The degree of protection, in terms of the percentage reduction in
the number of disease lesions, is displayed in Table 1. No significant
difference (p < 0.05) was detected between the B. subtilis HK-CSM-
1 and ITA treatments. The TSB control also displayed a protective
effect (p < 0.05) compared with the control, but lower than that of
B. subtilis HK-CSM-1.
Anthracnose infection processes can be divided into two stages,
referred to initially as biotrophs and later switching to necrotrophs.
The first biotrophic stage involves spore germination and the
formation of an appressorium, then penetration into plant tissues
by a thin penetration peg. In the second necrotrophic stage, the
invaded hypha is developed in the plant tissues, resulting in death
and collapse to form a sunken area [10,11]. To verify the attenuation
of disease symptoms, we also surveyed the differences in size
of anthracnose lesions. Interestingly, as displayed in Table 1,
treatment with B. subtilis HK-CSM-1 was not significantly different
from the control in terms of lesion size (area). However, the disease
severity was significantly reduced in plants treated with
B. subtilis HK-CSM-1 compared with the controls. This suggests
that B. subtilis was able to inhibit virulence at the penetration
stage, but not at the tissue invasion stage. This implies that
treatment during the penetration stage is critical in protecting
against anthracnose.
Lastly, we investigated the area of the lesions as a percentage of
the total leaf area, which is equivalent to disease severity. As shown
in Fig. 3 and Table 1, there was no significant difference in the
control of anthracnose between B. subtilis HK-CSM-1 and ITA
(p < 0.01). Furthermore, the percentage of leaf area covered by
lesions indicated significant linear correlation (r ¼ 0.95038,
p < 0.05) with the number of lesions. This again suggests that the
penetration stage is critical in the effective control of anthracnose
in ginseng. These observations also confirm the veracity of visual
assessments.