Patterns of airborne conidia of Stemphylium vesicarium, the causal agent of brown spot disease of pears, in relation to weather conditions

Abstract

Seven-day volumetric spore samplers were installed in pear orchards of northern Italy, in the years between 1993 and 2002, and operated continuously during the development of brown spot epidemics (mid-April-mid-August), caused by Stemphylium vesicarium. Aerial concentration of conidia was recorded at 2 h intervals to study their diurnal and seasonal patterns and the influence of weather conditions. The diurnal periodicity of aerial conidia showed a peak around midday and low counts in the dark. The increase in spore concentration was significantly correlated with the reduction of relative humidity and wetness in early morning, and the increase of wind in late morning and afternoon. Conidia of S. vesicarium became easily airborne to form a regular component of the air-spora in pear orchards, while ascospores were caught only sporadically. Differences between years concerned total spore counts and numbers of peaks (defined as days with more than 30 conidia/m 3 air per day). Periods with highest spore counts occurred in late-May to early-June (in 2 years), mid to end of June (5 years), or after midJuly (3 years). There was a significant correlation between spore peaks and days with favourable weather conditions, defined as days with air temperature between 15 and 25°C and high humidity, particularly a wet period longer than 10 h. Occurrence of one or more consecutive days with favourable weather conditions determined an increase in the airborne concentration of conidia, which usually lasted some days and then decreased.

Aerobiologia de Cercospora kikuchii

“…Desse modo, o entendimento dos fatores que influenciam no desenvolvimento das doenças é essencial para tomada de decisões para o manejo adequado. ROSSI et al (2005) verificaram que o aumento da concentração de esporos de Stemphylium vesicarium em área com cultura de pêra foi correlacionado com umidade relativa do ar, período de molhamento foliar no início da manhã e com o aumento do vento no final da manhã e à tarde. Segundo STEPALSKA & WOLEK (2005), trabalhos realizados na Polônia indicaram que a temperatura é a variável mais influente na concentração aérea de esporos de Alternaria, Botrytis e Cladosporium, com correlações significativas e positivas.…”

Pathogenicity of Stemphylium vesicarium from different hosts causing brown spot in pear

“…Ascospores are found on fallen pear leaves on orchard floors only during early spring, but epidemics usually start in summer (Llorente and Montesinos 2006). Since only airborne conidia are detected in spore traps during summer (Rossi et al 2005a), conidia may be the prevalent primary inoculum of the disease. Conidia are rarely observed in lesions on affected pear leaves during summer.…”

Sources and seasonal dynamics of inoculum for brown spot disease of pear

“…1d-f) even though weather conditions were less favourable for sporulation. In July-September, RH, rainfall and number of rainy days were lower in 2004 than in the other 2 years (Table 3); the number of days with favourable conditions for sporulation estimated according to Rossi et al (2005bRossi et al ( ) were 12, 23 and 26 in 2003Rossi et al ( , 2004Rossi et al ( and 2005 Pathogenicity of S. vesicarium strains Forty strains of S. vesicarium were obtained from the spore traps in 2006: 11 from type I inoculum source, 19 from II, 6 from III and 4 from IV; no strains were obtained from the uninoculated plots (V). All these strains caused brown spot symptoms on the inoculated leaves of cv.…”

“…Ascospores are released from February to May or early June (Llorente et al 2003), but disease symptoms usually first appear from mid-June (Ponti et al 1982), when few or no ascospores are present in the orchard air (Picco et al 1996). In this period, conidia are usually abundant and continue to be airborne during the pear-growing season (Rossi et al 2005b), though sporulation rarely occurs on infected pear tissues (Maccaferri et al 2003). Recent studies (Rossi et al 2005a) demonstrated that S. vesicarium strains are able to colonize dead tissues of herb plants as saprophytes and to produce abundant ascospores and conidia that are capable of infecting pear.…”