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Sixty-eight highbush blueberry (Vaccinium corymbosum L.) cultivars and selections were evaluated over 3 years for their resistance to the fruit infection phase of mummy berry disease [Monilinia vaccinii-corymbosi (Reade) Honey]. Average incidence of fruit infection under test conditions was 34.3% in 1995, 14.4% in 1996, and 27.9% in 1997, with significant differences occurring among clones in all 3 test years. Several cultivars exhibited consistent resistance to mummy berry fruit infection across all years of testing. `Northsky', `Reka', `Northblue', `Cape Fear', `Bluegold', `Puru', and `Bluejay' were among the most resistant, and `Atlantic', `Berkeley', `Herbert', and `E-176' were among the most susceptible. The consistent resistant reaction of certain cultivars indicates that they may be suitable as parents for introducing resistance into a breeding program. No significant correlation was observed between blighting resistance and fruit infection resistance.

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Self- and cross-fertility was evaluated in the highbush blueberry cultivars Bluegold, Duke, Legacy, Nelson, Sierra, Sunrise, and Toro, all released since 1987, by comparing them to standards of `Bluecrop' and `Rubel'. Percent fruit set increased with cross-pollination in all cultivars except `Bluecrop', which decreased by 13%. The average increase in the recently released cultivars was 43%. Fruit weight also increased in cross-pollinations for all cultivars except `Rubel', which showed a decrease of 2%. Average increase in fruit weight on cross-pollination in the recently released cultivars was 27%. Fruit set and fruit weight measurements suggest that `Duke', `Legacy', and `Nelson' could perform well in solid stands, but `Sierra' and `Toro' are more likely to need cross-pollination for best yields. Investigations were also made on a group of 10 cultivars, to evaluate whether ripening time of the pollen source cultivar had any effect on the ripening time of the fruiting parent. No single pollen source had consistent general effects on ripening, although specific combinations of females and males appeared to either hasten or delay ripening. The largest deviations were seen in delays of ripening, suggesting that poor pollination may have been the greatest factor contributing to the observed variation in ripening times.

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Abstract

Regardless of season, location, harvest date, or size, ‘Wolcott’ blueberry fruits sorted with transmitted light according to their anthocyanin (ACY) contents were reasonably well separated for quality as expressed by pH, titratable acid (AC), soluble solids (SS) and the SS/AC ratio. Quality of fruits of the same ACY class differed according to cultivar (‘Wolcott’, ‘Berkeley’, and ‘Jersey’). AC content of the fruit decreased slightly during the season regardless of ACY class or cultivar. This consistent reduction in AC as the season progressed was accompanied by increases in the SS/AC ratios and development of decay. Location of harvest (farm to farm) influences SS somewhat. A long harvest interval produced a small but consistent effect on all quality parameters.

Open Access

The resistance of 48 highbush blueberry cultivars and selections to the blight phase of mummy berry disease, incited by the fungus Monilinia vaccinii-corymbosi (Reade) Honey, was examined in relation to percent Vaccinium angustifolium Ait. ancestry, season of fruit maturity, and shoot growth during the primary infection phase. Correlations of percent blighting with percent V. angustifolium ancestry were significant across 3 years, but correlations with fruit maturity were significant in only 2 of 3 years. Correlations of percent blighting with early shoot growth were significant in both years measured, with r values of 0.54 in 1994, 0.83 in 1995, and 0.83 across years. A multiple regression found only shoot growth highly significant for susceptibility and rendered V. angustifolium ancestry and season of fruit maturity nonsignificant. Resistant cultivars exhibiting early shoot elongation suggest that resistance can be either biochemically or escape based.

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Abstract

Fruit of ‘Bonita’ and ‘Beckyblue’ rabbiteye blueberry (Vaccinium ashei Reade) cultivars were harvested weekly, then stored in two different types of consumer baskets and subjected to five time/temperature storage regimes. Fruit increased in total soluble solids (TSS) and pH and decreased in acidity (Ac) with advancing harvest dates. Total soluble solids and pH of ‘Bonita’ fruit were significantly lower and Ac higher than for fruit of ‘Beckyblue’. After 3 weeks of storage at 1°C plus 3 days at 16°, ‘Beckyblue’ had higher (8 times) decay than fruit of ‘Bonita’. There were no cultivar differences in fruit firmness or weight loss due to storage, but fruit weight was reduced significantly when packaged in molded pulp fiberboard baskets. Fruit of ‘Bonita’ can be used for both domestic and export markets, requiring long storage duration, but ‘Beckyblue’ fruit should be limited to domestic markets.

Open Access

Fourteen highbush blueberry cultivars are being evaluated in south central Missouri mineral soil. This soil is often not ideal for culture of highbush blueberry. The planting site was initially pH 6.3 with a 92% base saturation on the cation exchange capacity. Sulfur additions, and summer and fall cover cropping were done for 2 years prior to planting to lower soil pH (5.3) and increase organic matter content. Four replications of three plants were set in a randomized complete block in early Apr. 1998. Plant spacing is 1.2 × 3.0 m on bermed rows that are mulched with chipped hardwood. Acidified irrigation water is supplied through drip lines. Fertilizer is applied annually both as dry ammonium sulfate and soluble nitrogen through drip lines at 84 kg·ha-1 N. Cumulative yield per bush after the first five harvest seasons showed `Bluecrop', `Brigitta Blue', `Chandler', `Darrow', `Legacy', `Nelson', and `Reka' at 17 to 21 kg; `Duke', `Nui', `Ozarkblue', and `Sierra' at 14 to 15 kg; and `Collins', `Summit', and `Toro' at 9 to 10 kg. Berry weight averaged 2 g with a low of 1.4 g (`Reka') to a high of 3.3 g (`Chandler'). Plant height averaged 155 cm with a low of 117 cm (`Nui') to a high of 188 cm (`Legacy', `Nelson'). Cultivars in the two higher yield groups were recommended to Missouri growers for planting.

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Seven highbush blueberry cultivars were inoculated with one of three different isolates of ericoid mycorrhizal fungi (EMF) and grown in pots for 2 years with either inorganic or organic fertilizer. Root colonization of noninoculated plants was low (<15%) regardless of fertilizer source. Root colonization on inoculated plants was 15-30%. Colonization was typically higher when plants were grown with organic fertilizer. Inoculation generally increased plant growth but decreased root:shoot biomass ratios regardless of the type of fertilizer used. Inoculation also increased nutrient uptake and/or nutrient use efficiency in several cultivars, particularly when plants were fertilizer with organic fertilizer. Without inoculum, however, some cultivars fertilized with organic fertilizer had less growth and lower concentrations of N, K, S, and Cu than those fertilized with inorganic fertilizer. Cultivars that were genetically close in ancestry showed a high degree of variability in response to mycorrhizal fungi, while responses to fertilizer type were similar in closely related cultivars. Results suggest that nutrient availability may influence colonization and growth responses to EMF; however aspects of fungus–host specificity and inoculum availability also play a role in EMF colonization of roots in container production.

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Rabbiteye blueberry (Vaccinium ashei Reade) cultivars differ in timing of floral and vegetative budbreak and in final fruit size. For example, `Bonita' exhibits concomitant floral and vegetative budbreak and has relatively large fruit size, while floral budbreak precedes vegetative budbreak in `Climax' and fruit size is smaller. Mobilization of carbohydrate before and during fruit development in `Bonita' and `Climax' rabbiteye blueberries was examined to determine if differences in carbohydrate availability between these two cultivars were correlated with differences in fruit size. Root dry mass (DM) of both cultivars decreased from dormancy (31 days before anthesis) through fruit development. Sugar concentrations in roots and stems of both cultivars decreased significantly between dormancy and anthesis, then remained relatively steady throughout fruit development. Starch concentrations in roots and stems of `Bonita' decreased significantly between dormancy and anthesis. The extent of total starch depletion in `Climax' was similar; however, the decrease was more gradual, extending from dormancy to 28 days after anthesis (DAA); at which time, vegetative budbreak in `Climax' occurred. Thus, although total reserve carbohydrate pool sizes were similar between the two cultivars, remobilization patterns were different, resulting in increased starch mobilization in `Bonita' compared to `Climax' in the period leading up to anthesis. Concentration of 14C from reserve carbon sources was similar in flowers of both cultivars at anthesis. These values declined throughout fruit development as a result of dilution of the labeled carbon by unlabeled carbon from current photosynthesis. There was a sharper decline in 14C concentration of `Bonita' fruit compared to `Climax' fruit between anthesis and 51 DAA. This, coupled with differences in timing of vegetative budbreak between the two cultivars, suggests that `Bonita' fruit were accessing current (unlabeled) assimilate earlier (i.e., before 51 DAA) than `Climax' fruit. Smaller fruit size in `Climax' compared to `Bonita' may be a consequence of a decrease in reserve carbohydrate mobilization to `Climax' flower buds before anthesis relative to `Bonita', as well as a delay or reduction in the availability of current carbohydrates to developing `Climax' fruit between anthesis and 51 DAA.

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To determine if blueberry shoestring virus (BBSSV) is absent in the southern United States due to resistance of cultivars, we mechanically and rub-inoculated 1-year-old rooted microshoots of nine cultivars representing southern rabbiteye (Vaccinium ashei Reade), southern highbush (hybrids of V. corymbosum and V. darrowi Camp), and northern highbush (V. corymbosum L.). Leaves were sampled from plants, and enzyme-linked immunosorbent assay screened for the presence of virus over 15 months. Only a few individuals were infected after aphid inoculation, but many northern and southern cultivars became infected after mechanical inoculation. Northern highbush `Elliot' (50%) and `Blueray' (46.3%) had the highest infection rates, followed by rabbiteye `Climax' (36.3%) and the southern highbush `O'Neal' (12.5%). The lowest rates of infection were found in southern highbush `Georgiagem' (2.5%), `Misty' (2.5%), rabbiteye `Brightwell' (0.0%), and northern highbush `Bluecrop' (2.5%). Since many southern cultivars were infected by the disease, resistance likely has not excluded BBSSV from the southern United States.

Free access

Abstract

Drip irrigation applied to cultivars of rabbiteye blueberry (Vaccinium ashei Reade) maintained soil moisture at 25 to 35%, (volume basis), –0.07 bars soil-water potential while no irrigation resulted in 12.5% soil moisture, –2 to –3 bars. Irrigation reduced leaf diffusive resistance (rL) by 50% and increased transpiration (T) by 70% but had no significant effect on midday stem xylem pressure potentials (ψx ). Both yield and berry weight from irrigated plots were increased from 20 to 25% over those on nonirrigated plots. Seasonal changes in ψx , rL, and T of nonirrigated bushes suggested this species has some characteristic adaptations to drought conditions, one such adaptation being wax rodlets observed in and adjacent to stomatal pores. These may have contributed to a favorable water balance under stress by increasing leaf diffusive resistance.

Open Access