The influences of biotic and abiotic factors on the occurrence and severity of poplar canker disease in Qingfeng County, China and the management implications

Landscape pathology is a research approach that can provide validation of the effectiveness of regional controls of forest disease at a landscape scale. In this paper, we analyzed the effects of stand features, management approaches, and geographical locations on poplar canker disease incidence （DI） and disease severity index （DSI） of individual trees at a 10 km x 10 km mesoscale landscape in Qingfeng County, China. DI varied significantly with stand age, tree densities, and the degree of canopy closure. DI in stands younger than 4 years old was significantly lower than that in the stands over 6 years old and reached the highest value at a stand age of 8-10 years. Overall, DI was positively correlated with stand age, stand density, andthe degree of canopy closure. DI was significantly lower in agro-forest stand patches than in other three patch types, i.e. isolated patch, pure stand patch, and mixed stand patch. Poplar plantations distributed around and near to villages exhibited significantly higher DI mainly due to human activities and herbivores. Fragmentation or connectivity in this mesoscale landscape seemed not impact disease occurrence. DSI was not significantly correlated with stand density, but varied significantly with tree varieties and trees ages. DSI was highest in stands of 10-12 year trees for all poplar varieties we studied here. Plantation density and plantation age were thus critical factors in determining DI and DSI. A logistic predictive model of disease occurrence was developed for the study area, considering varieties, age, height, density, canopy cover, stand types, patch types, management status, and stand geographical locations. Our study here shows that adjustment of stand density by thinning at different plantation ages is an effective approach controlling the occurrence canker disease in short-rotation poplar plantations at the landscape scale.

Transcriptomic and Physiological Analyses of Pigment Accumulation in Eucommia ulmoides‘Hongye’

Eucommia ulmoides‘Hongye’is a new ornamental variety of E.ulmoides with excellent red or purple foliage.We found that E.ulmoides‘Hongye’exhibited a gradual change from green to red colour under light conditions.However,the colouring mechanism in the leaves of E.ulmoides‘Hongye’remains unclear.In this study,we compared the pigment content and leaf colour index of E.ulmoides‘Hongye’at five stages with those of E.ulmoides‘Xiaoye’,which was used as the control variety.The transcriptome sequencing data of the first-period(H1,green)and fifth-period(H5,red)leaves were also analysed and compared.The corresponding gene regulation in anthocyanin-related metabolic pathways was then analysed.Physiological results indicated that the contents of flavonoids and anthocyanins in red leaves(H5)were significantly higher than those in green leaves(H1),whereas the chlorophyll content in red leaves(H5)was lower than that in green leaves(H1).Moreover,the carotenoid content did not significantly differ between the two varieties.A transcriptome analysis identified 4240 differentially expressed genes(DEGs),and 20 of these genes were found to be involved in flavonoid and anthocyanin biosynthesis pathways.The results provide a reference for further study of the leaf colouration mechanism in E.ulmoides.