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Southern highbush (“low chill tetraploid”) blueberries are an earlier-ripening, self pollen-compatible alternative to rabbiteye blueberries. `Sharpblue', the first southern highbush cultivar planted on a commercial scale, has been shown to require cross-pollination for optimal fruit size and earliness of ripening. `Gulfcoast', a recently released cultivar for Gulf states growers of about latitude 30 to 32 N, differs in heritage from `Sharpblue', incorporating about 50% more self-compatible northern highbush germplasm. `Gulfcoast' fruit development after honey bee-mediated self- or cross-pollination with `Sharpblue' was similar in terms of set (85.5 vs. 82.2%), weight (1.26 vs. 1.18g), and seed number (32.8 vs. 33.6), respectively. Cross-pollination did not result in significantly earlier ripening. Thus, `Gulfcoast' appears to be more self-fertile than `Sharpblue'. Other closely-related cultivars are being examined to determine the genetic influence on potential for self-fruitfulness.
`Gulfcoast' southern highbush blueberry (Vaccinium corymbosum × V. darrowi) plants were placed in 3 × 6 × 2.5 m net cages with one colony of honey bees per cage and one of three pollinizer treatments: “self (other `Gulfcoast' plants), “cross/highbush” (other southern highbush cultivars), or “cross/rabbiteye” (various rabbiteye blueberry cultivars). In addition to unlimited pollination, bee foraging was controlled on individual flowers by placing small bags over corollas after 0, 1, 5, or 10 visits. Fruit set, fruit weight, fruit development period, and seed number data were taken, as well as data to relate floral morphology to duration of bee foraging. All measures of fruiting increased significantly with increased bee visitation; the threshold for significant gains in production occurred between 1 and 5 visits. Ten visits generally provided a good approximation of unlimited pollination. Set, weight, and earliness of ripening was as good, or better, for fruit derived from rabbiteye pollen compared to fruit from self- or cross/highbush-pollination.
To study self- and cross-pollination effects on fruit development in southern highbush (mainly Vaccinium corymbosum L.) blueberries, `Sharpblue' plants were caged with honey bees (Apis mellifera L.) and other `Sharpblue' or `Gulfcoast' plants at anthesis. Ratios of pollinizer: fruiting flowers ranged from 2.1 to 4.5. Cross-pollination increased fruit size by ≈14% and seed count by 27% but did not influence fruit set. Overall, seed count decreased by 58% during the 30 days of harvest, but this did not directly affect fruit size. Seed count appeared to influence earliness of ripening as much as it influenced fruit size. Cross-pollination increased the harvest percentage of early-ripening fruits by ≈140% and of premium market fruits (those ≥ 0.75 g) by 13% and decreased the percentage of small fruits by 66%. Consequently, a 43% increase in premium early market crop value (nearly $5000/ha) resulted from optimizing `Sharpblue' cross-pollination.
Abstract
A laboratory system was developed to study olive (Olea europaea L.) organ abscission (21). An improvement of the use of ethylene-releasing compounds in this system is described to provide a model for field abscission responses and characterization of ethylene release. Olive fruit began the separation process as early as 7 to 13 hr after treatment with CGA-15281 (CGA), but not until 19 to 25 hr after treatment with ethephon (ET). CGA is characterized by an immediate, substantial breakdown to ethylene, whereas ET reaches its maximum ethylene release at 12 to 18 hr after application. Ethylene release was much greater from CGA than from equimolar concentrations of ET throughout the abscission initiation period. The relation of ethylene release characteristics to control of olive fruit and leaf abscission is discussed, with the suggestion that fruit respond more rapidly to, and at shorter durations of applied ethylene than do leaves.
Most sweet cherry (Prunus avium L.) cultivars grown commercially in the Pacific Northwestern states of the United States are susceptible to powdery mildew, caused by the fungus Podosphaera clandestina (Wall.:Fr.) Lev. The disease is prevalent in the irrigated arid region east of the Cascade Mountains in Washington State. Little is known about genetic resistance to powdery mildew in sweet cherry, although a selection (PMR-1) was identified at Washington State Univ.'s Irrigated Agriculture Research and Extension Center that exhibits apparent foliar immunity to the disease. The objective of this research was to determine the inheritance of powdery mildew resistance from PMR-1. Reciprocal crosses were made between PMR-1 and three high-quality, widely-grown susceptible cultivars (`Bing', `Rainier', and `Van'). Resultant progenies were screened for reaction to powdery mildew colonization using a laboratory leaf disk assay. Assay results were verified by natural spread of powdery mildew among the progeny in a greenhouse and later by placing them among infected trees in a cherry orchard. Segregation within the progenies for powdery mildew reaction fit a 1 resistant: 1 susceptible segregation ratio (P ≤ 0.05), indicating that resistance to powdery mildew derived from PMR-1 was conferred by a single gene.
A personal computer-based method was compared with standard visual assessment for quantifying colonization of sweet cherry (Prunus avium L.) leaves by powdery mildew (PM) caused by Podosphaera clandestina (Wallr.:Fr.) Lev. Leaf disks from 14 cultivars were rated for PM severity (percentage of leaf area colonized) by three methods: 1) visual assessment; 2) digital image analysis; and 3) digital image analysis after painting PM colonies on the leaf disk. The third technique, in which PM colonies on each leaf disk were observed using a dissecting microscope and subsequently covered with white enamel paint, provided a standard for comparison of the first two methods. A digital image file for each leaf disk was created using a digital flatbed scanner. Image analysis was performed with a commercially available software package, which did not adequately detect slight differences in color between PM and sweet cherry leaf tissue. Consequently, two replicated experiments revealed a low correlation between PM image analysis and painted PM image analysis (r2 = 0.66 and 0.46, P ≤ 0.0001), whereas visual assessment was highly correlated with painted PM image analysis (r2 = 0.88 and 0.95, P ≤ 0.0001). Rank orders of the 14 cultivars differed significantly (P ≤ 0.05) when PM image analysis and painted PM image analysis were compared; however, rankings by visual assessment were not significantly different (P > 0.05) from those by painted PM image analysis. Thus, standard visual assessment is an accurate method for estimating disease severity in a leaf disk resistance assay for sweet cherry PM.
Most sweet cherry (Prunus avium L.) cultivars grown commercially in the Pacific Northwest U.S. are susceptible to powdery mildew caused by the fungus Podosphaera clandestina (Wall.:Fr.) Lev. The disease is prevalent in the irrigated arid region east of the Cascade Mountains in Washington State. Little is known about genetic resistance to powdery mildew in sweet cherry, although a selection (`PMR-1') was identified at the Washington State Unive. Irrigated Agriculture Research and Extension Center that exhibits apparent foliar immunity to the disease. The objective of this research was to characterize the inheritance of powdery mildew resistance from `PMR-1'. Reciprocal crosses between `PMR-1' and three high-quality, widely-grown susceptible cultivars (`Bing', `Rainier', and ëVaní) were made to generate segregating progenies for determining the mode of inheritance of `PMR-1' resistance. Progenies were screened for susceptibility to powdery mildew colonization using a laboratory leaf disk assay. Assay results were verified by natural spread of powdery mildew among the progeny seedlings in a greenhouse and later by placement among infected trees in a cherry orchard. Progenies from these crosses were not significantly different (P > 0.05) when tested for a 1:1 resistant to susceptible segregation ratio, indicating that `PMR-1' resistance is conferred by a single gene, which we propose to designate as PMR-1.
A detached leaf disk assay for screening sweet cherry (Prunus avium L.) genotypes for susceptibility to powdery mildew (PM) [Podosphaera clandestina (Wallr.:Fr.) Lev.] was developed by evaluating the effects of photoperiod (24 hours light, 0 hours light, 14 hours light/10 hours dark), substrate nutrient content (sterile distilled water, 1% sucrose), leaf age (old, young, emergent), and leaf explant size (intact leaf, 30 mm, 20 mm) on PM growth on leaves from the susceptible cultivar Bing. The only parameter described that had a significant (P ≤ 0.001) effect on PM growth was leaf age. Old leaves, designated as the third fully expanded leaf from the basal end of current-year's shoot growth, were never infected with PM under controlled inoculations. In the absence of significant differences between treatments, those parameters with the highest treatment means were selected for subsequent evaluation. To test the leaf disk assay, 14 sweet cherry cultivars were screened in two experiments, and rated according to level of PM susceptibility. Rank sum comparison of results from cultivars used for leaf disk screening agreed with earlier field rankings of the same cultivars. The developed leaf disk assay greatly reduced the space required to screen sweet cherry cultivars, and was a repeatable and objective predictor of field resistance that may be useful for screening germplasm or breeding populations.
Five-year old `Sharpblue' southern highbush blueberry plants (Vaccinium corymbosum L.) were self- and cross-pollinated (`O'Neal') to study peroxidase (POD) activity, isozyme patterns, and histological localization during fruit development. Cross-pollination resulted in larger and earlier-ripening fruit. Activities of soluble and bound POD were very high during fruit growth period I, with peaks at 10 and 20 days after self- and cross-pollination. Activity was much higher for cross-pollinated fruit. During fruit growth period II, POD activities were low in both pollination treatments. During ripening, soluble POD increased, then declined in both treatments. Bound POD activities increased during the color transition from blue to dark blue, with the increase greater in self-pollinated fruit. Banding patterns of soluble and bound POD isozymes and their histological localization varied by pollination treatment as well as fruit developmental stage. During fruit ripening, soluble POD activity appeared to be associated with color transition from light blue to blue, while bound POD activity appeared to be associated with color transition from blue to dark blue.
Ovule abortion occurred between 5 and 10 days after pollination (DAP) in self- and cross-pollinated `Sharpblue' blueberry (Vaccinium corymbosum L.) fruit. More ovule abortion occurred with self-pollination (35%) than with cross-pollination (22% for `Sharpblue' × `O'Neal' and 29% for `Sharpblue' × `Gulfcoast'), and there were more poorly developed ovules with self-pollination (88.1%) than with cross-pollination (× `O'Neal', 33.6%; × `Gulfcoast' 50.8%). The increase in ovule area correlated exponentially with fruit growth during early developmental stages, regardless of pollination treatment. However, cross-pollination resulted in significantly greater ovule area and fruit mass during early fruit development as well as at ripening. Ovule area was maximum at 25 to 30 DAP for both pollination treatments, followed by exponential fruit growth (stage III). Cross-pollination resulted in greater fruit growth and a shorter stage III. At 10 DAP, ovules from cross-pollination were larger than those from self-pollination, suggesting that cross-pollination initiated ovule growth immediately after fertilization. This research suggests that southern highbush blueberry fruit growth and development is intimately associated with ovule growth and development, which is affected by pollen sources.