Seed Tent cover Leaf gray mold1 Leaf graymold2 Uninfected seed open 0.19 53 Tented 0 0.95 Infected seed open 5.61 11.3   0 3.5 cv of mean3 Tented 13% 22%

1Disease was expressed as number of lesions per plant. It was analysed on log scale: main effects and interaction significant (P<0.001, df 1,6). Block and plot variances not significantly larger than plant variance. B. cinerea. 2Disease expressed as number of lesions per plant. It was analysed on log scale: main effects of seed source, P<0.006 (1,6 df); tenting P<0.001. Interaction P=0.4. Blocks did not differ more than expected from plot-plot variation, but this was significantly more than plant-plant variation (P<0.001; 6108 df). 3The coefficient of variation from sem on log scale; the variability applies to any mean in the column closer, the main effect differences were highly significant (P=0.006 for seed source, P<0.001 for tenting) and the interaction was no longer significant (P=0.4).

Table 1: Visual assessment of plant B. cinerea. Samples were taken from the centre 1 m2 subplot of plots of lettuce grown from clean (symptomless) or infected seed sources and covered or left open until then. Ten plants per subplot were assessed. Back transformed mean values per plant are given.