Abstract
The A2 mating type ofPhytophthora infestans was first reported in the United States in 1990. Concurrently,P. infestans strains resistant to metalaxyl ere found in the Pacific Northwest. Collaborative surveys were undertaken during 1991–1993 to investigate the frequency of occurrence of A2 mating types and metalaxyl resistant strains in populations ofP. infestans isolated from outbreaks of late blight in potato and tomato crops in North America.In vitro testing indicated that isolates from the northeastern U.S. and Atlantic Canada were primarily (52/55) metalaxyl sensitive and all were A1 mating types. Among 85 isolates from late blight epidemics in Florida and Texas, greater than 61% were both metalaxyl resistant and A2 mating type. Metalaxyl resistance and A2 mating types were identified also in a few tomato isolates from North Carolina. Although the majority of 134 isolates from the Pacific Northwest (British Columbia and Washington) were metalaxyl resistant, only 2 isolates from Washington were A2 mating types. Among 111 isolates from 2 sites in central Mexico, 63% and 77% were both metalaxyl resistant and A2 mating types. The data indicate also a higher frequency of metalaxyl resistance in A2 isolates, than in A1 isolates, among isolates from Florida and Texas. Highest metalaxyl resistance levels were found, however, in A1 isolates from California, where no A2 isolates were recovered.
Compendio
El tipo reproductivo A2 de Phytophthora infestans fue reportado por primera vez en los Estados Unidos en 1990. Simultáneamente, se encontraron en el noroeste del Pacífíco variantes de P infestans, resistentes al metalaxyl. Durante 1991–1993, se llevaron a cabo encuestas colaborativas para investigar la frecuencia conque se presentan los tipos A2 y las variantes resistentes al metalaxyl en las poblaciones de P. infestans aisladas, en las epidemias de tizón tardío, de los eultivos de papa y tomate en Norteamérica. La pruebas in vitro indicaron que los aislamientos del noreste de los Estados Unidos y de la zona canadiense del Atlántico fueron principalmente (52/ 55) sensibles al metalaxyl, perteneciendo todos ellos al tipo reproductivo A1. Entre 85 aislamientos de epidemias de tizón tardío en Florida y Texas, m as de 61 % fueron resistentes al metalaxyl y del tipo reproductivo A2. Se identificaron también la resistencia al metalaxyl y los tipos reproductivos A2 en algunos aislamientos de tomate en Carolina del Norte. Aunque la mayoría de 134 aislamientos del noroeste del Pacífico (Columbia Británica y Washington) fueron resistentes al metalaxyl, sólo dos aislamientos de Washington fueron de los tipos reproductivos A2. Entre 111 aislamientos de dos lugares del centro de México, 63% y 77% fueron tanto resistentes al metalaxyl como de los tipos reproductivos A2. Los datos también señalan una mayor frecuencia de resistencia al metalaxyl en los aislamientos A2 que en los A1 efectuados en Florida y Texas. Sin embargo, se encontraron niveles más altos de resistencia al metalaxyl en los aislamientos A1 de California, donde no se recuperaron aislamientos A2.
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Deahl, K.L., DeMuth, S.P., Sinden, S.L. et al. Identification of mating types and metalaxyl resistance in North American populations ofPhytophthora infestans . American Potato Journal 72, 35–49 (1995). https://doi.org/10.1007/BF02874378
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DOI: https://doi.org/10.1007/BF02874378