Browsing by Author "Lillo, C"

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    Effects of temperature, free moisture duration and inoculum concentration on infection of sweet cherry by Pseudomonas syringae pv. syringae
    (2002) Latorre, BA; Lillo, C; Rioja, ME
    The effects of temperature, free moisture duration and inoculum concentration on infection caused by Pseudomonas syringae pv. syringae (Pss), on sweet cherry (Prunus avium) were investigated. Epiphytic populations of Pss are an important source of inoculum for bacterial canker and it has been demonstrated that a cyclic pattern exists during the year, from undetectable during the warm and dry periods to large populations following cool and wet periods. The effects of temperature and inoculum concentration on the infection caused by Pss on immature fruits and 1-yr-old twigs were significant (P<0.001). Fruit and twig infection increased linearly in proportion to the logarithm of Pss when bacterial concentrations were higher than 10(3) cfu ml(-1) and temperatures were between 5 and 20 °C. Regardless of the inoculum concentration and the free moisture duration, fruit and twig infection was either absent or low at 5 °C but it increased linearly as temperature increased from 5 to 20 °C. Growth rate in vitro was very slow (0.03-0.04 cfu h(-1)) at 5 °C and fast (0.21-0.23 cfu h(-1)) at 20 °C. Therefore, it is possible that multiplication of the epiphytic populations may be significantly reduced in the field with air temperatures below 5 °C. A significant (P<0.001) effect of free moisture was obtained only when a low inoculum concentration (10(3) cfu ml(-1)) was used, and a significant linear response between free moisture and disease incidence was obtained only at 10degreesC. An apparent threshold population of Pss higher than 10(3) cfu ml(-1) was needed to infect immature fruits and 1-yr-old twigs of sweet cherry.
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    The effect of temperature and wetness duration on infection and a warning system for European canker (Nectria galligena) of apple in Chile
    (2002) Latorre, BA; Rioja, ME; Lillo, C; Muñoz, M
    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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    The effect of temperature on infection and a warning system for pear blossom blast caused by Pseudomonas syringae pv. syringae
    (ELSEVIER SCI LTD, 2002) Latorre, BA; Rioja, ME; Lillo, C
    Blossom blast caused by Pseudomonas syringae pv. syringae van Hall, is a major disease of pears (Pyrus spp.) in Chile. Freezing temperatures may predispose pears to infection, however, our results demonstrated that blossom blast infection might occur in the absence of frosts, at temperature higher than 5degreesC, provided that the appropriate inoculum concentration, moisture levels and the susceptible bloom stages were available. Regardless of the flower bud stage development, blossom blast was lowest at 5degreesC and highest at 20degreesC. The first symptoms appeared after 2-3 days at 20degreesC, and were delayed 2 days at 5 C. A significant and positive linear regression best explained the relationship between disease incidence and temperature. A warning system, based on temperature and free moisture conditions, was developed and found to be useful for prediction of blossom blast infection in the field. Antibiotic treatments applied after each warning significantly (p<0.05) reduced blossom blast on Packham's Triumph pears. (C) 2002 Elsevier Science Ltd. All rights reserved.