Wind dispersal of Puccinia horiana

Abstract

About 1964 in several countries of Western-Europe Puccinia horiana P. Henn. was recorded for the first time in chrysanthemums, Chrysanthemum morifolium. In all cases it could be established that the rust was imported with infected cuttings (Boerema and Vermeulen, 1964;Melder, 1964;Jorgensen, 1964;Baker, 1967). During the field inspection performed by the Plant Protection Service we found outbreaks which could not be explained by dispersal with infected cuttings. We therefore collected information on the dispersal of inoculum.In 1965 we visited a plot with chrysanthemums severely attacked by P. horiana; we also found the symptoms in the adjacent plots (Fig. 1). The following observations were made: (1) Infected plants were almost exlusively found in the sector east of the attacked plot, over a distance of up to 350 m. At greater distances there were no chrysanthemums.(2) The greater the distance from the attacked plot, the less was the percentage of infected chrysanthemum plants. (3) Close to the attacked plot, infection was found all over the plants. At a greater distance from the source, infection was usually confined to the upper parts of the plants. (4) In glasshouses in the same sector, infection was found mainly under the ventilation windows. In 1966 we made the following observations: (1) About 7 August a heavily infected crop in a glasshouse was destroyed. A fortnight later a plant with sporulating sori was found outside the glasshouse in a corner with frequent whirlwinds. (2) In another locality, at a nursery close to an infected crop, a mild infection was found especially at a place outside with whirlwinds. (3) In a third locality, at two nurseries east of an infected crop at distances of about 500 and 700 m, respectively, (Fig. 2), we found an infection at places with whirlwinds. Between the infected crop and the two eastward nurseries, no chrysanthemums were cultivated. (4) In several other places we saw that nearly all infections, clearly unrelated to infected cuttings, were found east of the infected crop. These data show that there is a horizontal gradient of infection from an attacked plot. The gradient tapers out in down-wind direction. This direction usually is east because 124

A pattern in the appearance of cucumber powdery mildew in Dutch glasshouses

“…Since glasshouses are not so air-tight as has often been suggested, conidia can probably leave and enter the glasshouses fairly easily, as has been reported for other pathogens (Frinking and Scholte, 1983;Zadoks, 1967;Zandvoort, 1968). The occurrence of first mildew lesions on places with much air circulation was not restricted to districts with a high crop density, but was also observed in districts where crops were situated several kilometers apart.…”

Influence of environmental conditions in a glasshouse on conidia ofBotrytis cinerea and on post-harvest infection of rose flowers

“…Leakage of air in a modern glasshouse through openings other than ventilation windows is strongly influenced by wind-speed outside [Fernfindez and Bailey, 1992] and is for example 0.028 (change of total amount of glasshouse air per hour) at a wind-speed outside of 1 m/s [Groen, 1988]. Zandvoort [1968] showed that inoculum of Puccinia horiana can as readily enter the glasshouse as it escapes the glasshouse, apparently by way of ventilation windows and other openings. Frinking [1991] claimed a continuous exchange of air between the glasshouse and its outside environment, because of wind speeds outside the glasshouse, which normally exceed those within the glasshouse, and because of differences in temperature.…”

“…Airborne epidemics often start with the entry of one or more fungal spores from the outside environment [Frinking, 1991]. Zandvoort [1968] showed that inoculum of Puccinia horiana can as readily enter the glasshouse as it escapes the glasshouse, apparently by way of ventilation windows and other openings. The same is suggested by Schepers [1984] for conidia of Sphaerotheca fuliginea.…”

Scientific Opinion on the risk to plant health posed byPuccinia horianaHennings for the EU territory, with the identification and evaluation of risk reduction options

“…Wind may transport basidiospores for at least 700 metres (Zandvoort, 1968) and their germinability may be maintained by high RH (one hour at 90 % RH, according to Firman and Martin, 1968).…”

“…Light does not affect germination of teliospores or basidiospores, according to Firman and Martin (1968), while Yamada (1956) observed a negative effect of light on teliospore germination but not on basidiospore germination. Basidiospores are dispersed by wind, which can transport them at least 700 metres (Zandvoort, 1968) and possibly several kilometres (De Backer, 2012). Successful aerial transport needs to occur under conditions of high RH, as basidiospores lose their germinability after five minutes at RH values of 80 % and after one hour at RH values of 90 % (Firman and Martin, 1968).…”