A computer program using the language and statistical procedures available from SAS (Statistical Analysis System) was written in order to identify the most highly correlated meteorological factors with the incidence of wheat head blight (caused by Fusarium graminearum Schwabe) at Pergamino, in the humid pampeana region. Applying linear regression techniques, different models from simple up to a maximum of three independent variables were fitted to the data (1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990). The meteorological variables were processed in a time segment beginning eight days prior to the heading date (50% of emerged ears) and finishing when 530 degree days were accumulated (26-32 days). The number of two day periods with rainfall and relative humidity >81% in the first day and relative humidity >78% in the second (NPPRH) was the variable that showed the strongest association with disease incidence (FI) (R 2 = 0.81). After examining the models in several ways (1t 2, Adjusted R 2, PRESS statistic), two equations were selected: FI% --20.37 + 8.63 NPPRH -0.49 DDXNT (R 2 = 0.86) and FI% = 16.39 + 5.43 NPPRH -0.45 DDXNT + 2.95 DPRH (R 2 = 0.886), in which DDXNT represents the daily accumulation of the residuals resulting from subtracting 9 to the minimum temperature values (<9 ~ C) and the exceeding amounts of maximum temperatures from 26 * C and DPRH is the number of days with precipitation and relative humidity greater than 83%. Successful local predictions of incidence of scab for the years 1991-1993 (reserved for validation purposes) were achieved using both equations.
Barley is an important malting crop extensively cultivated in the province of Buenos Aires (AR). In 1992, an unusual disease was detected with a prevalence of 8% on 36 commercial fields examined in this province. The pattern of the disease, the characteristics of the pathogen and the test for pathogenicity indicated that the causal agent was Pseudoseptoria donacis.
Asian soybean rust (ASR) is a very important disease caused by Phakopsora pachyrhizi. The disease has emerged as a major threat to soybean production in South America since 2001. During the 2003-2004 growing season, P. pachyrhizi spread rapidly throughout most soybean-growing areas of northwestern and northeastern Argentina (1). One widespread naturalized host in the northeastern part of the country is kudzu (Pueraria lobata). Plants of severely infected kudzu were sampled during January 2005 in Cerro Azul (29°29′S Misiones Province) to quantify P. pachyrhizi infection and morphologically characterize the fungus in leaves. The number of lesions, uredinia per cm2, and uredinia per lesion were recorded from the undersides of 50 leaflets that were visually showing rust symptoms. The average number of lesions and uredinia per cm2 was 14 (4 to 22), and 24 (5 to 78), respectively. The number of uredinia per lesion was 3 (1 to 10). Twenty leaflets from the lower canopy averaged 55 (42 to 78) uredinia per cm2. The average size of urediniospores was 18.4 μm wide (12.5 to 22.5) and 22.7 μm long (17.5 to 26.3). Although important epidemics of ASR have not been registered on soybean crops in January (2) because of adverse conditions, the fungus was observed on kudzu plants. To our knowledge, this is the first report of morphologic and pathometric characterization of P. pachyrhizi on kudzu in Argentina. References: (1) M. A. Carmona et al Plant Dis. 89:109, 2005. (2) SINAVIMO, Sistema Nacional Argentino de Vigilancia y Monitoreo de plagas. Roya de la soja: Resultados de la campaña 2004-2005. On-line publication. SENASA, 2005.
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