Effects of habitat fragmentation on choke disease (Epichloe bromicola) in the grass Bromus erectus

K. Groppe et al., Effects of habitat fragmentation on choke disease (Epichloe bromicola) in the grass Bromus erectus, J ECOLOGY, 89(2), 2001, pp. 247-255
Citations number
Categorie Soggetti
Journal title
ISSN journal
0022-0477 → ACNP
Year of publication
247 - 255
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1 The fungal endophyte Epichloe bromicola causes choke disease on Bromus er ectus, thereby suppressing maturation of host inflorescences. We conducted a 3-year field experiment to investigate the effects of small-scale habitat fragmentation on the occurrence of choke disease in three calcareous grass lands in the Swiss Jura Mountains, where, overall, 4.3% of all flowering ti llers had diseased inflorescences. 2 The number of diseased B. erectus plants (presumed genets), the number of tillers with diseased inflorescences, and the number of tillers with healt hy inflorescences were counted over 3 years, but healthy tillers could not be allocated to particular genets. Each of 12 blocks contained one large (4 .5 x 4.5 m), one medium (1.5 x 1.5 m) and two small (0.5 x 0.5 m) fragments and corresponding control plots. The percentage of tillers in the plots th at were infected but did not show disease symptoms (asymptomatic plants) wa s estimated in the final year of the study using a diagnostic polymerase ch ain reaction. On average 1.7% of all tillers without disease symptoms were infected. 3 There were significantly more diseased plants in fragment than in control plots, particularly in small fragment plots or in the third year of the st udy, indicating that disease incidence in the host plant increased after fr agmentation if assessed at the level of the genet population. This was prob ably due both to a switch of genets from the asymptomatic to the symptomati c state and to increased horizontal transmission of the disease in fragment s. 4 The increase in the number of flowering tillers with diseased inflorescen ces was outweighed by that in the number of tillers with healthy infloresce nces. Disease incidence was therefore decreased by fragmentation if assesse d at the level of the host flowering tiller population. The effect on healt hy plants was probably due to beneficial abiotic edge effects following fra gmentation. 5 Plot size affected fragmentation response, with the largest increases in small, followed by medium and large fragments. Similarly, the strength of f ragmentation responses increased through time over the 3-year study period. 6 Significant site to site and year to year variation in the number of dise ased plants and in the number of tillers with diseased inflorescences sugge sted that separate experiments with replication within site and year would have yielded a series of interesting but individually different results. On ly by repeating the experiments at several sites and over several years was it possible to obtain the general results reported in the previous points.