A synthetic autotetraploid derived by colchicine treatment of a Vaccinium elliottii Chapm. plant (2n = 2x = 24) was used to study the effect of chromosome doubling on the ability of this noncultivated species to cross with the cultivated tetraploid highbush blueberry (V. corymbosum L.). Mean pollen germination was 28%1 for the autotetraploid plant, compared to 53% for the diploid V. elliottii plant. However, the number of seedlings obtained per flower pollinated on the tetraploid highbush cultivar O'Neal rose from 0.01 when diploid V. elliottii was the pollen source to 3.86 when pollen from the autotetraploid V. elliottii plant was used. Reciprocal crosses between diploid V. elliottii and its autotetraploid and selfs of the autotetraploid produced no seedlings. Meiotic irregularities, such as multivalent during metaphase, laggards, and unequal chromosome disjunction, were observed in the autotetraploid, but most chromosomes were associated as bivalents.
Blueberry is clonally propagated by hardwood and softwood cuttings, and by micropropagation. Zimmerman and Broome (7) reported 22.8 µm 1H-indole-3-acetic acid (IAA) plus 73.8 µmN-(3-methyl-2-butenyl)-1H-purin-6-amine (2ip) to be optimal for axillary shoot proliferation. Lyrene (4) found that 28.5 µm IAA added to medium containing 73.8 µm 2ip had no effect on shoot multiplication. Although lowbush blueberries produced increasingly more shoots as 2ip concentrations increased from 0 to 147.6 µm (2), three highbush clones produced fewer shoots at the 147.6 µm than at lower concentrations (1).
Pollination of about 7000 flowers of tetraploid highbush blueberry clones with pollen from a wild diploid species, V. elliottii (Chapm.) Small, gave 25 phenotypically obvious hybrids. Examination of 18 of these hybrids showed that they included triploids, tetraploids, pentaploids, and aneuploids. Some hybrids appeared to be mosaics, as evidenced by chromosome-number variability in premeiotic flower buds. Most hybrids were highly vigorous. The triploids were completely female sterile and the pentaploids ranged from partially to completely female sterile when open-pollinated. Three of the tetraploids examined were highly fertile and extremely vigorous. The occurrence of 3x-4x mosaicism suggests that the 3x hybrids may have arisen from chromosome loss in 4x plants rather than from 3x zygotes. Morphological similarities between certain of the 5x hybrids and the west Florida race of the native allohexaploid species V. ashei Reade suggest V. corymbosum L.–V. elliottii allohexaploidy as one possible mode of origin for V. ashei.
Date of 50% anthesis, date of 50% fruit ripening, length of fruit development period, fruit size, flavor, scar and color were determined for random samples of V. darrowi Camp, V. elliottii (Chapm.) Small, V. fuscatum Ait., and V. myrsinites Lam. growing in their native habitats in Alachua County, Florida. Mean berry weight ranged from 25.1 eg for V. fuscatum to 17.8 eg for V. myrsinites. V. elliottii flowered and ripened early, with only 60 days from flowering to ripening for 5 plants. V. myrsinites and V. darrowi flowered late, about 1 to 2 weeks after commercial V. ashei Reade, but ripened with V. ashei. Fruit ranged from shiny black to moderately glaucous for V. elliottii and V. darrowi but was black for V. fuscatum and V. myrsinites. Variance analysis suggested that selecting the best clone within a species is almost as important as selecting the best species in breeding most traits.
Nineteen native blueberry (Vaccinium ashei Reade) clones selected from several areas in northern Florida and southeastern Georgia were self- and cross-pollinated in a greenhouse. Fruit set for the 19 clones averaged 15% after self-pollination and 58% after cross-pollination. Viable seeds per berry averaged four for self-pollination and 11 for cross-pollination. Average berry weight was 0.7 g for self-pollination and 1.1 g for cross-pollination, and average interval from flowering to ripening was 106 days for selfing and 92 days for crossing. Following self-pollination, pollen germinated and pollen tubes grew down the style as rapidly as after cross-pollination.
A vigorous, compact wild rabbiteye blueberry (Vaccinium ashei Reade) plant (FL78-66) found in northeast Florida had short internodes, small leaves, and low apical dominance. S1 plants after one growing season average 31 cm tall compared to 62 cm for S1 plants from the V. ashei cultivar ‘Premier’. FL78-66 was highly fertile when crossed as male or female with V. ashei cultivars. Most F1 plants were full-statured, but some resembled FL78-66. F2 plants obtained by intercrossing short-statured F1 plants ranged from full statured to much more compact than FL78-66.
Fruit set, fruit size, and seed production after hand pollination in a greenhouse were compared for southern highbush blueberry managed in two ways: a) 69 clones were allowed to go dormant and lose their leaves in the field before being dug and subjected to 1000 hours at 5 °C and b) 26 clones were kept growing in a greenhouse through fall and winter without leaf loss and without chilling, to induce flowering on plants that had mature leaves. On each plant in both management systems, some flowers were self-pollinated, some were cross-pollinated, and others had the styles removed before anthesis to prevent pollination. For >1000 flowers per pollination treatment on the deciduous plants, fruit set averaged 1% for no pollination, 46% for self-pollination, and 76% for cross-pollination. The corresponding values for the evergreen plants were 23%, 59%, and 81%. Parthenocarpic berries averaged 0.37 g/berry for deciduous plants and 1.01 g for evergreen plants. Both crossed and selfed berry weights averaged slightly higher for the evergreen plants than for the deciduous plants, but seed number per berry was much lower for the evergreen plants (12 seeds in crossed berries and four seeds in selfed berries) compared to deciduous plants (37 and 8). Southern highbush blueberry plants that flower without going dormant appear to have much higher parthenocarpic capabilities than those that flower after a dormant period.
Eleven cultivars of Vaccinium ashei Reade in a 10-year-old planting were compared for number of flowers per inflorescence and for percentage of the flowers that set fruit on bagged and open-pollinated branches. Mean flower number per cluster ranged from 7.6 for ‘Bluegem’ to 5.3 for Florida-M. Mean percentage of fruit set on open-pollinated branches ranged from 75% for ‘Southland’ to 36% for ‘Tifblue’. On branches bagged to exclude bees, the range was from 21% for ‘Beckyblue’ to 3% for Tifblue.
Pollen germination differed significantly between and within 3 interspecific hybrid populations and their parents. Pollen germination of populations of ‘Sharpblue’ (Vaccinium X sp.) × V. myrsinites Lamark (38%) and ‘Sharpblue’ × V. darrowi Camp (33%) was lower than mid-parent means of 45% and 37%, respectively. ‘Avonblue’ × V. myrsinites averaged higher in pollen germination than the mid-parent, 42% vs. 32%. Pollen germination of ‘Sharpblue’ × V. myrsinites hybrids varied most in pollen germination, ‘Avonblue’ × V. myrsinites hybrids least, and ‘Sharpblue’ × V. darrowi hybrids intermediate.
V. myrsinites Lam. is most susceptible to canker among the blueberry species native to Florida and survives by resprouting from underground rhizomes. V. darrowi Camp suffers less canker damage than V. myrsinites, some mature colonies showing little or no damage but others being nearly destroyed by the disease. Most mature V. darrowi colonies in the State have some stems cracked and swollen by canker. Old native plants of V. ashei Reade and V. fuscatum Ait. show light to moderate canker damage in many parts of the State but both species are more resistant than the previous two. V. elliottii Chapm. shows no canker over much of its range in Florida, but localized populations have moderate to high infection. Only one cankered plant of V. arborewn Marsh, has been found, and no canker has been found on V. stamineum L.