Hazelnuts, (Corylus avellana L.), are wind-pollinated, monoecious, mostly dichogamous, and self-incompatible. About 90% of the cultivars studied are protandrous. Anthesis of the pistillate flower is temperature-dependent and occurs December through February, peaking in January. Stigmatic surfaces may remain receptive for up to 3 months. Four to 5 months separate pollination and fertilization of the ovule; the latter usually occurring between mid-May and the end of June in Oregon. A 10% pollinizer density has been the standard, with a recommended distance of 66 ft (20 m) or less between the main cultivar and the nearest pollinizer. Two or three different pollinizer cultivars, with different times of pollen shed, are recommended. The Oregon hazelnut industry is presently combating the fungal disease, eastern filbert blight, caused by Anisogramma anomala (Peck). Current management recommendations suggest reducing risk of infection are to reduce the most susceptible pollinizer cultivars to a density 5%, then gradually replace those left with immune or more resistant genotypes.
Gladiolus flowers comprise an important part of the total cut flower industry in the United States, with a wholesale value of $17.1 million in 1979 (3). Of the 130 million spikes sold that year, 77 million were grown in Florida where the major production time is from October through May. A successful cut flower cultivar in Florida must be consistent in growth during continuous weekly plantings from August 15 through February, must producet all (≥ 110 cm) straight spikes with at least 14 floral buds per rachis, and must open from the “tight bud” stage following 2-3 days of cold storage (5°C). The cultivar also should be highly tolerant of major fungal diseases, especially Fusarium corm and root rots incited by Fusarium oxysporum Schlecht. f. sp. gladioli (Massey) Snyd. & Hans. (4).
Apple scab, a fungal disease caused by Venturia inaequalis, is considered the most important disease of apple worldwide. The disease can be devastating, causing reduction in yield or making the apples unfit for the market. Currently, the production of marketable fruit from scab susceptible cultivars depends on the repeated applications of fungicides. Scab-resistant apple cultivars, which are genetically immune to apple scab, can offer a biological alternative to fungicide use. `Liberty,' was bred for immunity to apple scab; however, it is not immune to other apple diseases and pests. Research has been conducted during a 3-year project (1996–1998) to determine whether reduced fungicide programs adversely affect overall tree vigor, productivity, and fruit quality. Data collected include tree vigor (TCSA and time of leaf abscission), tree productivity (YE), and fruit quality (fruit firmness and disorders during storage). Results indicate no significant differences between the two treatments (reduced fungicide and no fungicide application) in most of the parameters measured. Based on fruit that were harvested and graded to commercial standards, the estimated gross monetary value of the crop does not show difference between treatments. These results could translate into an economic advantage for growers when one factors in the savings in fungicide purchases. In addition, there are also health and environmental advantages to reduced fungicide usage.
There are many naturally occurring substances that have the potential to be adapted to modern pest control chemistry. Azadirachtin, an insect growth regulator, is one such naturally occurring compound that has been widely accepted in insect pest management. Quartenary benzophenanthridine alkaloids (QBAs) are known to be effective in the control of crop damaging fungal diseases. QBAs can be isolated from plants in the Papaveraceae. Extracts of Macleaya cordata, a species rich in QBAs, were formulated at 150 mg·L–1 QBA for spray application to greenhouse roses infected with Sphaerotheca pannosa var. rosae (powdery mildew). The QBA formulation was applied at 10-day intervals. Copper sulfate pentahydrate (Phyton27), piperalin (Pipron), and fenarimol (Rubigan) were also applied to mildew infected plants within the same greenhouse at their respective label rates for comparison. One day after treatment, the mildew infection was reduced 50% by QBA, whereas fenarimol, copper sulfate pentahydrate, and piperalin reduced the infection 50%, 75%, and 80%, respectively. Nine days after application, the mildew infection of QBA treated plants was less than 5% of the leaflet surface area. QBAs have the potential to be developed as a biorational fungicide for greenhouse use with both fungicidal and fungistatic activity.
The United States is the world's largest producer of blueberries and strawberries. Successful marketing for both of them requires fruit of the highest quality and appearance. However, these fruits have a relatively short postharvest life, mostly due to the incidence of molds such as Colletrotrichum acutatum, Alternaria alternata, and Botrytis cinerea. At present, several natural occurring plant volatiles have been shown to be effective against fungal growth, but, even so, those compounds could not be maintained at constant concentration during the whole postharvest period due to their volatility. In this work, two naturally occurring aldehydes (acetaldehyde and hexanal) were tested and compared against the growth of the above mentioned fungi at 23 °C. After that, the most effective antifungal compound for each fungus was encapsulated in ß-cyclodextrins (ß-CD) and tested during storage period. Both aldehydes were effective in reducing and avoiding fungal proliferation depending on concentration. Fungal proliferation depended on daily, and not initial, volatile concentrations. Volatiles encapsulated in ß-CD showed higher antifungal activity compared to that obtained using the pure volatile during storage. Tested volatiles showed both fungicidal and fungistatic capacities after storage of fungal cultures in air. Results suggested ß-CD-acetaldehyde and ß-CD-hexanal complexes can be used as a new technology to release a naturally occurring antifungal compound during storage against several fungal diseases.
A long-term experiment in the same site was planted to evaluate potential yield, nematode, and disease problems with tomatoes (Lycopersicon esculentum Mill.) in a strip-till system. Treatments consisted of conventional tillage (CT) and strip tillage (ST), rye (Secale cereale L.), wheat (Triticum aestivum L.), and perennial ryegrass (Lolium perenne L.) cover crops and a 2-year rye–tomato rotation. Results of the first 5 years indicate a decrease in tomato yield over time for both tillage treatments and cover crops. Tomato yields were lower following wheat and perennial ryegrass than rye. Strip-tillage reduced yield compared to conventional tillage in only 1 year out of 6. Yield increased overall for treatments in 1992, with highest yield in the rye–tomato rotation. Bacterial speck/spot symptoms on foliage, although minor, were significantly greater in ST than in CT plots during the last 3 years. No major consistent trends in incidence and severity of bacterial and fungal diseases and of disorders of fruit were evident during the 5-year period, and neither fruit yield nor quality were significantly affected by these factors. Root-knot nematodes (Meloidogyne hapla Chitwood) were numerically less numerous in the rye–tomato rotation than in other treatments; both root-knot and root lesion nematodes [Pratylenchus penetrans (Cobb)] tended to be less numerous under CT than under ST. Tomatoes grown under reduced tillage appear more sensitive to plant parasitic nematodes and preceding cover crops than in conventional tillage.
Virus and fungal disease pressures limit fall production of summer squash (Cucurbita pepo L.) in Kentucky. Twenty-five summer squash cultivars (nine zucchini, eight yellow straightneck, and eight yellow crookneck entries) were evaluated for marketable yield, appearance, and disease resistance in a late summer planting. Genetically engineered virus-resistant materials and new conventionally bred resistant or tolerant cultivars were compared with popular susceptible hybrids. Virus incidence was determined visually before and after final harvest and was also determined by enzyme-linked immunosorbent assay (ELISA). Watermelon mosaic virus (WMV) was most frequently detected and appeared to have caused most of the observed symptoms. Conventionally bred cultivars containing the precocious yellow gene and two transgenic lines were in the highest yielding group of yellow straightneck squash despite high virus incidence in precocious yellow cultivars. Among yellow crooknecks, transgenic cultivars were clearly superior for disease resistance and yields. Conventionally bred cultivars with virus tolerance were among the highest yielding zucchini types. Most transgenics were superior to their nontransformed equivalent cultivars for virus resistance and yield. Cultivars and breeding lines varied considerably in color, shape, and overall appearance. ELISA results revealed that some (but not all) transgenic cultivars tested positive for the coat protein corresponding to the virus resistance present in that cultivar. Also, mild virus-like symptoms were observed in transgenic squash plants after the conclusion of harvest.
Transpiration and water uptake play an important role in the growth of horticultural crops, such as tomatoes. Water uptake ensures the transport of nutrients. However, the transpiration rate is affected by the humidity level in the greenhouse. High levels of humidity restrict transpiration and lead to fungal diseases resulting in yield losses. Under northern latitudes, using more airtight structures combined with high levels of artificial lighting increase the humidity level inside the greenhouses. To decrease humidity, growers have to dehumidify by ventilating and heating at the same time, leading to increased energy consumption. However, to our knowledge, the literature does not report on the energy consumption needed to dehumidify. To evaluate this energy consumption, we used a greenhouse simulation model of heat and mass exchanges integrated into a general greenhouse control and management software system (GX). Evapotranspiration, condensation on the cladding, and infiltration and ventilation rates were taken into account for the water balance. Based on 1 year of climatic data, three sets of simulation were realized: 1) no dehumidification; 2) standard dehumidification by ventilation and heating; 3) dehumidification with heat exchangers. Results indicate that for an acceptable level of humidity within a greenhouse tomato crop (vapor pressure deficit >5 kPa), the energy consumptions with standard dehumidification and with heat exchangers are 25% and 15% higher, respectively, than without dehumidification. These results are being used to establish recommendations for the management of humidity under northern latitudes.
Citrus black spot is an important fungal disease of citrus resulting in fruit drop and rind blemish in tropical and subtropical production areas. The disease is incited by the fungus Phyllosticta citricarpa (McAlpine) van der Aa (synonym: Guignardia citricarpa Kiely), with control currently relying on the application of fungicides. Because the presence and expression of resistance is poorly understood, we sought to develop a method for inoculating fruit in the field that gives reproducible symptoms of citrus black spot consistent with natural field infection. We subsequently validated this method by screening 49 citrus accessions and characterized their qualitative expression of citrus black spot symptoms. Challenge inoculations were undertaken with a known isolate of P. citricarpa, and control fruit were inoculated with water or the endophyte P. paracapitalensis Guarnaccia & Crous. Our results showed that all mandarin, sweet orange, lemon and papeda types were susceptible; pummelo, lime, and sour orange types expressed immunity; while various hybrids were susceptible, resistant and immune. Hybrid progeny from crosses using pummelo [Citrus maxima (Burm.) Merr.] as a parent showed preliminary evidence of segregation for citrus black spot immunity. The implications of these results to achieve genetic improvement for citrus black spot resistance in citrus breeding programs are discussed.
A chitinase gene (pcht28), isolated from Lycopersicon chilense, was transferred into `Joliette' strawberry using a stipule regeneration method and Agrobacterium-mediated gene transfer technique. Stipules showed a high rate of shoot regeneration (>90%) through direct or indirect organogenesis. Stipules were cocultured with a transformation plasmid in which pcht28 was under the control of the CAMV 35S promoter. A high tendency in production of chimaeric shoots was observed. Shoots which did not show any sign of bleaching after several subcultures in kanamycin containing medium were considered as stable transformants. These shoots were successfully rooted in the presence of 50 μg·mL-1 kanamycin. Transgenic nature of the plants was confirmed by PCR as well as Southern blot analysis. Constitutive expression of the chitinase gene was demonstrated by Northern analysis. In growth chamber studies, the transgenic strawberry plants which expressed pcht28 had significantly higher resistance to Verticillium dahliae as compared to nontransgenic controls. These results demonstrate that pcht28 plays a role in defense against this fungal disease in strawberry.