Epidemiology of dark leaf spot caused by Alternaria brassicicola and A. brassicae in organic seed production of cauliflower

• Published in: Plant pathology Vol. 59; no. 2; pp. 358 - 367
• Main Authors: Köhl, J, van Tongeren, C.A.M, Groenenboom-de Haas, B.H, van Hoof, R.A, Driessen, R, van der Heijden, L
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-04-2010; Blackwell Publishing Ltd; Blackwell; Wiley Subscription Services, Inc
• Subjects: Alternaria brassicicola; Biological and medical sciences; Brassica oleracea var. botrytis; dark leaf spot; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; organic farming; organic production; Phytopathology. Animal pests. Plant and forest protection; seed quality; TaqMan-PCR; Netherlands; Plant pathology; Vegetables; Plant pathogen; Alternaria brassicicola; Epidemiology; Fungi; Cruciferae; Dicotyledones; Quality; Angiospermae; Cauliflower; Fungi Imperfecti; C3-Type; organic farming; Brassica oleracea var. botrytis; Production system; Vegetals; Botrytis; seed quality; Seed production; Plant leaf; Alternative agriculture; Polymerase chain reaction; Brassica oleracea; Vegetable crop; Organic agriculture; Seed; Vegetative apparatus; Spermatophyta; dark leaf spot; Molecular biology; TaqMan-PCR
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1111/j.1365-3059.2009.02216.x

In organic seed production of Brassica vegetables, infections by Alternaria brassicicola and A. brassicae can cause severe losses of yield and seed quality. Four field experiments with or without artificial inoculation with A. brassicicola were conducted in organically managed seed-production crops of cauliflower cv. Opaal RZ in 2005 and 2006 in the Netherlands. The development of A. brassicicola and A. brassicae on pod tissues and developing seeds was followed and seed quality was assessed. Alternaria brassicicola was externally present on 1·2% of the seeds 14 days after flowering and observed internally within 4 weeks after flowering. In both seasons, seed colonization by the pathogen increased slowly until maturation but sharply increased during maturation. A similar pattern was found for the colonization of pod tissues by A. brassicicola as quantified by TaqMan-PCR. The incidence of A. brassicicola on mature seeds reached 70-90%. Internal colonization was found for 62-80% of the seeds. External and internal seed colonization by A. brassicae was much lower, with incidences below 3%. The quality of harvested seeds was generally low, with less than 80% of seeds able to germinate. Seed quality was not affected by warm water treatments. It was concluded that A. brassicicola and A. brassicae have the potential to infect pods and seeds soon after flowering. For the production of high quality seeds, producers must prevent such early infections. Therefore, new control measures are needed for use in organic cropping systems.