The Importance of Wood Scab caused by <i>Venturia inaequalis</i> (Cke.) Wint. as a Source of Infection for Apple Leaves in the Spring<sup>2</sup>)

Hill, Steven A.

doi:10.1111/j.1439-0434.1975.tb03486.x

Cited by 16 publications

(14 citation statements)

References 7 publications

(4 reference statements)

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“…Although, several older studies demonstrated that conidia on scab lesions on woods or shoots overwintered in apple orchards (Cook and Schwarze, 1917;Marsh and Walker, 1932;McKay, 1938;Cook, 1974;Hill, 1975), scab lesions on branches or shoots in the sampled orchards were not found in this study. At several locations in Germany, it was demonstrated that scab conidia overwintered on the surface of shoots of scab susceptible cultivars (Kennel, 1981;Moosherr andKennel, 1986, 1995;Moosherr, 1990).…”

Section: Discussioncontrasting

confidence: 63%

“…Therefore, ascospore maturation and release as well as the occurrence of Mills infection periods during ascospore release are key elements to be considered in scab control strategies (Szkolnik, as wood, twig, shoot and bud and might cause early infections in spring (McAlpine, 1902;Cook and Schwarze, 1917;Salmon and Ware, 1931;Marsh and Walker, 1932;Dillion Weston and Petherbridge, 1933;Gloyer, 1937;McKay, 1938;Dillion Weston et al, 1952;Jeffrey, 1953;Swinburne, 1965;Cook, 1974;Hill, 1975;Jeger et al, 1982). However, these studies greatly varied in their opinion about the risk of early infection by overwintered conidia compared to the risk from ascospores.…”

Section: Introductionmentioning

confidence: 96%

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The widespread occurrence of overwintered conidial inoculum of Venturia inaequalis on shoots and buds in organic and integrated apple orchards across the Netherlands

Holb

Heijne²,

Jeger

2005

Eur J Plant Pathol

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A 2-year study was conducted to determine the widespread occurrence of overwintered conidial inoculum of Venturia inaequalis and its impact on the apple scab control in 18 apple orchards (organic and integrated) with various levels of scab in the Netherlands. Autumn assessments of scab lesions showed that the integrated orchards had a significantly lower scab incidence (<20%) compared to that of the organic orchards (>60%). At the bud-break phenological stage, the mean numbers of nonviable and viable conidia on 1 cm pieces of shoots ranged from 1 to about 90 and from 6 to more than 1000 in the integrated and the organic orchards, respectively, for both years. However, viable conidia on shoots were found only in 2 integrated and 6 organic orchards out of the 18 and the viability of conidia was below 2%. The mean numbers of viable and nonviable conidia per 100 buds ranged from 24 to more than 1000 and from 230 to almost 5000 in the integrated and the organic orchards, respectively, for both years. In both years, some 60-85% of the conidia was found on the outer bud scales. The percentage viability associated with the outer bud tissues was below 2% for all the orchards. However, the percentage of viable conidia within the inner bud tissues ranged from 0% to 6% in the integrated and from 2% to 11% in the organic orchards for both years. Differences between the organic and the integrated orchards were clearly demonstrated for overwintered conidia associated with both shoot and bud samples. The relationship between autumn scab incidence and numbers of overwintered conidia associated with shoots or buds was exponential. If the autumn scab incidence was above 40%, then the number of overwintered conidia markedly increased. We conclude that specific treatments for overwintering conidia of Venturia inaequalis may not be necessary in integrated orchards with a low scab incidence in the previous autumn. However, the risk of early scab epidemics initiated by overwintered conidia potentially is high in organic orchards. Preventative measures in early spring and also in the previous year must be established in these orchards.

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Section: Discussioncontrasting

confidence: 63%

Section: Introductionmentioning

confidence: 96%

The widespread occurrence of overwintered conidial inoculum of Venturia inaequalis on shoots and buds in organic and integrated apple orchards across the Netherlands

Holb

Heijne²,

Jeger

2005

Eur J Plant Pathol

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“…The role of wood scab in epidemics needs further attention (Swinburne, 1965;Hill, 1975), especially the relative weights that must be given to disease on different plant parts (Zadoks, 1972). Increase of scab on Laxton's Superb was rapid initially compared to subsequent increases.…”

Section: Discussionmentioning

confidence: 99%

“…This would have added to the inoculum load from ascospores. The role of wood scab in epidemics needs further attention (Swinburne, 1965;Hill, 1975), especially the relative weights that must be given to disease on different plant parts (Zadoks, 1972). Also, Laxton's Superb developed later than other cultivars and at the time of the Mills periods in May (Table 2) had more foliage at a vulnerable stage.…”

Section: Discussionmentioning

confidence: 99%

Disease measurement in a study of apple scab epidemics

Jeger¹

1981

Annals of Applied Biology

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An epidemic of apple scab in an unsprayed planting at East Malling 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.

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“…Venturia inaequalis can also overwinter asexually, potentially as stromata on twigs (Cook, ; Hill, ), or more probably as viable inoculum (most probably conidia) between bud scales (Becker et al ., ). As with conidia from lesions in the main epidemic phase, it is probable that conidia from overwintered sources will infect within an area close to the source of overwintered scab.…”

Section: Introductionmentioning

confidence: 99%

The relative importance of conidia and ascospores as primary inoculum of Venturia inaequalis in a southeast England orchard

et al. 2017

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Apple scab, caused by Venturia inaequalis, can lead to large losses of marketable fruit if left uncontrolled. The disease appears in orchards during spring as lesions on leaves. These primary lesions are caused by spores released at bud burst from overwintering sources; these spores can be sexually produced ascospores from the leaf litter or asexual conidia from mycelium in wood scab or within buds. The relative importance of conidia and ascospores as primary inoculum were investigated in an orchard in southeast England, UK. Potted trees not previously exposed to apple scab were placed next to (c. 1 m) orchard trees to trap air-dispersed ascospores. Number and position of scab lesions were assessed on the leaves of shoots from both the potted trees (infection by airborne ascospores) and neighbouring orchard trees (infection by both ascospores and splash-dispersed, overwintered conidia). The distribution and population similarity of scab lesions were compared in the two tree types by molecular analysis and through modelling of scab incidence and count data. Molecular analysis was inconclusive. Statistical modelling of results suggested that conidia may have contributed approximately 20-50% of the primary inoculum in early spring within this orchard: incidence was estimated to be reduced by 20% on potted trees, and lesion number by 50%. These results indicate that, although conidia are still a minority contributor to primary inoculum, their contribution in this orchard is sufficient to require current management to be reviewed. This might also be true of other orchards with a similar climate.

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The Importance of Wood Scab caused by Venturia inaequalis (Cke.) Wint. as a Source of Infection for Apple Leaves in the Spring²)

Cited by 16 publications

References 7 publications

The widespread occurrence of overwintered conidial inoculum of Venturia inaequalis on shoots and buds in organic and integrated apple orchards across the Netherlands

The widespread occurrence of overwintered conidial inoculum of Venturia inaequalis on shoots and buds in organic and integrated apple orchards across the Netherlands

Disease measurement in a study of apple scab epidemics

The relative importance of conidia and ascospores as primary inoculum of Venturia inaequalis in a southeast England orchard

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The Importance of Wood Scab caused by Venturia inaequalis (Cke.) Wint. as a Source of Infection for Apple Leaves in the Spring2)

Cited by 16 publications

References 7 publications

The widespread occurrence of overwintered conidial inoculum of Venturia inaequalis on shoots and buds in organic and integrated apple orchards across the Netherlands

The widespread occurrence of overwintered conidial inoculum of Venturia inaequalis on shoots and buds in organic and integrated apple orchards across the Netherlands

Disease measurement in a study of apple scab epidemics

The relative importance of conidia and ascospores as primary inoculum of Venturia inaequalis in a southeast England orchard

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The Importance of Wood Scab caused by Venturia inaequalis (Cke.) Wint. as a Source of Infection for Apple Leaves in the Spring²)