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Powdery mildew is an important
disease of rubber trees worldwide.
To assess the effects of temperature and leaf age on conidial germination and
disease development, conidia were inoculated onto leaves of rubber tree
seedlings at three phenological stages (copper
bronze, color changing and light green) and then incubated at six
constant temperatures (10, 15, 20, 25, 30 and 35 °C). Leaf age did not affect conidial
germination (P = 0.296) while
temperature significantly affected conidial germination (P < 0.0001) although conidia were able to germinate at all
tested temperatures. The estimated optimal temperature for conidial germination
was 23.2 °C. Leaf age, temperature and their interactions had significant
effects on conidial infection and hypha number (P < 0.0001). At 10 and 35°C, more time (2-5 days) was needed for
infection to complete, compared to < 2 days for other combinations.
Sporulation and mildew symptoms were only observed on those inoculated leaves
of all stages at 20 and 25 °C, and at the copper
bronze stage at 15 °C only. At 15°C, the latent period on the copper
bronze leaves was longer (9 days) than at 20 and 25 °C (4 days). The latent
period at 20 and 25°C increased from 4 to 7 days as the leaf development stage
increased from copper bronze to light green. Therefore, temperature affects germination and post-germination growth of rubber
tree powdery mildew, whereas leaf age primarily affects post-germination growth
of the pathogen.