Cultivars can be combined with early,mid, and late season ripening to extend the harvest season over 6 to 8 weeks.The intended method of harvest also affects cultivar selection, such as mechanical harvesting or hand harvesting . For mechanical harvesting, plants should exhibit concentrated ripening periods, moderate vigor, a moderate number of narrowly upright canes , a large number of flower buds and canes, a high resistance to wound pathogens, small to moderate fruit size, a light blue color,small scars, loose fruit clusters, moderate ease of fruit removal, crisp flesh texture,a firm berry, tough/elastic skin, and desirable sugar/acid ratio to assure extended shelf life . According to Ne Smith et al . , “Climax” is considered the standard in Georgia for mechanically harvested blueberries for the fresh market. It has an upright form, narrow crown, and a concentrated harvest . When compared to blueberry crops harvested by commercial hand-pickers,Van Dalfsen found mechanical harvesters had a reduction in yield of 14 to16%, and roughly ten times as many immature berries.Historically, high yield and firmness to withstand shipping were the primary characteristics selected for, but over the past two decades fresh blueberry consumption has increased, leading to emphasis on other qualities such as berry size, increased shelf life, and increased berry quality .
Fresh blueberries are being shipped longer distances as blueberry gains popularity, causing an increase in demand for fruit that are of high quality, reduced softening, and increased shelf life . Marketing of rabbiteyes in the southern states ranges from 90%local sales in South Carolina to 95% shipping in Georgia . Berry size and quality are extremely important for fresh market blueberries, flower pot and firm varieties are well-suited for long-distance shipping . Crops grown for farmers’ markets need to be of very high quality, but firmness for shipping is not as much of a concern .Firmness is one of the key factors analyzed for cultivar selection , and rabbiteye blueberries are more firm than those of northern high bush or the evergreen blueberry. Cultivars with softer berries will often bruise if they are harvested mechanically and do not withstand ship ping well.Machine harvested berries have been found to be softer and show a higher incidence of post harvest decay than hand harvested berries due to damage from the machine harvester . As farms and farm cooperatives continue to grow in size with large plantings and shipping distances increase, firmer rabbiteye fruits will be needed for mechanical harvesting and shipping . Marshall et al . showed that when breeding efforts are aimed at producing firmer fruits, cultivars may be selected that are susceptible to rain induced cracking, as firmer varieties tend to have more susceptibility to cracking. Cultivars should be screened for both firmness and susceptibility to cracking .The quality of fresh fruit is usually indicated by four major aspects: visual quality ; organoleptic quality ; nutritional quality and hygienic quality.
Fruit size is among the most important traits for the fresh blueberry market, but cultivars that consistently produce large berries over multiple harvests are needed . In a study comparing sensory and instrumental qualities of blueberries, Saftner et al . found that sensory scores for appearance were best correlated with berry size. In other words, consumers prefer larger berries. The sensory qualities, such as berry size, color, size, and taste are likely the most influential factor on blueberry preference in farmers’ markets .Customers of farmers’ markets expect higher quality produce, but are also willing to pay premium prices .Berry color is an important factor of fruit quality, and deep-blue berries with a waxy coat, producing a light-blue berry tend to be the most desirable.Blueberries are deep purple to black, but the berries are covered by a glaucous covering, giving blueberries their bluish color . Berry color is affected by both the total anthocyanin content coupled with the quantity and structure of the waxy coating and is a highly complicated attribute . The color is highly influenced by the state of the epicuticular wax found on the berries and the presence of rodlet wax structures, which are responsible for the light blue color found on some blueberries . Generally, the lack of a waxy bloom is an indicator of post-harvest mishandling or overripe berries .A blueberry’s taste is a component of several factors, particularly the aromaticvolatiles, SSC, TA, and the SSC/TA ratio . It is difficult to accurately rate flavor, but blueberries should have a good balance of sugar to acid with a good aftertaste.
The tangy taste in blueberry is due partially to the tartness whichcounter balances the sweetness . Austin and Bondari determined that high soluble solids content with low acid tended to be a pleasant tasting berry, but that low total acid negatively affects storage capacity. Soluble solids, pH, and SSC/TA ratio have been shown to be correlated with berry deterioration, but the SSC/TA ratio is the best indicator . Rabbiteye blueberries are tart when they first turn blue, and often get a negative image in the marketplace because fruit are often picked at this stage . Berry maturity at harvest is one of the main factors affecting storage life and berry quality, as berries do not continue to ripen after harvest. Ultimately there must be a compromise between ensuring the optimum eating quality and providing the flexibility needed for marketing as well as transportation .Rabbiteye blueberries tend to be more resistant than high bush to post harvest decay, and they also typically have a smaller, dry picking scar . This scar is considered to be the primary path of entry for post harvest decay organisms, thus a small, hydroponic grow system dry picking scar is a desirable fruit characteristic. Large berries with small, dry picking scars are the most desirable, but cultivars that produce larger berries often produce larger picking scars .This study is aimed to evaluate the performance of 11 new releases and well-established rabbiteye blueberry cultivars in North Alabama. Science-based cultivar evaluation will help growers select the best suited blueberry cultivars for their growing location and targeted market, to sustain blueberry production, and can lead to increased profits. There is limited information available on blueberry cultivar performance in Alabama and particularly in North Alabama. A study by Dozier et al . conducted nearly two decades ago in southern Alabama evaluated several rabbiteye cultivars, but information is lacking on the performanceof newly released rabbiteye cultivars in various locations throughout the state.Our objective in this study is to evaluate the vegetative growth and development,yield potential, and fruit quality of newly released and well-established rabbiteye blueberry cultivars for their performance in Alabama. Flower bud density was determined as a number of flower buds per cane cross sectional area in 2009. The diameters of 2 canes per bush, with a diameter between 1.0 and 3.0 cm, were measured and flagged, and the number of flowers was counted on each cane.
Flower bud density was expressed by the number of flower buds per unit cross sectional area. Due to an increase in plant size and crop load, this method was not feasible in the 2010 season, when fruit set was determined by flagging 2 fruiting shoots of a similar size on each bush. The length of the fruiting shoot was measured and the fruit were counted. The shoot length was divided by the number of fruit set in order to determine the number of fruit per unit fruiting shoot. To obtain the initial fruit set, data was collected in May, and then the same shoots were counted again just before harvest in late June to determine the final fruit set.Experimental bushes were hand-harvested on a weekly basis, starting when approximately 50% of the berries on the bush were fully colored, and bushes without a significant number of ripe berries were not harvested. Yield data were recorded on each harvest date for each experimental plant. In addition to determining the average yield per bush per harvest, the average total yields per bush were determined across both seasons.Berry sub samples were collected from each harvested bush to determine cultivar fruit qualities characteristics. Berries were placed in a cooler and kept at4˚C before analysis. A 20 g sub sample from each plant harvested was stored at−80˚C for later determination of soluble solids content , titratable acidity, and pH.The fruit quality analysis was performed by measuring berry surface color,average fruit weight, firmness, number of berries with wet scar, berry dry weight,soluble solids content , titratable acidity , the SSC/TA ratio, and pH.The average berry weight was determined on a 50 berry sub-sample/bush. Fruit firmness was determined on a 10 berry sub-sample/bush using a handheld FT 02penetrometer using a 1.5 mm probe. Accordingto NeSmith berries that have firmness exceeding 175 g/mm are likely a good threshold for berries that are suitable for mechanical harvesting.Fruit were held stationary between the thumb and index finger on a flat surface,and the probe was pressed against the fruit in a slow and steady motion until the erry was pierced. The percentage of berries with wet picking scar was determined by examining a 50 berry sub-sample per bush. Berry dry weight was determined by drying 10 berry sub-sample/bush at 77˚C in a Grieve model sc-350oven for 36 hours, and then the berry weight was recorded.SSC, TA, and pH were determined using a method described by Vinson et al .. SSC was determined by first pureeing approximately 20 g of frozen fruit and20 ml of HPLC water, obtained from a Millipore Direct-Q 5 filter system , using a ceramic mortar and pestle into a homogeneous liquid . The resulting liquid was analyzed using a digital refractometer to determine the % SSC at room temperature. To determine TA, the homogeneous liquid was clarified with a centrifuge at 15,000 gn at4◦C for 20 minutes , and the supernatant was filtered with double-layered cheese cloth. The resulting supernatant was brought to a final volume of 40 mL with HPLC water and thoroughly mixed. Five mL of supernatant were diluted to a final volume of 30 mL with HPLC water, which was used to determine TA with an automated titrimeter . The titrimeter was maintained at 10◦C in a Fisher Scientific refrigerated chromatography chamber . A 0.1 M solution of NaOH was titrated to an end point ofpH 8.1. The results were expressed as citric acid equivalent through the following formula: . SSC: TA ratio was determined by dividing SSC by TA. The titrimeter also determines the pH of the sample used to determine the TA . Cultivar vegetative characteristics were evaluated by determining leaf area,chlorophyll readings, and plant growth index.
Average leaf area was based on a30 leaf sample per bush collected late summer and measured with a LicorLI-3100 area meter . Mature leaves located at least 5 nodes away from the terminal bud were used. Chlorophyll readings were taken on 10leaves per experimental bush. Mature leaves located at least 5 nodes back from the terminal bud were used. Bush heights, as well as the plant width measured perpendicularly and diagonally to the planting row were measured to determine plant growth index of each experimental plant. Phosphorus deficiency contributes to reduced yield potential of dry bean. The most pronounced effect of P deficiency on plant growth is reduced leaf size, and increased root growth . Accordingly, phosphorus deficiency in dry bean decreases shoot to root biomass ratio but has no effect on the rate of photosynthesis per unit leaf area .Often P is limiting in tropical soils due to low pH of the soils and high P fixation capacity. Correcting P deficiency is possible through organic or inorganic fertilizer inputs . While applying inorganic fertilizers at low rates can be cost-effective, crop response is often hampered by high P fixation in the soil.