Southern Highbush Blueberry Cultivars Research Articles

Chemical control of Cylindrocladium and Rhizoctonia root rots in blueberry propagation

Cylindrocladium and Rhizoctonia root rots, caused by Cylindrocladium parasiticum and binucleate Rhizoctonia spp., respectively, are common soilborne diseases observed during blueberry propagation in Georgia, USA. Six trials with artificially inoculated propagation medium were completed in a shade-house to determine the efficacy of select fungicides to control these diseases. For Cylindrocladium root rot, two trials with single-drench fungicide applications were made at the time the cuttings (southern highbush blueberry cultivar Rebel) were stuck. In two additional trials, a second drench application was added two weeks later. In all trials, fludioxonil (Medallion) significantly reduced lesion incidence and lesion length. Neither triflumizole (Terraguard) nor thiophanate-methyl (Cleary's 3336) consistently reduced lesion incidence with one application, indicating that a single application of these materials was not sufficient for disease suppression. The second fungicide application improved disease control for all fungicides. However, fludioxonil always performed statistically better than thiophanate-methyl and numerically better than triflumizole as indicated by lesion incidence, lesion length and girdling incidence. For Rhizoctonia root rot, two trials were completed, each with two fungicide applications (when cuttings were stuck and 2 weeks later). Fludioxonil and azoxystrobin (Heritage) significantly reduced lesion incidence and lesion length in both trials. Flutolanil (Prostar) reduced lesion incidence in both trials and also reduced lesion length in the second trial. Pending labeling for this use pattern, fludioxonil, which has provided good control of both diseases in our trials, may form the basis of a fungicide rotation program to supplement sanitation practices for managing Cylindrocladium and Rhizoctonia root rots in blueberry propagation.

Performance of Southern Highbush Blueberry Cultivars Under High Tunnels in Florida

A study was conducted over two southern highbush blueberry (Vaccinium corymbosum × Vaccinium darrowi) seasons in a grower field in Florida. The objective was to compare the early fruit weight of southern highbush blueberry cultivars in high tunnels and in open fields. Four treatments were tested using combinations of two southern highbush blueberry cultivars (Snow Chaser and Springhigh) and two production systems (open fields and 18-ft-high tunnels). The results indicated that there was a significant effect of the production systems on the number of days with air temperatures at or near freezing (≤34 °F), and maximum and minimum air temperatures. The minimum air temperature in open-field plots reached ≈19 and 21 °F (61 freezing or near-freezing events) in the 2009–10 and 2010–11 seasons, respectively, whereas the minimum air temperatures inside the high tunnels were ≈32 and 33 °F, respectively, during the same seasons (only 3 days at ≤34 °F). This indicated that using high tunnels was an effective means to avoid freezing air temperatures in blueberries. In the first season, the cumulative early fruit weight was the highest in plots planted with ‘Snow Chaser’ inside the high tunnels (≈10 tons/acre), while the combined production of the two cultivars in the open fields did not reach 1 ton/acre until the end of the early harvests. The following year, there were no differences in the cumulative early fruit weight of both cultivars when planted in the open fields (2.2 tons/acre) and the cumulative fruit yields of ‘Springhigh’ and ‘Snow Chaser’ growing inside the high tunnels was twice and four times higher, respectively, than the early fruit production obtained in the open fields. These data showed the profound effect of high tunnels on flower protection and fruit set. High tunnels reduced water use for freeze protection. The total volume used in the open fields during the freezing or near-freezing days was ≈2.5 acre-inch/acre per 8 hours of freeze protection, whereas only 1/10 of that volume was applied inside the structures.

Effects of Southern Highbush Blueberry Cultivar and Treatment Threshold on Flower Thrips Populations

In Florida, southern highbush (SHB) blueberries (Vaccinium corymbosum L. x Vaccinium darrowi Camp) are grown for a highly profitable early season fresh market. Flower thrips are the key pest of SHB blueberries, and Frankliniella bispinosa (Morgan) is the most common species found. Flower thrips injure blueberry flowers by feeding and ovipositing in all developing tissues. These injuries can lead to scarring of developing fruit. The objectives of this study were to determine the relationship between thrips and yield in different SHB blueberry cultivars and to determine an action threshold. Experiments were conducted during early spring 2007 and 2008 on four farms; a research farm in Citra, FL; and three commercial farms, two in Hernando Co., FL., and one in Lake Co., FL. At the Citra farm, 'Emerald', 'Jewel', 'Millennia', and 'Star' blueberries were compared in 2007, and all but Star were compared in 2008. On the Hernando and Lake Co. farms, two treatment thresholds (100 and 200 thrips per trap) and an untreated control and four cultivars (Emerald, Jewel, Millennia, and 'Windsor') were compared. Emerald consistently had more thrips per trap and per flower than the other cultivars on all four farms. However, this did not always lead to an increase in fruit injury. Thrips numbers exceeded the threshold on only one farm in 2007, and there was a significantly lower proportion of injured and malformed fruit in the 100 thrips per trap threshold treatment compared with the control on this farm.

Overexpression of a blueberry-derived CBF gene enhances cold tolerance in a southern highbush blueberry cultivar

Blueberry cultivars are subject to freezing damage in the winter and early spring. C-repeat binding factor (CBF) genes are transcription factors known to induce the expression of genes associated with cold acclimation and freezing tolerance. A CBF-encoding gene (BB-CBF) was isolated from the northern highbush blueberry Bluecrop (a cold-tolerant cultivar) and introduced into the southern highbush blueberry Legacy (a more cold-sensitive cultivar) to determine the effects on cold tolerance. The BB-CBF coding sequence was linked to the cauliflower mosaic virus 35S promoter and the 35S polyA terminator and was subsequently introduced into Legacy using Agrobacterium-mediated transformation of leaf explants. Fifty-seven transgenic events were obtained. Non-acclimated mature leaves, dormant flower buds, and flowers at various developmental stages from transformants and nontransgenic plants were subjected to electrolyte leakage assays over the course of 3 years, 2009–2011. Transgenic lines showed an increase in freezing tolerance in leaves and dormant buds. Expression of putative downstream components of the blueberry CBF regulon was increased in non-acclimated transgenic lines, and, in some cases, to a level similar to that of acclimated control plants. Following low temperature exposure, BB-CBF-overexpressing transgenics and controls expressed these genes at similar levels.

Settling behavior of the glassy‐winged sharpshooter, Homalodisca vitripennis, vector of Xylella fastidiosa, on southern highbush blueberry cultivars

AbstractThe xylem‐limited bacterium Xylella fastidiosa Wells, Raju, Hung, Wiseberg, Mandelico‐Paul & Brenner causes bacterial leaf scorch, a new disease of southern highbush blueberry [Vaccinium corymbosum L. (Ericaceae) interspecific hybrids] in the southeastern USA. The bacterium is transmitted by sharpshooter leafhoppers (Hemiptera: Cicadellidae), with the glassy‐winged sharpshooter (GWSS), Homalodisca vitripennis (Germar), being the most common potential vector in blueberry plantings. Considerable differences are observed in disease intensity among blueberry cultivars in the field, but it remains unknown whether these differences are due to variations in cultivar susceptibility to the bacterium, differences in attractiveness to its vector(s), or both. The settling and feeding behavior of GWSS was evaluated on three southern highbush blueberry cultivars (FL 86‐19, Star, and Emerald) in the greenhouse; in previous field studies, these cultivars were found to be affected by bacterial leaf scorch at high, moderate, and low levels, respectively. Potted plants were caged together with field‐collected GWSS adults for a period of 5 days, with either all three cultivars caged simultaneously (choice test) or individually (no‐choice test). In the choice tests, no differences in cultivar attractiveness were observed during the first 2 days of study. However, from the 3rd day, significantly more adults settled on Emerald (52.7%) than on Star (25.5%) and FL 86‐19 (17.7%). In contrast, in no‐choice tests, the overall host plant acceptance for the three cultivars was similar, and 89.3–92.1% of adults settled on these plants. A significantly greater number of adults settled on the stems (79.3%) vs. the leaves (11.2%). Moreover, they preferred the middle portion of the shoot (56.9%) compared with the upper (7.8%) and the lower (14.7%) portions. In a separate study on FL 86‐19, greater numbers of GWSS nymphs settled on the upper (actively growing) portion of the shoot (82.3%), whereas only 15.8 and 1.5% settled on the middle and lower portions, respectively.

‘Gupton’ Southern Highbush Blueberry

Southern highbush blueberries (Vaccinium sp.) are hybrids derived from crosses between the (northern) highbush blueberry (V. corymbosum) and germplasm developed from Vaccinium spp. that is both native and adapted to the southeastern United States. Southern highbush blueberries have an advantage over rabbiteye blueberries, the predominant type grown in the region, as a result of their earlier ripening period. As a result, blueberry growers in the southern United States, and additional regions having relatively mild winters, have greater opportunities to capitalize on the lucrative early U.S. fresh berry market because the supply of fresh market berries from the southern hemisphere diminishes concurrently with their ripening in the United States. ‘Gupton’ is a new southern highbush blueberry (Vaccinium hybrid) released by the U.S. Department of Agriculture’s Agricultural Research Service (USDA-ARS). ‘Gupton’ is a productive and relatively early-ripening southern highbush blueberry cultivar that possesses favorable fruit quality attributes including large berries containing high soluble solids content and have excellent flavor and firmness, light blue color, and good resistance to raininduced physiological splitting that is expected to perform well in the gulf coast region and other areas of the United States where southern highbush blueberries are grown.

Fruit Development Period of Several Southern Highbush Blueberry Cultivars

Flowering and ripening times were recorded for the southern highbush blueberry (Vaccinium corymbosum) cultivars Emerald, O'Neal, and Star, along with the newer University of Georgia releases ‘Camellia’, ‘Rebel’, ‘Southern Splendour’, and ‘Suziblue’ over several years at three locations in Georgia. Nearby weather stations were utilized to record temperatures for calculating chill hours and heat units during each of the years. These data were used to calculate fruit development period for the different cultivars as a function of real time (days) and thermal time (heat units). Depending on cultivar and chill hours at a location, flowering time varied as much as 29 days from year to year. Overall, ‘Emerald’ was the earliest flowering, followed by ‘Rebel’. ‘Camellia’ was the latest to flower among the cultivars. Average fruit development period for the cultivars were: Southern Splendour, 56.2 days; Rebel, 65.3 days; Suziblue, 65.5 days; Star, 67.1 days; Camellia, 68.8 days; O'Neal, 71.9 days; and Emerald, 82.8 days. The shortened fruit development period of ‘Southern Splendour’ resulted in a ripening time similar to ‘Rebel’ and ‘Star’, even though flowering time of ‘Southern Splendour’ was often several days later. Using heat units instead of days did not greatly reduce the coefficient of variation associated with fruit development period. However, the mean absolute and maximum difference between observed and predicted time to ripening was improved for most cultivars when heat units were used. These data should be useful in estimating how these blueberry cultivars will perform under diverse environments.

Survival of Southern Highbush Blueberry Cultivars in Phytophthora Root Rot-Infested Fields in South Mississippi

Phytophthora root rot is an important disease of commercial blueberries and is most severe when blueberries are grown in wet soils with poor drainage. Symptoms include small, yellow or red leaves, lack of new growth, root necrosis, and a smaller root system than healthy plants. Four studies were conducted in south Mississippi to evaluate the effect of bed height and soil amendment on the survival of 19 southern highbush blueberry cultivars transplanted into fields infested with the root rot pathogen, Phytophthora cinnamomi. Plants were rated twice a year for overall vigor on a scale of 0 = plant dead to 5 = most vigorous. The most vigorous cultivars were: ‘Southmoon’ in the 2005 study, ‘Gulfcoast’ in the 2006 study, and ‘Springhigh’ in the 2008 study. In the 2005 and 2006 studies, plants grown on raised beds were more vigorous than those grown on flat beds and those grown in soils amended with peat moss were more vigorous than those grown in soils with no amendment. In the 2008 study, plants grown in soil amended with pine bark were more vigorous than those grown in soil amended with peat moss. However, plant vigor declined each year, and most plants died within 3 years of planting whether they were planted on raised or flat beds and whether they received any soil amendments or not. No cultivar thrived in any planting. These studies demonstrate that southern highbush blueberries should not be planted in soils known to be infested with P. cinnamomi.

Microsatellite Markers: Valuable in Vaccinium L.

The United States Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository, Corvallis, Oregon, maintains a collection of Vaccinium L. that contains >1,700 accessions representing 66 species from 33 countries. The mission of the National Clonal Germplasm Repository is to acquire, preserve, evaluate, document, and freely distribute crop germplasm. Microsatellite (syn. simple sequence repeat) markers provide a unique fingerprint for identifying germplasm accessions and are useful for genetic diversity analysis and in saturating genetic maps. The National Clonal Germplasm Repository Genetics Lab was the first to develop 39 simple sequence repeat primer pairs from expressed sequence tags and 10 simple sequence repeat primer pairs from a genomic microsatellite-enriched library of ‘Bluecrop’. Simple sequence repeat markers from these 49 primer pairs were identified for providing unique fingerprints for blueberry, cranberry, and ohelo berry; evaluating genetic diversity of wild and cultivated blueberry and southern highbush blueberry cultivars; assessing the effect of wide hybridization on genetic diversity and heterozygosity of the cultivated blueberry; populating the diploid Fl #10 (Fla4B x W85-20) x W85-23 and the tetraploid ‘Draper’ x ‘Jewel’ linkage maps; supplying a source of useful markers in 22 species representing nine Vaccinium sections; and use in population genetic analyses in diploid Vaccinium section Myrtillus taxa, such as V. calycinum, V. reticulatum, V. scoparium, and V. praestans. Over 450 simple sequence repeat primer pairs were recently designed from newly generated blueberry expressed sequence tags as part of a Specialty Crop Research Initiative project to develop genomic tools for blueberry, and will provide a valuable resource for the Vaccinium research and breeding community.

Recent Advances in Blueberry Transformation

Although Vaccinium cultivars have been generated exclusively through the traditional methods of controlled hybridization and deliberate selection, genetic transformation could provide a powerful approach to supplement conventional breeding methods for Vaccinium by introducing genes of interest. A reliable transformation system depends on efficient plant regeneration, reliable gene delivery, and effective selection. To date, in blueberry, adventitious shoot regeneration using leaf explants has been the most desirable regeneration system; Agrobacterium-mediated transformation is the major gene delivery method; and effective selection has been reported using either the nptII or the bar gene as selectable markers. In 2004, stable transformation was reported for four highbush blueberry cultivars, with a transformation frequency ranging from 5.0–15.3%. In 2006, the first field trial of transgenic blueberry with herbicide resistance was performed. In 2009, a blueberry C-repeat binding factor (CBF) gene (GenBank AF234316) was transformed into a southern highbush blueberry cultivar Legacy in order to improve cold tolerance by elucidating the CBF-regulated network in blueberry. This progress has demonstrated that blueberries can be improved through genetic engineering. In the future, as more genomic resources for Vaccinium become available, more genes of interest will be identified and isolated. Genetic transformation will allow us to evaluate these genes as to their functions. Currently, there is industry-wide concern about the application of transformation technology in blueberries, even though numerous transgenic crops have been deployed. Hopefully, new engineering strategies, such as intragenic transformation, RNAi, and marker-free technologies, will reduce public concerns about transgenic Vaccinium plants.

Volatile Composition of Four Southern Highbush Blueberry Cultivars and Effect of Growing Location and Harvest Date

The volatile composition of four southern highbush blueberry cultivars ('Primadonna', 'Jewel', 'Snowchaser', and 'FL02-40') grown in two locations (Gainesville and Haines City, FL) and harvested multiple times was investigated. A total of 42 volatiles were identified, including 8 esters, 12 terpenoids, 11 aldehydes, 7 alcohols, and 4 ketones. Twelve of these volatiles are reported for the first time in highbush blueberries, with 10 being positively identified: (Z)-3-hexenal, (E,E)-2,4-hexadienal, (E,Z)-2,6-nonadienal, (E,E)-2,4-nonedienal, methyl 2-methylbutanoate, butyl acetate, 2-methylbutyl acetate, and geranyl acetate. The dominant volatiles were aldehydes followed by terpenoids and esters, with distinct varietal profiles. 'Primadonna' was characterized by a large amount of esters and C-6 aldehydes. In contrast, fewer than 4 esters were found in 'FL02-40' and 'Snowchaser', respectively, but they produced more terpenoids than 'Primadonna' and 'Jewel'. Location and/or harvest date affected the production of volatiles in 'Primadonna', but not so much in the other cultivars.

HYDROGEN CYANAMIDE ON BUDBREAK AND YIELD OF 'O'NEAL' HIGHBUSH BLUEBERRY IN SOUTH URUGUAY

Southern Highbush Blueberry cultivars are becoming a high value crop in Uruguay since 2002. A rapid increase in surface area is due to the good prices of blueberries at the beginning of the off-season fresh market. The application of Hydrogen Cyanamide (Dormex, H 2 CN 2 ,) in our mild and variable winter is one of the cultural practices that may improve yields and advance harvest. This study was conducted in two commercial blueberry orchards in the south of Uruguay (34°44' south latitude). 'O'Neal' (V. corymbosum L. hybrid) plants were sprayed with 0, 1, 1.5 or 2% of Dormex (v/v) at two moments in (May and June). The experiments had a randomized complete block design with 6 plants per treatment with 3 replications in 2005 and 6 replications in 2006. Variables measured were: total length plant, nodes number per plant, reproductive and vegetative budbreak, fruit number and total fruit weight (picked up twice per week in harvest). June applications of H 2 CN 2 accelerated vegetative and reproductive budbreak in both evaluated years, advancing fruit ripening. Dormex, the H 2 CN 2 applied at 1%, increased by 13,2% and 8% the total kg/plant harvested in the first 10 days in 2005 and 2006 respectively. However, Dormex at the 2% H 2 CN 2 sprayed in June injured apical flower buds mainly at stages 2 and 3. This removal of the apical dominance stimulated growth of lateral vegetative buds one month earlier than the control. Even though the final number of vegetative budbreak was higher, the fruit weight was improved only on the first harvest date. The effect on fruit number and total harvest weight were influenced by Dormex treatment depending on the doses and chill hours accumulated at each date of application moment.

Adventitious shoot regeneration from leaf explants of southern highbush blueberry cultivars

Protocols were developed to optimize adventitious shoot regeneration from four southern highbush blueberry cultivars. Leaf explants from 6 week-old shoots of the four cultivars were excised and cultured on woody plant medium each containing thidiazuron (4.54 or 9.08 μM), zeatin (18.2 μM), or zeatin riboside (5.7 or 11.4 μM) either separately or in combination with α-naphthaleneacetic acid at 2.69 μM. Optimum medium for shoot regeneration was genotype-dependent. Efficient regeneration was obtained at frequencies of 88.9% for ‘Jewel’, 87.8% for ‘Emerald’, 53.3% for ‘Jubilee’ and 87.8% for ‘Biloxi’. Leaf explants of newly developed shoots from the cultures having undergone five subcultures had higher regeneration frequencies than those having undergone two subcultures. Regenerated shoots, 80–100% for each cultivar, rooted in 8 weeks after transplantation to soil. The regeneration systems described have potential use in genetic transformation of southern highbush blueberry cultivars.

Southern Highbush Blueberry Production in High Tunnels: Temperatures, Development, Yield, and Fruit Quality During the Establishment Years

Growers interested in producing early, high-quality, southern highbush blueberries (Vaccinium corymbosum L.) in high tunnels face a lack of information regarding appropriate cultural methods. We sought to elucidate the optimal date to close high tunnels to hasten vegetative and reproductive growth of organic southern highbush blueberry cultivars Emerald and Jewel grown in Georgia. The three dates selected to close the high tunnels were 15 Dec., 2 Jan., and 16 Jan. High tunnels raised soil and daytime air temperatures during winter months, but the tunnels did not retain heat at night and did not provide freeze protection without the use of propane heaters. The high tunnel microclimate advanced both vegetative and reproductive growth compared with outdoor plants. Averaged over the 2-year study, the 15 Dec. tunnel closure advanced flower initiation by 38 days for ‘Emerald’ and 39 days for ‘Jewel’ compared with outdoor control plants. Synchronization of flowering of the two cultivars was poor in 2007 when ‘Emerald’ flowered much earlier than ‘Jewel’ and much better in 2008. In 2007, flower and fruit development of ‘Jewel’ were faster than that of ‘Emerald’ with Jewel going from the appearance of individual flowers to ripe fruit in 80 days as compared with 105 days for ‘Emerald’. Total yield was strongly correlated with fruit set (r = 0.94). ‘Emerald’ fruit contained higher concentrations of soluble solids and anthocyanins than ‘Jewel’ fruit, and anthocyanin concentrations increased throughout the harvest period. No fruit matured in 2008 as a result of freeze damage. The biggest obstacle for high tunnel production of southern highbush blueberries appears to be preventing freeze damage and assuring pollination. Cost-effective freeze protection and ways to promote good fruit set will be critical to successful production of early southern highbush blueberries in high tunnels.

Production and Identification of Colchicine-derived Tetraploid Vaccinium darrowii and Its Use in Breeding

In Vaccinium L., most tetraploid hybrids between tetraploid cultivated highbush blueberry (V. corymbosum L.) and diploid darrow's evergreen blueberry (V. darrowii Camp) have been produced by exploiting V. darrowii's tendency to produce 2n gametes and a strong triploid block, which greatly reduces the number of triploid hybrids produced. Colchicine-derived tetraploids offer an alternative method of producing V. darrowii plants that will easily cross with tetraploid Vaccinium species. V. darrowii (2n = 2x = 24) seeds were imbibed in 0.2% aqueous colchicine solution for 24 h. The seeds were germinated and seedlings whose morphology suggested colchicine effects were selected at various stages of development. No macromorphological changes were consistently associated with chromosome doubling. However, stomatal guard cells and pollen size increased substantially as a result of chromosome doubling. Several types of plants were identified after colchicine treatment: 1) plants with a doubled LI (epidermal tissues) and LII (internal tissues) plant layers; 2) periclinal chimeras with a doubled LI layer and a normal LII; and 3) periclinal chimeras with a doubled LII layer and a normal LI. Of ≈4000 seedlings that emerged from colchicine-treated seeds, 200 were selected for further examination based on leaf and stem morphology. Of the 200, five appeared to be tetraploid in LI, LII, or both layers based on stomatal guard cell size and pollen size. Crosses between colchicine-derived V. darrowii (4x) plants and southern highbush blueberry (V. corymbosum) cultivars (4x) were successful compared with 4x–2x and 2x–4x crosses using diploid V. darrowii and tetraploid southern highbush blueberry. Stomatal guard cells and pollen screening of the colchicine-treated plants were used as indicators of doubled V. darrowii plants and periclinal chimeras. The results from the crosses between colchicine-treated V. darrowii plants and tetraploid highbush blueberry cultivars confirmed the information obtained by stomata and pollen screening.

Interspecific Crosses and Backcrosses between Diploid Vaccinium darrowii and Tetraploid Southern Highbush Blueberry

Diploid Vaccinium darrowii Camp has been used in breeding tetraploid southern highbush blueberry (Vaccinium corymbosum L.) as a source of reduced chilling requirement, adaptation to hot, wet summers, and resistance to leaf diseases. V. darrowii in Florida is quite variable, but most crosses have involved only one V. darrowii clone, Fla. 4B. The use in breeding of a wider range of V. darrowii accessions would provide beneficial diversity in the blueberry cultivated gene pool. The purpose of this research was to determine the functional 2n gamete frequency of numerous V. darrowii genotypes when crossed with tetraploid V. corymbosum, and to study the pollen fertility and backcross ability of the interspecific (V. darrowii × V. corymbosum) hybrids to V. corymbosum. Crosses between diploid V. darrowii and tetraploid highbush blueberry cultivars had low fruit set compared with the V. darrowii × V. darrowii and highbush × highbush crosses. The unusually high number of hybrids per pollinated flower (HPF) in certain 4x-2x or 2x-4x crosses was attributed to high functional 2n gamete production in certain V. darrowii genotypes. Diploid Vaccinium fuscatum Aiton and diploid V. darrowii × V. fuscatum hybrids, when crossed with southern highbush blueberry cultivars, were equally productive of hybrids whether used as male or female parents. Variation in frequency of functional 2n gametes in V. darrowii, expressed as high HPF, was present within plants (megaspores vs. microspores) and among V. darrowii plants. Of the 114 interspecific (V. darrowii × V. corymbosum) hybrids studied, 106 had pollen stainability >50%. This indicated that most of these hybrids were tetraploid, because triploid blueberries, like most triploid plants, are highly sterile. Twenty-two V. darrowii × V. corymbosum hybrids were backcrossed to tetraploid highbush blueberry cultivars. Fruit set was variable, but large populations of vigorous hybrids were obtained. Lower fruit set was associated with hybrids that had lower pollen fertility. It should be possible to obtain plants of cultivar quality in a few generations of backcrosses.

Fruit quality parameters of some southern highbush blueberries (Vaccinium xcorymbosum L.) grown in Andalusia (Spain)

Physical and chemical parameters of fresh berries from three southern highbush ("O'Neal", "Sharpblue" and "Misty") blueberry cultivars grown in Huelva (Southwestern Spain) under two production systems were measured and evaluated. ANOVA applied to data yielded significant differences between production systems for mean fruit size and mean fruit fresh weight (P

San Joaquin Valley blueberries evaluated for quality attributes

Blueberry production in California was estimated in 2007 at around 4,500 acres and is rapidly increasing. Common southern highbush cultivars with low chilling-hour requirements are being grown from Fresno County southward, including ‘Misty’, ‘O'Neal’, ‘Emerald’, ‘Jewel’, ‘Star’ and others. We characterized the quality parameters (soluble solids concentration, titratable acidity, ratio of soluble solids concentration to titratable acidity, firmness and antioxidant capacity) of six southern highbush blueberry cultivars grown at the UC Kearney Agricultural Center in Parlier, in the San Joaquin Valley, for three seasons (2005-2007). We also conducted in-store tests to evaluate their acceptance by consumers who eat fresh blueberries. We found that the southern blueberry cultivars currently grown under warm San Joaquin Valley conditions are producing blueberry fruit that is of acceptable quality to consumers and profitable to growers.

Occurrence and Prevalence of Foliar Diseases on Blueberry in Georgia

Qualitative and quantitative information about the occurrence and prevalence of fungal species causing foliar diseases on blueberry in the southeastern United States is limited. To close this knowledge gap, a field survey was conducted in 2002 and 2003 involving a total of 177 samples (cultivar-site-year combinations) from plantings of rabbiteye and southern highbush blueberry cultivars in Georgia. Among eight cultivars, Powderblue was the least affected cultivar whereas Star had high foliar disease levels in both years. Averaged by cultivar and year, there was a significant positive correlation between defoliation and disease severity. Septoria leaf spot and Gloeosporium leaf spot were the most prevalent and most severe foliar diseases, occurring on > 30% of samples in both years. Pestalotia leaf spot, Phyllosticta leaf spot, and leaf rust occurred at intermediate prevalence levels. Among these three diseases, leaf rust was most severe (especially in 2003) whereas Pestalotia leaf spot was associated with secondary infections and occurred mostly on southern highbush cultivars. Algal leaf spot and powdery mildew occurred infrequently and inconsistently. More than 70% of leaf samples, especially from the rabbiteye cultivars, showed symptoms of non-pathogenic leaf damage. The foliar disease complex on blueberry in Georgia is considerably more diverse than previously appreciated. Accepted for publication 31 January 2008. Published 21 April 2008.

Efficient in vitro regeneration systems for Vaccinium species

Efficient protocols for shoot regeneration from leaf explants suitable for micropropagation as well as for the development of transgenic plants were developed for blueberry (Vaccinium corymbosum) and lingonberry (Vaccinium vitis-idaea) cultivars. Nodal segments were used to initiate in vitro shoot cultures of lingonberry cultivar ‘Red Pearl’ and southern highbush blueberry cultivar ‘Ozarkblue’. In order to develop an optimized regeneration procedure, different types and concentrations of plant growth regulators were tested to induce adventitious shoot regeneration on excised leaves from micropropagated shoots of both cultivars. The effect on percentage regeneration and number of shoots per explant was investigated. Results indicated that zeatin was superior to TDZ and meta-topolin in promoting adventitious shoot formation. A concentration of 20 μM zeatin was most effective in promoting shoot regeneration in both cultivars, in case of ‘Red Pearl’ along with 1 μM NAA. Shoots were either allowed to root in vitro on medium containing IBA or NAA or ex vitro in a fog tunnel. IBA was superior to NAA for induction of root development in vitro in both Vaccinium cultivars. Ex vitro rooting under high humidity was tested with cuttings from mature field-grown plants, from acclimatized tissue culture derived plants and with unrooted in vitro proliferated shoots planted directly. It was found that in vitro shoots rooted better under fog than cuttings from the other plant sources and rooting was equivalent to that achieved in vitro.