of 12 plants grown in polyethylene bags (100 cm × 18 cm × 3 cm) filled with coconut peat. Titratable acidity, total soluble solids and firmness were measured throughout the experimental period. Calcium application had no effect on fruit quality attributes but the genotype effect was clear. At the end of the experiment (28th May, 2008), titratable acidity was positively related to the fresh weight of above-ground biomass and number of leaves respectively in the ‘Ventana’ and ‘Camarosa’ cultivars. Higher values of total soluble solids were found at low crop load in ‘Ventana’ but in ‘Camarosa’ this relation was not found. In ‘Candonga’, higher total soluble solids were linked to crop load. In ‘Ventana’, titratable acidity significantly decreased as crop load increased, and in ‘Camarosa’ high values of titratable acidity were found at different values of crop load. ‘Ventana’ seemed to be more sensitive to the effects of crop load patterns. Genotype was an important factor in determining fruit quality parameters.

Influence of short day treatment on autumn fruit production of June-bearing strawberry cultivars

Short-day (SD) strawberry cultivars were grown in 2008 and 2009 fall each year to evaluate effects of short-day (SD) treatment on flowering and fall fruit production in the high elevation of South Korea. In 2008, daughter plants of six cultivars ‘Maehyang’, ‘Seolhyang’, ‘Keumhyang’ (Korean short-day cultivars), ‘Akihime’, ‘Red pearl’, and ‘Sachinoka’ (Japanese short-day cultivars) were exposed to short-day (10-h photoperiods) conditions at the high elevation (HE, 800 m elevation) for 35 days beginning in late June. On 31 July, plants were removed from the SD environment and established in a substrate system at the highland. In 2009, the ‘Akihime’ and ‘Seolhyang’ were examined again. In 2008, flower bud initiation rate was above 90.0% for all cultivars except for ‘Akihime’ (83.3%). Fruit harvest commenced 1st of October 2008 and average fruit weight was consistently > 20g except for ‘Sachinoka’ (18 g). By mid-November, plants of ‘Seolhyang’ and ‘Akihime’ produced 222–260 more grams of fruit compared to other cultivars, with ‘Seolhyang’ having the earliest production. In 2009 experiment, flower bud initiation rates of ‘Akihime’ and ‘Seolhyang’ plants were 85.4% and 82.4%. Due to the earlier planting in 2009, fruit harvest commenced on 8 September (one month earlier than in 2008) and extended over 10 weeks. Yield and fruit numbers of ‘Akihime’ and ‘Seolhyang’ were 397.7 g, 22.7 and 331.7 g, 19.8, respectively. Results of this study indicate that exposure to SD photoperiods and relatively cool temperatures at HE can increase autumn fruit production in SD strawberry cultivars ‘Akihime’ and ‘Seolhyang’.

Relationship between tipburn and leaf mineral composition in strawberry

Malformation of emerging leaves with distortion of leaf tips, a condition known as tipburn, is frequently observed in strawberry. Calcium (Ca) deficiency has been considered the main cause of tipburn. The aim of the present study was to analyse the relationship between leaf mineral composition and the incidence of tipburn in three short-day strawberry ( Fragaria x ananassa Duch.) cultivars (‘Ventana’, ‘Camarosa’ and ‘Candonga’) submitted to different concentrations of Ca. The studies were conducted in a hydroponic system in a greenhouse. Calcium was added as Ca(NO 3) 2 at 2 mM, 3 mM, 4 mM and 5 mM. A completely randomized block design (4 Ca concentrations × 3 cultivars) with three replications was used. Each replicate consisted of 12 plants grown in a polyethylene bag (100 cm × 18 cm × 3 cm) filled with coconut peat. Crown diameter and tipburn incidence were evaluated throughout the experimental period, and at the end of the experiment leaf mineral composition was assessed. In general, plants with larger crown diameters had a greater incidence of tipburn. The ‘Candonga’ cultivar had the smallest incidence of tipburn, while the ‘Camarosa’ and ‘Ventana’ cultivars were more susceptible. There was no correlation between level of Ca applied and incidence of tipburn. The incidence of tipburn was associated with foliar K:Ca and K:Mg ratios. Ratios above 3.40 for K:Mg and 1.77 for K:Ca represented a risk of more than 50% of tipburn incidence, when overall means for all cultivars and levels of Ca were used.