Temperature and effects of seed-borne Botrytis cinerea or Alternaria linicola on emergence of linseed (Linum usitatissimum ) seedlings

Experiments were done at temperatures from 5 to 20 degrees C to investigate the effects of infection of linseed seed (cv. Antares) by Botrytis cinerea or Alternaria linicola on seedling emergence and to study transmission of the pathogens from seed to seedlings. In one experiment with freshly harvested seed, the maximum percentage emergence decreased linearly as the incidence of B. cinerea in seed increased from 0 to 83% at 18 degrees C day/12 degrees C night temperatures. In another experiment, the decrease in percentage emergence of seed associated with infection by B. cinerea, the transmission of the pathogen to seedlings to produce disease symptoms on their hypocotyls and the incidence of post-emergence death all increased as temperature decreased from 20 to 5 degrees C. However, the decrease in percentage emergence of seed associated with infection by A. linicola and the transmission of the pathogen to seedlings to produce cotyledon lesions both increased as temperature increased from 5 to 20 degrees C. There was little effect of either pathogen on the time from sowing to 36% of maximum emergence, which decreased with increasing temperature. In a subsequent experiment at 10 degrees C comparing seed infected with B.cinerea or A. linicola, using the same seed sources as in the previous experiments, infection by A. linicola decreased emergence more than infection by B. cinerea, even though the incidence of A. linicola in the seed was smaller. Analyses of position and parallelism suggested that regressions of maximum percentage emergence (logit-transformed) against temperature were fitted best by non-parallel lines for seed infected by B. cinerea or A. linicola.