**4.3 Effects of temperature and wetness duration on conidial germination** *in vitro*

Conidial germination was evaluated and observed at all 11 temperatures, except 32°C (**Figure 5A**). Conidia did not germinate within 2 h at all temperatures. At 4, 8, 14, 18, 20, 22, 24, and 28°C, germination started at 4 h. At 6 h, the germination rates at 14, 18, 20, 22, and 24°C all exceeded 30%. At 18 h, the germination rates at 14, 18, 20, 22, and 24°C all exceeded 90%. The highest germination rate was observed at 20°C (97.16%). At 24 h, all conidia at 18, 20, and 22°C had germinated. The germination rate exceeded 90% at 8, 14, and 24°C. Thus, temperatures above 28°C and below 4°C are not conducive to conidial germination, with the optimal temperature for germination between 14 and 22°C.

*Cultivation Practice of Chinese Medicinal Herbs DOI: http://dx.doi.org/10.5772/intechopen.104859*

#### **Figure 5.**

*Effects of temperature and wetness duration on conidial germination in vitro. (A) Average germination rate of conidia at 11 different temperatures and different time points. (B) Average germination rate of conidia under seven different wetness durations.*

#### **Figure 6.**

*Effects of different leaf wetness durations on the occurrence of round spot disease. (A) Incidence and (B) disease index of round spot disease for different leaf wetness durations. \*P < 0.05, \*\*P < 0.01; n = 3, ns: no significant difference.*

Free water is a key factor for conidial germination. The effect of leaf wetness duration was first investigated *in vitro*. When the wetness duration was less than 2 h, conidia could not germinate (**Figure 5B**). Between 2 and 24 h, the germination rate increased with increasing wetness duration. All conidia were germinated when a free water film was present for 24 h. Even at 99% relative humidity, in the absence of free water, the conidia did not germinate.

#### **4.4 Effect of** *P. notoginseng* **leaf wetness duration on conidial infection**

To evaluate the effect of leaf wetness duration on conidial infection, in the greenhouse experiment, round spot disease incidence was investigated 10 days after inoculation. When the leaf wetness duration was shorter than or equal to 8 h, no

disease spots appeared on the *P. notoginseng* leaf surface*.* When the leaf wetness duration was longer than or equal to 12 h, the incidence and disease index of round spot disease increased according to the leaf wetness duration (**Figure 4A** and **B**). Round spot disease incidence and disease index at a wetness duration of 24 h were 55.56% and 32.78, respectively, and were significantly higher than those at a wetness duration of 12 h and 18 h (**Figure 6**).
