Scab Development Research Articles

Analysis of a Regional Characteristic for Japanese Pear Scab Development by Utilization of the Weather Data Obtained from AMEDAS (Automated Meteorological Data Acquisition System)

Analysis of a Regional Characteristic for Japanese Pear Scab Development by Utilization of the Weather Data Obtained from AMEDAS (Automated Meteorological Data Acquisition System)

Relationship between aerial concentration of Venturia inaequalis ascospores and development of apple scab

The relationship between the aerial concentration of pathogenic spores and amount of disease produced on susceptible plants is fundamental to developing models for predicting the spread of airborne diseases. This relationship was examined for apple scab, a disease important in many parts of the world. Potted McIntosh apple trees were exposed in the field to Venturia inaequalis ascospores naturally discharged during rain. Ascospore concentration in the air, ( C) (spores m −1), was monitored using spore samplers. Following exposure, trees were incubated under controlled conditions for infection and lesion development. In a separate experiment, individual leaves on potted McIntosh trees were quantitatively inoculated with V. inaequalis ascospore suspensions in the laboratory to determine the lesion-causing efficiency, ( E), of ascospores. E varied with leaf age and was about 0.2 lesions per spore for the most susceptible leaves (approximately 3–5 days after unfurling). The number of lesions per shoot, N S, was recorded for trees exposed in the field. A significant positive correlation ( r 2 = 0.54, P < 0.00001, d.f. = 293) was found between N S and exposure to ascospore concentration ( C × exposure time). A physical model was used to estimate deposition, D (spores m −2), of ascospores onto leaves for a given exposure to C. These calculated values of D were combined with experimentally determined values of E and the area of exposed leaves to estimate values of N S. Values of N S estimated using the model were well correlated ( r = 0.83, P < 0.01) with field observations.

Distribution and Development of Black Dot, Verticillium Wilt, and Powdery Scab on Russet Burbank Potatoes in Washington State

Plant samples were collected from 10 commercial fields of Russet Burbank potatoes in south-central Washington and assayed for Colletotrichum coccodes, Verticillium dahliae, and Spongospora subterranea 13 times between 21 May and 29 August 1990. Three fields were likewise surveyed seven times between 30 May and 20 August 1991. Colony-forming units of C. coccodes and V. dahliae were quantified in sap expressed from stem sections. Powdery scab galls were counted on roots (.)

Correlation of phytotoxin production with pathogenicity ofStreptomyces scabies isolates from scab infected potato tubers

A total of 23 isolates obtained from scab infected potato tubers representative of six sampling areas in Eastern and Central Canada and five ATCCStreptomyces strains were screened for pathogenicity on the basis of their ability to initiate scab development on aseptically cultured minitubers and plant generated tubers. The results were then correlated with any associated generation of the scab inducing phytotoxin, Thaxtomin A. In all cases a positive correlation was demonstrated between the pathogenicity of variousStreptomyces scabies isolates and their ability to produce the phytotoxin.

Relationship between Japanese Pear Scab Development and Nutrients Content in Leaves on Trees Given Different Amounts of Nitrogen Fertilizer.

The correlation between the development of Japanese pear scab (caused by Venturia nashicola) on leaves and the content of total nitrogen, total carbon, phosphorus, potassium, calcium, magnesium, iron and manganese in the leaves on trees given different amounts of nitrogen fertilizer was investigated. With an increase of nitrogen fertilizer, the content of total nitrogen and manganese in leaves increased while calcium content decreased. The content of total carbon, phosphorus, potassium, magnesium and iron did not show any obvious change. The ratio of diseased leaves, degree of disease development and degree of conidial formation increased with increasing amounts of given nitrogen fertilizer. Significant correlation (P=0.05) were recognized between total nitrogen content and the degree of disease development on 3rd and 7th position leaves from top leaf, the degree of conidial formation on 11th position leaf, calcium content and degree of disease development on 7th position leaf, and manganese content and degree of conidial formation on 7th position leaf. These results show that with an increase in nitrogen fertilizer there is an increase in total nitrogen and manganese content and a decrease in calcium content in leaves, and a higher susceptibility to Japanese pear scab was induced.

Forecasting of Primary Apple Scab Development with a Dew Balance

Forecasting of Primary Apple Scab Development with a Dew Balance

Change of Japanese pear scab development on scale lesion, numbers of produced conidia and ratio of germination

Change of Japanese pear scab development on scale lesion, numbers of produced conidia and ratio of germination

Control of apple diseases and pests with low spray volumes and reduced chemical rates

Fungicides applied in volumes of either 100, 200 or 800 l/ha controlled apple scab in large-scale field experiments from 1982 to 1985. Either Sonax C, a formulated mixture of etaconazole and captan applied at 1 kg/ha (one-third the recommended rate), or fenarimol at 112 ml/ha (one-quarter the recommended rate), controlled scab when applied in 100 or 200 l/ha respectively. Scab was controlled with either eight protectant or at least five eradicant applications of Sonax C at either 3 or 1 kg/ha in 200 1 of water per hectare. In all years, weather conditions favoured the development of scab. In unsprayed trees the incidence of scabbed fruit ranged from 60% in cv. Granny Smith to 26% in cv. Jonathan. In sprayed trees fruit infection rarely exceeded 1%. The control of powdery mildew was unsatisfactory with Sonax C applied at 1 kg in 100 l/ha. Better control was achieved by either increasing the spray volume or the rate of fungicide per hectare. Two-spotted and European mites were controlled with propargite at the recommended rate of 5·5 kg/ha at either 200 or 800 l/ha. Codling moth was controlled with 160 ml/ha of azinphos-methyl (one-quarter the recommended rate) applied in 800 l/ha.

Evidence for a relationship between certain soil arthropods and acid scab development

Springtails and mites have been found consistently in acid scab lesions and studies have shown that these arthropods carryStreptomyces spp. both on and in their bodies. Tests with several soil-applied, systemic insecticides have shown significant control of acid scab despite having little effect on the acid scab pathogen in culture. Diazinon, a long residual insecticide, gave acid scab control as good as the best fungicides thus far tested as seed or soil treatments. This insecticide also was found to be almost nontoxic to the acid scab pathogen. We suggest that soil arthropods appear to be a factor in acid scab development and present circumstantial evidence suggestive of their involvement in all potato scab development.

Development of Apple Scab on Fruit in the Orchard and During Cold Storage

Sensibilite des pommes a l'infection par Venturia inaequalis au cours du cycle de vegetation. Le taux de developpement des lesions sur les fruits entreposes et l'effet de l'infection sur la qualite sont determines

Effect of Time of Inoculation withCladosporium caryigenumon Pecan Scab Development and Nut Quality

Effect of Time of Inoculation with<i>Cladosporium caryigenum</i>on Pecan Scab Development and Nut Quality

Decreased severity of potato common scab after foliar sprays of 3,5 ‐dichlorophenoxyacetic acid, a possible antipathogenic agent

SUMMARYGlasshouse tests on the potato cultivars Majestic and Maris Bard measured the effects of single early foliar sprays of ring‐substituted phenoxyacetic acids (0.9 × 10–3 M) on the incidence of potato common scab, caused by soil‐borne Streptomyces scabies.The most effective compound was 3,5‐dichlorophenoxyacetic acid (3,5‐D), which decreased scab by about 90%; its action was preventative, early sprays being more effective than late However, it slightly decreased yield, and increased the number of tubers per plant and the proportion of deformed tubers. The trichloro‐ and tetrachloro‐ acids containing the 3,5‐dichloro‐ group also decreased scab, though to lesser extents; the most active of these was the 2,3,4,5‐tetrachloro‐ acid, which had the same side effects as 3,5‐D. The herbicide 2,4‐D almost halved scab incidence, but seriously decreased yield. Other acids tested had little or no effect on scab.In tests against S. scabies in culture, 3,5‐D was no more toxic than other disubstituted acids which were inactive, or weakly active, against the disease in vivo.3,5‐D may be an ‘antipathogenic agent’, preventing scab development by altering tuber metabolism.

Disease measurement in a study of apple scab epidemics

SUMMARYAn epidemic of apple scab in an unsprayed planting at East Mailing was monitored during the summer of 1979. Different rates and patterns of scab development on six apple cultivars were observed. Of several disease measures investigated the number of colonies/extension shoot best represented the epidemic.More comprehensive disease measurements on leaves, fruits and shoots were made toward the end of the summer. Cultivar differences were demonstrated for all disease measures investigated. The proportion of leaves with scab (incidence) and the number of colonies on leaves (intensity) were the measures with the lowest coefficients of variation. Consistent relationships between incidence and intensity were obtained.The implications of these findings for studies concerned with fungicide evaluation, cultivar susceptibility, disease—quality loss relationships and monitoring for disease management are discussed.

The Production of Experimental Dermatophyte Lesions in Guinea Pigs

Experimental dermatophytoses were induced in virgin and previously infected guinea pigs by the quantitated application of spores to plucked and shaved areas of skin. Lesions could be consistently induced without occlusion with 7 dermatophytes— Trichophyton mentagrophytes, T. rubrum, T. tonsurans, Microsporum canis, M. gypseum, M. persicolor and Epidermophyton floccosum . The progress of lesions was monitored visually and their infectivity determined using a hair brush sampling technique. Airborne spread of fungal elements from infected animals to other animals housed in the same area and to the atmosphere was also examined. With 2 dermatophytes, T. mentagrophytes and M. canis , it was found that the infectivity of lesions correlated well with the clinical progress of the disease after primary infection and on reinfection. This was not the case with the other fungi investigated where factors such as absence of hair invasion, hair invasion wholly or mainly endothrix in nature, or the development of a thick scab which trapped hairs and fungal elements, resulted in the development of lesions of low infectivity. Dissemination of spores into the air and onto neighboring noncontact animals occurred readily with M. canis , and to a lesser degree with T. mentagrophytes . Airborne spread of fungal elements from lesions due to the other dermatophytes was negligible. On reinfection, some spores germinated and hyphal growth occurred but lesions appeared earlier, healed more rapidly and were markedly less infective. This experimental model with T. mentagrophytes , would seem an ideal system for investigating the effects of various procedures, e.g., antimycotic therapy, vaccination, on the progress and infectivity of dermatophyte lesions.

Influence of Spray Adjuvants and Multiple Applications of Benomyl and Oil on Photosynthesis of Apple Leaves1

Abstract Spray adjuvants alone and combined with benomyl in single and multiple applications were tested for their influence on net photosynthesis (Pn) and development of apple scab caused by Venturia inaequalis (Cke.) Wint. on trees of apple (Malus domestica Borkh.) grown in the greenhouse. Triton CS-7 increased and ×-100 and 70 second oil deceeased Pn. Nu Film 17, Triton B-1956, Regulaid and ×-77 when combined with benomyl had no influence on Pn. Addition of Biofilm, Nu Film 17 or 70 second oil to benomyl did not improve apple scab control. Three sprays of benomyl plus oil decreased Pn of fully expanded leaves, and 5 sprays decreased Pn of both expanded and newly expanding leaves with the latter showing the greatest reduction.

Difference between shoots and branches in development of pear scab

Difference between shoots and branches in development of pear scab

Comparison of Some New Fungicides for the Control of Scab and Powdery Mildew of Apple

SUMMARYIn 1969, apple scab was controlled equally well by spraying at 14 or 28 day intervals with benomyl (0.025 per cent a.i.). Triarimol (0.004 per cent a.i.) at 14‐day intervals was even more effective and also surpassed benomyl in controlling apple mildew.In 1970, when the dry summer prevented apple scab development, triarimol apphed at 10‐day intervals again provided the best control of apple mildew. Sprays of thiophanate (NF 35) (0.05 per cent a.i.) and thiophanate‐methyl (NF 44) (0.05 per cent a.i.) applied at 10‐day intervals were no better than the standard captan/dinocap programme, but triarimol and benomyl at 21‐day intervals were less effective.

Shifts in disease resistance induced by growth regulators

Experiments on the effect of various compounds with plant growth regulating activity led to the hypothesis that conditions inhibitory to indoleacetic acid (IAA) action or leading to a decrease in the IAA level in cucumber seedlings would be unfavourable for the development of cucumber scab, caused byCladosporium cucumerinum. Susceptibility decreased as the result of treatment with growth retardants, which cause an increase in IAA-oxidase activity in the plants, whereas application of indoleacetic acid or compounds expected to decrease the rate of oxidative breakdown of IAA in the seedlings resulted in an increase of susceptibility. Growing the plants under various periods of illumination also influenced both the susceptibility of the plants and the IAA-oxidase activity in the hypocotyl tissue. To obtain further information about the relation between the increase in resistance and the increase in the rate of IAA oxidation, the effect of one compound, viz. L-threo-β-phenylserine (abbr. phenylserine) was studied in more detail. The rate of oxidative breakdown of IAA was increased in extracts of hypocotyls and cotyledons of plants treated with phenylserine as compared with extracts of tissue of untreated plants. Extracts of phenylserine-treated plants were found to contain a higher cofactor and/or a lower inhibitor content than those of control plants. The substances involved were not identified, but this result may indicate a shift in the concentrations of various phenols in the tissue. The question must remain open whether a shift in the concentration of phenols some-how effected by phenylserine treatment determines both degree of susceptibility and rate of IAA oxidation independently, or whether the rate of IAA breakdown and the resulting change in IAA content in the plants is directly related to the degree of susceptibility. Proeven over het effect van verschillende verbindingen met groeiregulerende werking leidden tot de volgende hypothese: onder omstandigheden waarin de werking van indolylazijnzuur (IAZ) wordt belemmerd of het gehalte aan IAZ in de planten afneemt, wordt de ontwikkeling van vruchtvuur, veroorzaakt doorCladosporium cucumerinum, bij komkommerkiemplanten geremd. De vatbaarheid verminderde door de behandeling met verbindingen die een toename van de activiteit van IAZ-oxydase in de planten veroorzaken, terwijl behandeling met IAZ of met stoffen, waarvan verwacht mag worden dat ze de afbraak van IAZ remmen, de vatbaarheid juist verhoogde. Ook bij kweken van de planten bij verschillende belichtingsperioden namen de vatbaarheid en de activiteit van de IAZ-oxydase gelijktijdig toe, respectievelijk af. Het verband tussen de verandering in de activiteit van IAZ-oxydase en in resistentie werd nader onderzocht aan de hand van een bestudering van het effect van L-threo-β-fenylserine (afgekort: fenylserine). Door extracten van hypocotylen en cotylen van met fenylserine behandelde planten werd IAZ sneller afgebroken dan door extracten van onbehandelde planten. Er werder aanwijzingen verkregen, dat de oorzaak hiervan een hoger gehalte aan cofactoren en/of remstoffen is, die de omzetting beinvloeden. Er is niet vastgesteld om welke verbindingen het gaat; het is echter waarschijnlijk dat hierbij fenolen zijn betrokken. Of een verandering in de concentratie van de verschillende fenolen zowel verant-woordelijk is voor de verandering in de mate van resistentie en voor de veranderde mate van afbraak van IAZ, dan wel of het laatstgenoemde verschijnsel en de daaruitvoortvloeiende verandering in het IAZ gehalte rechtstreeks verband houdt met de resistentiegraad kon niet worden vastgesteld.

The influence of manganese on the development of potato scab

The development of common scab on potato crops growing in slightly acid to neutral soils has been shown to be greatly reduced by application of manganese sulphate to the soil at planting time. A general improvement in health and appearance of tubers was noted and increased yields of marketable tubers were obtained. The possibility that environmental factors known to influence the development of scab are only important in so far as they affect the solubility of soil manganese is discussed.

Influence of time of planting of potatoes in indiana muck soil on yield and scab development

Time-of-planting experiments were conducted with potatoes on the Northern Indiana Muck Soils Experimental Farm, near Walkerton, Indiana, during the period from 1939 to 1942. Both total yields and yields of marketable or essentially scab-free potatoes, were determined for crops from plantings made at 5 two-week intervals from about the 5th of May to the 5th of July.