The occurrence of rust disease, and biochemical and physiological responses on Apocynum venetum plants grown at four soil water contents, following inoculation with Melampsora apocyni

Abstract

We studied the development of rust disease, and biochemical and physiological responses, on Apocynum venetum plants inoculation with Melampsora apocyni that were growing in a greenhouse at four relative soil water contents. The soil conditions were 25% (severe drought), 50% (mild drought), 75% (optimal) and 100% (waterlogging) relative soil water content. Plants exposed to drought and waterlogging stress had a lower number of open stomata before inoculation, corresponding with the disease index on the 10th day after inoculation being lower than that of the optimal soil water condition. Inoculated plants exposed to severe and mild drought stress had a gradually enhanced resistance to the rust disease from the 10th day after inoculation, corresponding with the enhanced activity of polyphenol oxidase and phenylalanine ammonialyase. For the inoculated plants exposed to severe drought stress, hydrogen peroxide always remained at the highest level for any treatment, and they had a rapidly enhanced activity of peroxidase, two factors that were associated with suppression of disease development. A. venetum plants exposed to double stress of waterlogging and disease had a high activity of peroxidase that not only removed reactive oxygen to prevent or reduce cell injury but also enhanced resistance to the rust disease. In addition, a rapidly enhanced activity of phenylalanine ammonialyase in the waterlogging condition from the 25th day after inoculation was also associated with an enhanced resistance to the rust disease. Drought and waterlogging stress had a negative effect on the leaf photosystem, and in particular, there was a significant decrease in the net photosynthetic rate with an increase in the duration and degree of drought stress, and this lead to a statistically significant decrease in the weight of aboveground tissue compared with that of plants under optimal soil water condition (P 0.05) decrease in the weight of aboveground tissue compared with that of non-inoculated plants under drought stress.