Microcycle conidiation in Cercospora zeae-maydis

• Published in: Phytopathology 2003-02, Vol.93 (2), p.193-199
• Main Authors: Lapaire, C.L, Dunkle, L.D
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cercospora zeae-maydis; conidia; droplets; dry environmental conditions; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; gray leaf spot of maize; humidity; infection; leaves; nitrogen; nutrient requirements; pathogenicity; Pathology, epidemiology, host-fungus relationships. Damages, economic importance; Phytopathology. Animal pests. Plant and forest protection; plant pathogenic fungi; secondary conidia; spore germination; sporulation; trichomes; Variation, races, biotypes, parasitic specialization, genetics; water; Zea mays
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/PHYTO.2003.93.2.193

Conidia of Cercospora zeae-maydis are the primary inoculum causing gray leaf spot of maize. On nutrient-deficient substrates, but not on water on the leaf surface, conidia germinate and develop secondary conidia on conidiophores produced from germ tubes or conidial cells. A population of conidia increases its numbers more than twofold by 2 days on the surface of a water droplet and by fourfold on trichomes. This microcycle conidiation is suppressed by hydrogen peroxide and ammonium compounds but not by nitrate compounds, amino acids, or simple sugars. Microcycle conidiation is sensitive to α-amanitin and cycloheximide, suggesting that new RNA and proteins must be synthesized. Upon transfer from a humid to a dry atmosphere, secondary conidia and conidiophores dehydrate and collapse. Mature, dehydrated, secondary conidia are liberated by wind speeds approximately one-third those required to liberate hydrated conidia. The dispersed secondary conidia can rehydrate and germinate normally. Because this microcycle conidiation occurs at the expense of endogenous reserves, the ability to produce secondary conidia is lost after four successive cycles without a period of growth on nutrient media. This alternative method of maintaining inoculum potential during periods of fluctuating relative humidity may have epidemiological consequences when primary conidia fail to infect.