Abiotic Disorders Research Articles

Etiology and Management of a Mandarin Rind Disorder in California.

Recent reports of a preharvest rind disorder of Satsuma mandarin fruit resulted in severe crop losses in some growing areas of California (Butte, Fresno, Tulare, and Kern Counties). Symptoms were more frequently observed on fruit on the outer perimeter of the tree and on the exposed side of the fruit. Fungal isolations from affected fruit were inconsistent among orchard sites and growing seasons. Isolations resulted in species of Alternaria, Fusarium, Macrophomina, Ulocladium, and Cladosporium. In laboratory studies, mandarin fruit that were soaked in water for 6 h at 15 to 35°C, air dried, and incubated at 20°C for 3 days developed lesions similar to those observed in the field. When fruit were treated with an agricultural summer spray oil or the antitranspirant di-1-p-menthene prior to water soaking, the incidence and severity of the disorder were significantly reduced. Similar results were obtained in 2 years of field trials at two sites using one to three preharvest applications with the agricultural antitranspirant or summer oil starting after fruit color break. In most trials, a single application of these treatments at 1 or 2 weeks after color break was highly effective. Fungicides were inconsistent in their efficacy, whereas trees that were physically protected from rain did not develop the disorder. These data suggest that this mandarin rind disorder is a physiological, abiotic disorder rather than a pathological problem caused by fungi and can be economically managed with water-repellant treatments.

BIOTIC AND ABIOTIC FACTORS IN SOIL-BORNE DISEASES IN STRAWBERRY NURSERIES

Strawberry runners are a high-value cash crop in Spain that requires vigorous transplants free of pathogens. Ten different methyl bromide alternatives with an experimental randomized block design were applied, including methyl bromide and non-treated parcels in all the experiments like positive and negative controls since 1998 to 2007 in several strawberry nursery fields located in Castilla-Leon (Spain). Two field experiments where conducted each year with fumigant applications prior to planting. The results showed that more than 50% of the diseased symptomatic plants were not infected with soil borne pathogens. Furthermore, there are no correlations between the symptomatic plants without pathogens recorded and the treatment applied. Interaction between the symptoms produced by the main soil-borne pathogens in strawberry nurseries and other abiotic disorders was discussed, especially because the effect of chemical treatments against soil-borne pathogens can be overlapped.

Guidelines to Identification and Management of Plant Disease Problems: Part I. Eliminating Insect Damage and Abiotic Disorders

PP248/MG441- PP251/MG444, a 4-part series by Aaron Palmateer, Ken Pernezny, Monica Elliott, and Nikol Havranek, are new additions to the Master Gardener Handbook. They provide beginning Master Gardener volunteers with methods for taking a systematic approach to diagnosis of plant disease problems. Published by the UF Department of Plant Pathology, February 2008. PP248/MG441: Guidelines to Identification and Management of Plant Disease Problems: Part I. Eliminating Insect Damage and Abiotic Disorders (ufl.edu) Ask IFAS: Guidelines to Identification and Management of Plant Disease Problems series (ufl.edu)

Diseases, pests, and abiotic disorders of greenhouse-grown water spinach (Ipomoea aquatica) in Ontario and California

Water spinach, a specialty vegetable and a member of the sweet potato family, is cultivated for Asian markets in California (United States) and Ontario (Canada). Foliar diseases of this vegetable observed in commercial greenhouses of Ontario in 1993 and 1994, as well as in greenhouses of California in 1998, were attributed respectively to Phyllosticta ipomoeae, Cercospora ipomoeae, and Pseudomonas syringae pv. syringae in the present study. In Ontario, C. ipomoeae infected less than 1% of plants, with less than 25% of the foliage affected, while Phyllosticta ipomoeae occurred on 100% of plants in some greenhouses, with leaf spotting affecting up to 25% of the foliage. In California, Pseudomonas syringae pv. syringae occurred on less than 25% of plants with up to 25% of the foliage affected. In Ontario, no virus was detected in eight suspect foliage samples while damage from vectors of plant viruses such as the green peach aphid (Myzus persicae) was minor and from Western flower thrips (Frankliniella occidentalis) was moderate. Edema affected water spinach at four sites in Ontario in 1994, with both the incidence and severity exceeding 75% at one site. For fungal and bacterial pathogens, Koch's postulates were fulfilled by inoculation and reisolation. Morphological characteristics of isolates in vitro and in vivo were used to identify the fungal pathogens, and LOPAT tests and fatty acid analyses were applied to identify the bacterial pathogen. Symptoms and etiology are discussed. This is the first report of these diseases, pests, and abiotic disorders on water spinach in Ontario and California.

INFLUENCE OF DIFFERENT SUBSTRATES AND NUTRIENT SOLUTIONS ON THE YIELDS AND THE INCIDENCE OF ABIOTIC DISORDERS OF BROCCOLI

INFLUENCE OF DIFFERENT SUBSTRATES AND NUTRIENT SOLUTIONS ON THE YIELDS AND THE INCIDENCE OF ABIOTIC DISORDERS OF BROCCOLI

Landscape Tree Cultivar Preferences in Iowa, U.S.

A survey questionnaire was mailed to all 142 active members of the Iowa Nursery and Landscape Association to characterize landscape tree cultivar preferences among green-industry professionals and their clients. Respondents identified Acer rubrum 'Franksred' (Red Sunset® red maple), Acer saccharum 'Green Mountain' (sugar maple), Acer platanoides 'Pond' (Emerald LustreÔ Norway maple), Acer ´ freemanii 'Jeffersred' (Autumn Blaze® Freeman maple), Fraxinus americana 'Junginger' (Autumn Purple® white ash), Fraxinus pennsylvanica 'Patmore' (green ash), Gleditsia triacanthos var. inermis 'Skycole' (Skyline® honeylocust), Tilia americana 'Redmond' (American linden), and Tilia cordata 'PNI 6025' (Greenspire® littleleaf linden) as the best-selling cultivars within nine species of trees. Betula nigra 'Cully' (Heritage® river birch) and Malus 'Prairifire' (crabapple) were identified as the best-selling cultivars in their respective genera. Considering all landscape trees sold in Iowa, our respondents identified Acer ´ freemanii 'Jeffersred' (Autumn Blaze® Freeman maple) as the overall best-selling selection. Overuse of these popular selections, however, could be problematic should any prove susceptible to serious, health-threatening insects, diseases, or abiotic disorders.

378 Calcium–Boron Regimes Effect Incidence of Postharvest Disorders on Poinsettia Bracts

Incidences of poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bract disorders like the pathogen Botrytis cinerea and the abiotic disorder bract necrosis are related to nutrient stress. `Supjibi' poinsettias were grown hydroponically with four Ca-B combinations of 0 or 4 mm Ca added with either 5 or 120 μmol B added. Forty-one days after initial anthesis, plants were harvested and their bracts subdivided into true-bracts and transitional-bracts for determination of incidence of botrytis lesions and bract necrosis. Mineral nutrients in bract margins were determined for leaves, transitional-bracts and true-bracts. Leaf margins had the highest concentrations of Ca and B. Margins of transitional-bracts had substantially lower concentrations and margins of true-bracts the least. The low Ca (0 mm) or low B (5 μmol) treatments greatly reduced the concentrations of these elements, respectively, in all three tissue types. The low Ca-low B treatment increased the incidence of bract necrosis on true-bracts from 1.9% on controls (4 mm Ca, 120 μmol B) to 27%. Low Ca treatment increased bract necrosis on transitional-bracts from 1.6% on controls to 24.3%. Bract necrosis incidence was the same on true-bracts and transitional-bracts, whereas the incidence of botrytis was higher on transitional-bracts than on true-bracts. Botrytis incidence was increased for true-bracts and transitional-bracts by plant exposure to low Ca solutions compared to plants in 4 mm Ca. Low Ca reduced growth in roots, but not shoots. Ca and B stress to roots increased the incidence of bract necrosis on true-bracts, while only Ca stress increased incidence of botrytis.

377 Differential Response of Two Poinsettia Cultivars to Calcium Stress for Postharvest Disorders

Poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bracts are susceptible to postharvest disorders like the pathogen Botrytis cinerea and the abiotic disorder bract necrosis that degrade plant appearance. `Freedom Red' and `Supjibi' poinsettias were grown hydroponically with Ca concentrations of 0.5 or 4 mm. Forty days after initial anthesis, plants were harvested and their bracts subdivided into true-bracts and transitional-bracts for determination of incidence of botrytis lesions and bract necrosis. Mineral nutrients in bract margins were determined only for true-bracts. Margin Ca concentrations were relatively high in true bracts only for `Supjibi' plants exposed to 4 mm Ca solutions. Botrytis incidence was increased for transitional-bracts but not true-bracts for both cultivars by plant exposure to low (0.5 mm) Ca solutions compared to control (4 mm Ca) plants. The smaller the poinsettia roots relative to shoots, the higher the incidence of botrytis for `Freedom Red' transitional-bracts and `Supjibi' true-bracts. Botrytis incidence was higher on transitional-bracts (13%) than on true-bracts (3.5%) for both cultivars exposed to low Ca, whereas the incidence of bract necrosis on `Supjibi' was the same on true-bracts and transitional-bracts in either Ca solution. Bract necrosis was not evident on `Freedom Red' plants in either the 0.5 or 4-mmmm Ca solutions, however for `Supjibi' exposure to low Ca solutions increased incidence of bract necrosis from 5.5% for controls to 19.3%. The effect of Ca stress applied to poinsettia roots was genotype dependant for bract necrosis but not for botrytis.

ForestHealth, an expert advisory system for assessing foliar and crown health of selected northern hardwoods

Assessment of tree health requires accurate estimates of crown condition and identification of specific biotic and abiotic agents that may affect crowns, stems, or roots. ForestHealth, an expert advisory system written in C language for the Macintosh™ platform, provides a diagnostic module and two training modules. The diagnostic module provides guidance in identifying foliar symptoms and the common insects, diseases, and abiotic disorders found on leaves of: sugar maple (Acersaccharum Marsh.), red maple (Acerrubrum L.), black cherry (Prunusserotina Ehrh.), northern red oak (Quercusrubra L.), and white oak (Quercusalba L.). Graphical user interfaces are central to both training modules. The Foliar Severity routine trains users to categorize injury (percent leaf area) on single leaves using a modified Horsfall–Barratt scale. The Crown Dieback routine displays different types and degrees of crown injury that users must identify and classify. Each crown is unique, generated in "real time" using tree–branch parameters selected by the user. Since the crowns are created on a three-dimensional basis, multiple views are possible. Written output from training sessions or periodic checks provide quantitative information for quality assurance and quality control. ForestHealth provides diagnostic assistance, training, quality assurance and quality control data, and standardization for research or survey projects involving forest health.

Diagnosis and incidence of diseases associated with a decline of sweet cherry trees in California orchards

Abstract In recent years, a heavy loss of sweet cherry (Prunus avium L.) trees has occurred in California. During 1985 and 1986, several orchards were examined and the findings revealed that several biotic agents and abiotic disorders, all capable of causing tree decline or nonproductiveness, were represented in affected orchards. Confirmation of disease identification for a representative number of symptomatic trees was accomplished by a variety of test procedures including DNA hybridisation assay for the X-disease MLO.