Browsing by Author "Rioja, ME"

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    Occurrence of resistant strains of Botrytis cinerea to anilinopyrimidine fungicides in table grapes in Chile
    (ELSEVIER SCI LTD, 2002) Latorre, BA; Spadaro, I; Rioja, ME
    Effort to control gray mold caused by Botrytis cinerea failed in a table grapevine (Vitis vinifera) vineyard near Santiago, Chile where cyprodinil (Vangard 50 WP), a new fungicide of the anilinopyrimidine group, had been applied alone up to four times per year during two growing seasons. A relatively high frequency (38.5%) of resistant isolates of R cinerea (EC50 for mycelial growth inhibition varied from. 2.9 to 4.84 mug ml(-1)) may explain the partial loss of field control efficacy obtained. Resistance was correlated. with a complete loss of in vivo sensitivity to cyprodinil. Resistant. isolates of B. cinerea showed cross resistance to the anilinopyrimidines fungicides mepanipyrim and pyrimethanil. Cyprodinil partially impaired conidia germination and differentially affected conidial germination of resistant and sensitive isolates. Significant differences (p < 0.05) in growth rate, sclerotia production and osmotic sensitivity were found among isolates of B. cinerea, but no correlation could be drawn between these biological differences and resistance or sensitivity. This indicates a disruptive selection characteristic of monogenic resistance. Thus, strategies were implemented to avoid the further development and spread of resistance in B. cinerea to the anilinopyrimidine fungicides. To our knowledge this constitutes the first mention of resistance in B. cinema populations to anilinopyrimidine fungicides in South America. (C) 2002 Elsevier Science Ltd. All rights reserved.
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    Phytophthora species associated with crown and root rot of apple in Chile
    (AMER PHYTOPATHOLOGICAL SOC, 2001) Latorre, BA; Rioja, ME; Wilcox, WF
    Phytophthora cactorum, P. cryptogea, P. gonapodyides, and P. megasperma were isolated from necrotic root and crown tissues or the rhizospheres of apple trees exhibiting typical symptoms of Phytophthora root and crown rot in the Central Valley of Chile. Representative isolates of all four species were pathogenic on a variety of apple rootstocks and scions in trials conducted on excised shoots and 1-year-old MM.106 rootstock grown for 4 months in infested potting medium. P. cactorum was the most frequently isolated species and the most virulent in pot tests, although a significant Phytophthora sp.-apple genotype interaction was observed. This is the first report of any species other than P. cactorum causing root and crown rot of apple trees in Chile.
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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.