Effects of isolate virulence and host susceptibility on development of early blight (Alternaria solani) on tomato*

Abstract

Early blight of tomato (Lycopersicon esculentum) caused by Altemaria solani has the potential to become one of the most serious diseases throughout the tomato-producing regions of Greece.Controlled environment experiments were conducted to study the virulence of A. soluni isolates and the susceptibility of commercial tomato cultivars and hybrids to early blight. The isolates used, derived from naturally infected tomato plants during the period 1997/1998, differed significantly (P>O.O5) in the rate of mycelial growth as well as in their ability to sporulate in vifro. No correlation (R2 = 0.33) was found between mycelial growth and conidia production.Isolates of A. solani were virulent to young tomato plants (cv. Ace 55VF), although they differed significantly (P >0.05) in the intensity of symptoms produced on leaves, stems, petioles and flowers. Defoliation was linearly related (R2 = 0.87) to the percentage of leaf area with symptoms. Twenty-three tomato cvs. or F, hybrids were evaluated for their susceptibility to early blight. The cultivars or hybrids were arbitrarily categorized as immune, highly tolerant, tolerant, moderately tolerant, susceptible and highly susceptible based on a percent disease index range: 0%, 1-9%, 10-24%, 25-49%, 50-74% and 75% or more respectively. None of the cultivars or hybrids tested was immune or tolerant to A. soluni infection.

Review: Holistic pest management against early blight disease towards sustainable agriculture

“…The optimum temperature for EB epidemics is in the range of 20–30 °C 18 . As few as 3 hours of continuous leaf wetness between 21 and 25 °C is sufficient for EB lesion formation 19 and at 24 ± 2 °C, the infection appears within 4–6 h of leaf wetness 20 . There is variability with different geographic regions, with an optimal temperature in temperate regions of 22–28 °C, while the most conidia production under tropical conditions occurs at 29–35 °C 21 .…”

“…At high humidity on leaf surfaces, especially after dew, conidial initiation occurs. A duration of 4–6 hours of leaf wetness after inoculation with conidia is sufficient to ensure the onset of EB 20 . The link between lower temperature and higher RH during the night is favourable for the development of sporulation 18 ; the new spores are released during the day when the temperature increases.…”

“…Using a small component of the FAST model (hourly leaf wetness and temperature), disease severity values (DSVs) are determined. 82 The value range of the DSVs 15 , 16 , 17 , 18 , 19 , 20 defines the pest control schedule. Subsequent treatment is conducted with a pesticide, originally arranged with chlorothalonil .…”