BbHet2 had the highest thermotolerance among the isolated colonies when exposed to 45 °C for 30–120 min (F3,120 = 3460.0, P < 0.001) (Fig. 3). At 60 min exposure, BbHet2 conidia had 60.7% germination, compared with conidia of ERL1578 (14.0%), and conidia of ERL1576 and BbHet1 (< 5.0%). Control (non-exposed conidia) had > 95% germination in all the colonies. Median lethal time (LT50) of BbHet2 conidia was 97.4 min (95% confidence level: 94.3–100.6) at 45 °C, which was longer than those of ERL1578 (62.2 min, 59.9–64.6), ERL1576 (33.8 min, 31.6–36.0) and BbHet1 (56.8 min, 54.8–58.9). The exposure
time had a significant effect on the germination rates of the strains (F12,120 = 588.6, P < 0.001). BbHet2 showed the lowest conidial yield, followed by ERL1578, ERL1576 and BbHet1 (F3,72 = 623.8, RGFP966 in vitro P < 0.001), although all colonies showed > 1 × 107 conidia per agar disc at 20 days’ incubation (Fig. 4). BbHet1 produced the greatest number of conidia, 1 × 108 conidia per agar disc. The ERL1576 colony (8.0 × 107 conidia per disc) produced more conidia than the ERL1578 colony (6.9 × 107 conidia per disc) (P < 0.001). There was a significant interaction
between the culture time and the number of conidia per disc (F6,72 = 134.0, P < 0.001). From the observation of radial mycelial growth on ¼SDAY at 10 days, BbHet2 had a faster growth (3.8 ± 0.1 cm diameter) compared with ERL1578 (2.7 ± 0.1 cm), ERL1576 (2.1 ± 0.2 cm) and BbHet1 (1.9 ± 0.2 cm). BbHet2 also had the fastest growth at 3 days (1.4 ± 0.1 cm) and 7 days (2.4 ± 0.1 cm) of observations. Virulence was
measured by the percentage Palbociclib chemical structure of WFT death (mortality). No significant why differences in virulence were observed among the isolated colony treatments (ERL1578, ERL1576, BbHet1 and BbHet2; P > 0.05), but all fungal treatments were more efficacious against WFT compared with the non-treated control (F4,90 = 578.1, P < 0.001) (Fig. 5). At 9 days’ post-treatment, BbHet1 and BbHet2 treatments showed 75.5% and 84.2% mortality, respectively. These mortalities were similar to those of ERL1578 (79.2%) and ERL1576 (74.5%) treatments. Mycelial growth was observed on the surface of WFT in all treatments 9 days post-treatment except the non-treated control. The incubation time had a significant effect on the virulence of the strains (F8,90 = 37.3, P < 0.001). Conidial thermotolerance was positively correlated with the RDV of conidia and negatively correlated with conidial yield, but no relationship between the thermotolerance and their insecticidal activity was found in the PCA at the 0.01 confidence level (Fig. 6). More thermotolerant conidia looked darker under the microscope (Pearson’s correlation coefficient r = 0.969, n = 36, P < 0.001). A linear regression was estimated between the thermotolerance (Y) and the relative densitometric value (X) as follows: Y = 128.4X − 38.9 (R2 = 0.940, = 0.938) (F1,34 = 528.2, P < 0.001).