Abstract

Four types of airborne rust spores has been monitored by means of aerobiology in Central Italy between May and June. Uredospores of Puccinia, and Cronartium / Melampsora/ Melampsoridium-type; teliospores of Puccinia and Phragmidium were observed in spore traps. Spore concentration and meteorological data were correlated. Uredospore counts were increased by temperature, evaporation and solar radiation. High relative humidity, cloud cover and precipitation reduced uredospore counts. Teliospores were released by moderate and stronger air currents.

Introduction

The importance of aeromycological monitoring of plant pathogenic spores has been recognised after the great epidemics in North America caused by rusts in 1920' (Stakman & Christensen, 1946). Thereafter other trajectories have been revealed, e.g. in India (Nagarajan & Singh, 1976) between Paraguay and Argentina (Waller, 1979), from Angola to Brazil (Bowden et al., 1971), across the Tasman Sea from Australia to New Zealand (Viljanen-Rollinson & Cromey, 2002). Our knowledge about airborne spore pathway between South and Central Europe is insufficient (Brown & Hovmøller, 2002). The aim is our study to complete information of rust spore aeromycolgy in this critical geographical area.

Materials and Methods

Hirst-type air samplers (Hirst, 1952) were used to register the daily concentration of airborne spores. The samples were located in a traditional vineyard in Umbria country of Central Italy, in 1994, 1995 and 1996, between May and July. (in Brufa between 27 May and 13 June 1994; in Brufa between 05 June and 03 July 1995; in Brufa between 13 June and 24 June 1996; in Casalina between 13 June and 27 June 1991; in Ormelle between 03 June and 23 June 1996; in Torgiano between 24 May and 05 July 1993). The spore trap were placed in an instrumented tower at height of 30 m above ground level. For microscopical work we used 400X object lens of DIALUX 20 microscope. Two longitudinal transverses along the length of the silicone-coated slide were scanned to determine spore concentration of the air samples, concentration was expressed in spore/m3. The measured meteorological factors were: wind speed [m/s], wind direction, atmospheric pressure [Pa], minimum, maximum and mean temperatures - [Co], precipitation [mm], rainfall intensity [mm/s], duration of precipitation [min], cloud cover [%], relative humidity [%], presence of fog and mist, dew point [Co], evaporation [mm], number of sun hours [min]. The Spearman's Correlation Analysis was applied to clear the relations between changes of daily airborne spore concentration and the meteorological factors.

Results

Hyaline uredospores of Cronartium / Melampsora/ Melampsoridium spp. were frequent in air samples. Concentration increased by solar radiation, minimum temperature, dew point, evaporation and long drought periods. Large amounts of spores were measured when the number of sun hours appeared to be high on the 2^nd and 3^rd day before capturing (Sd-2, Sd-3). Precipitation on the 3^rd and 4^th day before observation (Pd-3, Pd-4) caused high concentration. Wind gusts (50-80 km/h) and air currents from North-East in Brufa, and from South in Torgiano had strong positive effects. Spore concentration has been reduced by cloud cover. High relative humidity on the 1^st and 2^nd day before observation (RHd-1, RHd-2) decreased counts.

Uredospore counts of Puccinia spp. correlated positively with temperature, number of sun hours, evaporation and solar radiation. High relative humidity, RHd-1, RHd-2, fog, number of rainy days, duration of precipitation had negative effect on the spore concentration. Rainstorms with strong winds removed the airspora efficiently. The presence of airborne sand particles showed positive correlation with the uredospore counts.

Puccinia teliospores were observed rarely in the monitored period. Sudden change of wind direction and wind gusts caused spore release. Phragmidium teliospore were detected only once when wind blown from South-East. The results of statistical analysis are summarized in Table 1.

Discussion

As many author noticed, wind is probably the most important factor in the spore release of Uredinales (Carter et al., 1970; Hirst, 1961; Smith, 1966; Sache, 2000). Wind gusts are effective as well (Sache, 2000). However, spore free winds should reduce spore concentration by dilution or blow-off (Hamilton, 1959). Vourinen and Helander (1995) observed the positive effect of wind speed and temperature on the spore dissemination of Melampsoridium betulinum (Fries) Kleb. Our results suggest, that previously deposited teliospores of Puccinia, or large teliospores of Phragmidium should become airborne by excessive winds. In our results relative humidity has been proved more effective than precipitation. In saturated air deposition rate of spores increased because they are heavier (Weinhold, 1955) and larger (Madelin & Johnson, 1992). Wetted surfaces acts as natural spore traps as well, thereby reducing the number of airborne spores. The positive effect of temperature and light intensity (Smith, 1966: P. graminis Pers var. tritici Eriks. & E. Henn.) should correlate with favourable wind dissemination. Dry liberation by rain droplets (the so called 'tap and puff' mechanism) mentioned as well as splash dispersal of spores (Geagea et al., 1999; P. recondita f.sp. tritici C.O. Johnson; P. striiformis Westend, Nutman et al., 1960; Bock, 1962; Hemileia vastatrix Berk. & Br., Hirst, 1961; P. graminis Pers, Carter et al., 1970; Tranzschelia discolor (Fckl.) Tranz. & Litv.). In our results there were no direct positive effects of rain. Washing- off the spores from the air in longer rains (Hamilton, 1959; Puccinia spp.) or in intensive rainstorms (Sache, 2000) has been proved again.

Acknowledgemets

The authors are grateful to professor Giuseppe Frenguelli, Emma Bricchi and Emma Tedeschini from the University of Perugia. This work was supported by a grant from the Hungarian Grant Committee (MÖB).

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