Sweet cherries (Prunus avium) can be one of the most profitable tree fruit cultivated in temperate climates. While cherry trees grow naturally to relatively tall heights, new size-controlling cherry rootstocks similar to those used in high-density apple orchards are now a reality. The Gisela series from Germany, the Gran Manier series from Belgium, the Weiroot series, the P-HL series, Tabel Edabriz, and others of international origin are at various stages of scientific and field testing in North America, with some now moving into commercial fruit production. These stocks confer several highly advantageous traits besides vigor control, including precocious fruiting and high productivity. While these obvious traits are exciting, serious problems have also been documented, on occassion, with such phenomena as small fruit size and tree decline. As many of these rootstocks are interspecific Prunus hybrids, might there be significant limitations for fruit quality and orchard longevity? What is known about their susceptibilities to pathogens and pests? What is known about their tolerance to various soil types and/or climatological stresses? Further, with the U.S. and worldwide orchard area planted to fresh-market sweet cherries already expanding to record levels throughout the 1990s and a time-honored agricultural trend toward overproduction until grower profits are minimized (see recent international apple markets), what might be the future impact of such precocious, productive rootstocks on sweet cherry profitability and sustainable production? This overview will address these topics, providing some answers and some areas for future scientific investigation and discussion.
Attempts to discuss the various aspects of plant dormancy can be bewildering due to the excessive number of nonphysiological, independent terms that have arisen over the years. In the context of field observations and orchard management, this terminology has often been adequate. However, in the complex realm of scientific description of the processes that constitute dormancy, the terminology has not been able to keep pace with physiological investigation. In 1985, a set of alternative terms, endodormancy, ectodormancy, and ecodormancy, were suggested to improve the situation (14). During the past 2 years, R. Darnell, J. Early, G. Martin, and I have reviewed the dormancy literature to evaluate the strengths and weaknesses of new and previous terms. At various times, N. Arroyave, R. Biasi, R. Femandez-Escobar, G. Stutte, and others from around the world have contributed greatly to discussion and critical analysis of the requirements for a physiological nomenclature. In 1986, ectodormancy was replaced by paradormancy (16) due to the former’s spoken and written similarities to ecodormancy. This paper summarizes the communicative burden presented by the current terminology, the evolution of the new terms, the universal classification system in which the terms are used, and the implications for future dormancy research. These topics are presented in greater detail elsewhere (15).
Sweet cherries (Prunus avium L.) can be one of the most profitable tree fruits cultivated in temperate climates. While cherry trees grow naturally to relatively tall heights (≈35 ft [≥10 m]), new size-controlling cherry rootstocks similar to those used in high-density apple (Malus domestica Borkh.) orchards are now a reality. The Gisela (GI.) and Weiroot (W.) series from Germany, the Gran Manier (GM.) series from Belgium, the P-HL series from Czech Republic, `Tabel Edabriz' from France, and others of international origin are at various stages of scientific and field testing in North America, with some now being used for commercial fruit production. These stocks confer several advantageous traits besides vigor control, including precocious fruiting and high productivity. While these beneficial traits are exciting, serious problems also have been documented on occasion, such as small fruit size and tree decline. As many of these rootstocks are interspecific Prunus L. hybrids, might there be significant limitations for fruit quality and orchard longevity? What is known about their tolerance to various soil types and/or climatological stresses? What is known about their susceptibilities to pathogens and pests? Further, with the U.S. and worldwide orchard area planted to fresh-market sweet cherries already expanding to record levels throughout the 1990s and a time-honored agricultural tendency toward overproduction until grower profits are minimized (e.g., recent international apple markets), what might be the future impact of such precocious, productive rootstocks on sweet cherry profitability and sustainable production? This overview addresses these topics, providing some answers and some areas for future scientific investigation and industry discussion.
High tunnel production systems typically use horticultural crops that are annually or biennially herbaceous, high in value, short in stature, and quick to produce. At best, tree fruits may fit only one of these criteria–high value. Sweet cherry (Prunus avium) may command high enough values in premium market niches to make high tunnel production strategies worth attempting. Furthermore, sweet cherry production can be a risky endeavor, even in optimal climates, due to the potentially devastating effects of preharvest rain that cause fruit cracking. Consequently, environmental modification by tunnels in regions like the Great Lakes provides a significant risk reduction. Additional potential benefits, such as protection from frosts, diseases, insects, wind scarring, etc., add further production value. Multi-bay high tunnels were constructed in 2005 at two Michigan State University experiment stations, over established and newly planted sweet cherry trees on dwarfing rootstocks, to study and optimize the effects of production environment modification on vegetative and reproductive growth, marketing season extension, and protection of cherries from diseases, insect pests, and/or physiological disorders. Results with tunnels thus far include premium fruit quality and high crop value; increased leaf size and terminal shoot growth; decreased radial trunk growth; decreased chemical pesticide inputs; decreased incidence of cherry leaf spot (Blumeriella jaapii) and bacterial canker (Pseudomonas syringae); increased incidence of powdery mildew (Podosphaera clandestina); inconclusive effects on brown rot (Monolinia fructicola); no or reduced infestation by plum curculio (Conotrachelus nenuphar) or cherry fruit fly (Rhagoletis cingulata); dramatically reduced japanese beetle (Popillia japonica) damage; and increased black cherry aphid (Myzus cerasi) and two-spotted spider mite (Tetranychus urticae) populations.
Pollen deposition on the stigmatic surface of blueberry pistils was studied with regard to maximum pollen load and stigmatic fluid production (stigma receptivity). Three hybrid southern highbush cultivars (Vaccinium corymbosum L. with V. darrowi Camp, V. ashei Reade, and/or V. angustfolium Aiton), two northern highbush cultivars (V. corymbosum), and one hybrid half-high cultivar (V. corymbosum with V. angustifolium) were selfand cross-pollinated with counted pollen tetrads until saturation of the stigmatic surface occurred. Stigmatic saturation generally required 200 to 300 tetrads and was characterized by the cessation of stigmatic fluid production and the inability to absorb further tetrads. The loss of stigmatic receptivity was irreversible. Cross-pollination resulted in cessation of stigmatic fluid production at lower levels of tetrad deposition than did self-pollination, suggesting a potential pollen-stigma recognition phenomenon. Northern highbush, half-high, and southern highbush cultivars required 7% to 10%, 12% to 17%, and 14% to 21%, respectively, more self-pollen to develop the stigmatic saturation condition. The potential relation of the pollenstigma phenomenon to self-incompatibility mechanisms is discussed.
Pollen from six southern highbush blueberry cultivars derived from Vaccinium corymbosum L. and one or more other species (V. darrowi Camp, V. ashei Reade, and V. angustifolium Aiton) was incubated on nutrient agar to determine tetrad viability, pollen tube growth rates, and incidence of multiple pollen tube germinations. `Avonblue' pollen had a significantly lower tetrad germination percentage than `Georgiagem', `Flordablue', `Sharpblue', `Gulfcoast', or `O'Neal', all of which had >90% viable tetrads. The in vitro growth rate of `O'Neal' pollen tubes was significantly higher than the growth rates of `Sharpblue' and `Georgiagem pollen tubes. Of those tetrads that were viable, more than two pollen tubes germinated from 83% and 91% of the `Gulfcoast' and `Sharpblue' tetrads, respectively, while only 11% of the `Flordablue' tetrads produced more than two pollen tubes. The total number of pollen tubes germinated per 100 tetrads ranged from 157 (`Flordablue') to 324 (`Sharpblue'), resulting in actual pollen grain viabilities ranging from 39% to 81%. Genetic differences in pollen vigor, as indicated by pollen viability, pollen tube growth rates, and multiple pollen tube germinations, may influence blueberry growers' success in optimizing the beneficial effects of cross-pollination on fruit development.
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.
To initiate photosynthetic studies of sweet cherry (Prunus avium L.) canopy architectures and cropping management under high light and temperature conditions (Yakima Valley, Wash.), we developed a whole-canopy research cuvette system with a variable airflow plenum that allowed different patterns of air delivery (in concentric circles around the trunk) into the cuvette. Air and leaf temperatures (Tair and Tleaf, respectively) were determined at four horizontal planes and four directional quadrants inside cuvette-enclosed canopies trained to a multiple leader/open-bush or a multiple leader/trellised palmette architecture. Air flow rate, air delivery pattern, and canopy architecture each influenced the whole-canopy temperature profile and net CO2 exchange rate (NCER) estimates based on CO2 differentials (inlet-outlet). In general, Tair and Tleaf were warmer (≈0 to 4 °C) in the palmette canopy and were negatively correlated with flow rate. The response of Tair and Tleaf to flow rate varied with canopy position and air delivery pattern. At a flow of 40 kL·min-1 (≈2 cuvette volume exchanges/min), mean Tair and Tleaf values were 2 to 3 °C warmer than ambient air temperature, and CO2 differentials were 15-20 μL·L-1. Tair and Tleaf were warmer than those in unenclosed canopies and increased with height in the canopy. Carbon differentials declined with increasing flow rate, and were greater in the palmette canopy and with a less dispersed (centralized) delivery. Dispersing inlet air delivery produced more consistent values of Tair and Tleaf in different canopy architectures. Such systematic factors must be taken into account when designing studies to compare the effects of tree architecture on whole-canopy photosynthesis.
Most sweet cherry (Prunus avium L.) cultivars grown commercially in the United States are susceptible to powdery mildew, caused by the fungus Podosphaera clandestina (Wall.:Fr.) Lev. Recently, hybrid populations segregating for resistance to powdery mildew were developed by crossing a mildew-resistant sweet cherry selection, PMR-1, with the susceptible cultivars Bing, Rainier, and Van. Although segregation within these populations indicated a single gene was responsible for the powdery mildew resistance conferred by PMR-1, the gene action could not be determined. Therefore, a reciprocal cross between `Bing' and `Van' was made to determine the allelic state of the susceptible parents used previously. All progeny (n = 286) from this cross were susceptible to powdery mildew. This information, combined with results from previous segregation data, indicate the powdery mildew resistance gene is inherited in a dominant manner and is present in PMR-1 in the heterozygous allelic state. We have named this gene Pmr1. Furthermore, in combination with known pedigree information, we have been able to predict the susceptibility of more than 60 additional commercial and recently released sweet cherry cultivars.