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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 rubber tree seedlings with leaves at three phenological stages (copper bronze, colour‐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 =.296) whilst temperature did (p <.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 <.0001). At 10 and 35°C, more than 2 and 4 days were needed for infection to complete, respectively, compared to <2, 1, 0.5, and 0.5 days for 15, 20, 25, and 35°C, respectively. 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 only at 15°C. The latent period on the copper bronze leaves at 15°C 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 affected germination and postgermination growth of rubber tree powdery mildew, whereas leaf age primarily affected postgermination growth of the pathogen. [ABSTRACT FROM AUTHOR]

In this study, a real-time PCR assay was established to quantify airborne inoculum of Blumeria graminis f. s p. tritici ( Bgt), the causal agent of wheat powdery mildew. Burkard 7-day recording spore traps were used to collect Bgt spores in air in Langfang City, Hebei Province, China. A linear relationship between number of spores counted with a compound microscope and those determined with the real-time PCR assay was obtained in artificially inoculated spore trap tape sections. The dynamics of airborne conidia concentrations of Bgt were similar. There were significant correlations ( P < 0.01) between spore concentrations by using a compound microscope and the real-time PCR assay in three growing seasons. The results demonstrated a potential method to quantitatively determine spore inoculum potential in wheat fields by using a real-time PCR assay. [ABSTRACT FROM AUTHOR]

In order to manage agricultural pathogens, it is crucial to understand the population structure underlying epidemics. Rubber tree powdery mildew, caused by Erysiphe quercicola , is a serious threat to rubber plantations worldwide, especially in subtropical environments including all rubber tree-growing regions in China. However, the population structure of the pathogen is uncertain. In this study, 16 polymorphic microsatellite markers were used to genotype powdery mildew samples from the main rubber tree-growing regions including Yunnan (YN), Hainan (HN), western Guangdong (WG), and eastern Guangdong (EG). YN had higher genotypic diversity (Simpson's indices), genotypic evenness, Nei's gene diversity, allelic richness, and private allelic richness than the other regions. Cluster analysis, discriminant analysis of principal components, pairwise divergence, and shared multilocus genotype analyses all showed that YN differed significantly from the other regions. The genetic differentiation was small among the other three regions (HN, WG, and EG). Analysis of molecular variance indicated that the variability among regions accounted for 22.37% of the total variability. Genetic differentiation was significantly positively correlated ( R xy = 0.772, P = 0.001) with geographic distance. Linkage equilibrium analysis suggested possible occurrence of sexual recombination although asexual reproduction predominates in E. quercicola . The results suggested that although significant genetic differentiation of E. quercicola occurred between YN and the other regions, pathogen populations from the other three regions lacked genetic differentiation., Competing Interests: The author(s) declare no conflict of interest.