Effect of Cryptomycina pteridis on Pteridium aquilinum

Abstract

Pteridium aquilinum, noninfected and naturally infected with Cryptomycina pteridis, was studied in western South Dakota from 1990–1992. Time of frond emergence in 1990 and 1991 was not significantly different between fronds in noninfected plots and fronds in infected plots. Initial P. aquilinum populations in noninfected plots were significantly higher than populations in infected plots (P = 0.01), but the fungus did not significantly reduce populations in infected plots during the study. Frequency of infected fronds increased in infected plots. In infected plots mean heights of noninfected fronds were not significantly different from infected fronds except in 1990 and 1992 (P = 0.05) at the Big Hill plot where potassium levels were limiting. Biomass from noninfected and infected plots, and biomass from noninfected and infected fronds in infected plots were not significantly different. Stipes of infected fronds were significantly thicker than stipes of noninfected fronds (P = 0.0001). Infected fronds were brittle. Brittle frond texture and fungal stromatal development were strongly correlated (r = 0.9295-0.9701).

The fungus grew in and between mesophyll cells of pinnules and formed subepidermal stremata in substomatal cavities. The fungus was commonly found in the cortex of the stipe, rachises, and costae, and in vascular bundles of rhizomes. Cells not infected or adjacent to infected cells appeared normal.

Macroconidia inoculated to transplanted bracken plants were not infective, but after ascospores were inoculated to fronds small necrotic lesions formed from which stromata and macroconidia developed. Infections remained localized and the systemic nature of naturally-infected bracken did not develop. Cryptomycina pteridis is compatible with its host and could be considered an endophyte of bracken. The fungus would not be an effective biocontrol agent for bracken.

Key Words:

• biocontrol
• Cryptomycella pteridis
• endophyte