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AEROBIOLOGY OF ALTERNARIA SPORES IN MURCIA AREA (SE SPAIN)
AEROBIOLOGY OF ALTERNARIA SPORES IN MURCIA AREA (SE SPAIN) M MUNUERA GINERl and JS CARRI6N GARCiAl lDepto. Biologia Vegetal, Fac. Biologia, Universidad Murcia, 30100 Espinardo (Murcia), Espaha Background and objectives Aiternaria is a well-known cosmopolite fungus genus including ca. 50 species. Most of them are obligate plant parasites on crucifers, cereals and other vegetables, provoking crop diseases and lots of economic losts every year throughout the world. Like other fungus, Aiternaria disperses their spores by releasing them into the turbulent airstreams of the atmosphere, allowing the spores to be distributed long far away from their source. Sporulation and dispersal is depending on biological, climatic and physical processes and within plant pathology numerous efforts are made every day to find their patterns. The aim of this work was to find out (on the basis of 2 years data) correlations with meteorological factors and annual, seasonal and hourly distribution patterns in Aiternaria airborne spores that could be used in preventing crops invasions in addition with the previous knowledge about optimum growth temperatures and relative humidity ranges in Murcia area (SE Spain) [1]. Materials and methods From 1 March 1993 to 28 February 1995 a Burkard volumetric 7-day recording spore trap was operated at about 19 m above ground level, on the exposed flat roof of the Veterinary Faculty. Slides were prepared following standard aerobiological methods and examined by light microscopy. The data, expresed as numbers of spores/m3 of air, were obtained by counting all Aiternaria spores on four longitudinal transects. Those daily slides spoiled by insects were ignored. Meteorological data were obtained from the Institute Nacional de Meteorologia in Murcia, located 1 km from the sampling site. The relationships between Aiternaria spores and weather variables were explored by the Spearman rank correlation coefficient method because the nonnormal distribution of spore counts. Results and conclusions Overall quantities of 10821 and 6276 sporelm3 were obtained from 1 March 1993 to 28 February 1994 and from 1 March 1994 to 28 February 1995 respectively (first and second period in forward). The real content was probably higher having in mind that, because its relative large spore volume, Aiternaria is believed to be strongly underrepresented in the spore counts at roof level [2]. The mean daily concentration varied between periods: 32 spore/m3 for the first period and 18 sporelm3 for the second one. A maximum (182 spore/m3) was reached at 10 June 1993. For the whole period mean daily concentration was 25 sporelm3. Seasonal variations showed the highest concentrations during autumn (about 40% of the total). The lowest concentrations were registered in winter (about 7-8%). Summer presents higher concentrations than spring but in both cases ranging about 25-30%. The patterns observed in the monthly variation were similar between the periods (with lower levels for the second one) and peaked twice each year: in May-June and in September-October, with a fall in summer because high temperatures and low relative humidity. Few Aiternaria spores were found during winter, when mean minimum temperature was clearly (2-30C) below the minimum of the optimum (13-20"C). Throughout the day, low concentrations were found during night with minimum at dawn and increasing constantly up to reach the maximum from 14h to 19h (Spanish official time). Mathematical analyses showed very significant correlations (p<0.001) between spore concentrations and meteorological factors: positive with temperatures during spring and autumn; negative with atmospheric pressure during autumn; positive with evaporation except in winter; positive with wind velocity during autumn. Other correlations (p<0.01) are noticeable: positive with minimum temperature in winter; positive with wind direction in summer (SW), autumn (NE and SE) and winter (NE); negative with wind direction in spring (NW), summer (NE), autumn (SW) and winter (SW and NW). References 1. Munuera M, Carri6n JS. 1995. International Journal of Biometeorology 38, 176-179. 2. Hjeimroos M. 1993. Grana 32, 40-47.