Phenotypic variability of Leptosphaeria lindquistii (anamorph: Phoma macdonaldii), a fungal pathogen of sunflower

• Published in: Plant pathology 2000-04, Vol.49 (2), p.227-234
• Main Authors: Roustaee, A, Costes, S, Dechamp-Guillaume, G, Barrault, G
• Format: Article
• Language: English
• Subjects: aggressiveness; ascospores; asexual reproduction; Biological and medical sciences; black stem; Fundamental and applied biological sciences. Psychology; fungal anatomy; fungal diseases of plants; Fungal plant pathogens; fungal spores; geographical variation; growth; Helianthus annuus; Leptosphaeria; Life Sciences; phenotype; Phoma; Phytopathology and phytopharmacy; Phytopathology. Animal pests. Plant and forest protection; pigmentation; plant pathogenic fungi; provenance; pycnidia; pycniospores; spore germination; temperature; Variation, races, biotypes, parasitic specialization, genetics; Vegetal Biology
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1046/j.1365-3059.2000.00451.x

Growth of 17 isolates of Phoma macdonaldii, the causal agent of sunflower black stem, was investigated for response to pH and temperature, and for morphology and asexual morphogenesis (pycnidiogenesis and pycnidium size). For all isolates, the optimum pH for growth was between 4 and 5, and the optimum temperature varied between 20 and 30°C and radial growth was slowest at 5 and 35°C. Significant differences in the number and size of pycnidia were observed between isolates. Pycniospore germination was investigated under various conditions in five isolates chosen for their geographical origins, pigmentation, optimum growth temperature and pycnidiogenesis. Increasing the concentration from 106 to 107 pycniospores per mL decreased the germination rate. The optimum temperature for pycniospore germination varied between 15 and 30°C, depending on the isolate, and the optimum and maximum pH values were 5 and 7, respectively. The optimum and minimum relative humidities allowing pycniospore germination were 100 and 95%, respectively. Pycniospore germination was photo‐independent. An artificial inoculation method was developed and the aggressiveness of the pathogen was assessed on a susceptible sunflower cultivar, using a 1–9 scale that integrated the percentage of necrotic area on the cotyledon petiole at the stage when the first pair of leaves was fully developed. Significant differences in aggressiveness were observed among the 17 isolates. The parameters investigated clearly suggest the occurrence of a wide phenotypic variability in Phoma macdonaldii.