The effect of temperature and wetness duration on infection and a warning system for European canker (<i>Nectria galligena</i>) of apple in Chile
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2002
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Abstract
European canker (Nectria galligena Bres.) is a major disease of apple in Chile, mainly producing cankers on twigs and branches. Disease incidence over 50% has been reported on 'Richard Red' apples in Southern Chile. In vitro, conidial germination of N. galligena was low at 6degreesC and 32degreesC, and optimum germination temperature was estimated between 20degreesC and 25degreesC. Ascospore germination was low at 5degreesC and rapidly increased as temperature increased from 5degreesC to 20degreesC. Germination rate, calculated as germination frequency over time at 20degreesC, was 2.3 times faster for ascospores than conidia, and germination of ascospores increased 2.6 times faster than conidia as temperature increased from 5degreesC to 20degreesC. Infection caused by conidia of N. galligena through leaf scars was significantly dependent on temperature and free moisture duration. However, regardless of the wetness duration no infection was obtained at 5degreesC. This is in agreement with the lack of conidial germination obtained below 6degreesC by in vitro studies. Disease incidence increased linearly with temperatures between 5 and 20degreesC. Based on our results, a 2-h moisture period was enough to promote a significant infection at 20degreesC but longer moisture periods were needed at lower temperatures. An infection warning system, based on the analysis of weather parameters, was developed and implemented in the predictive software PatFrut((C)). Over two seasons, the warning system was an effective tool for determination of the need of fungicide treatments against European canker. Significant differences in disease incidence and severity were obtained reducing disease incidence from over 24% in 1999 to 4.6% when treatments were schedule according to the model program. Differences in severity, but not disease incidence were found between the model program and the standard program. This forecast model assumed that conidia, produced during leaf fall were not a limiting factor. It also assumed that susceptible leaf scars were continuously available between March and July. The protective fungicide treatments applied during leaf fall significantly reduced infection in the next season suggesting that leaf scars are important infection courts for N. galligena on apples. (C) 2002 Elsevier Science Ltd. All rights reserved.
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disease forecast, fungicides, Malus, predictive model