The discovery of natural bioactive compounds from endophytes or medicinal plants against plant diseases is an attractive option for reducing the use of chemical fungicides. In this study, three compounds, indole-3-carbaldehyde, indole-3-carboxylic acid (3-ICA), and jasmonic acid (JA), were isolated from the EtOAc extract of the culture filtrate of the endophytic fungus Lasiodiplodia pseudotheobromae LPS-1, which was previously isolated from the medicinal plant, Ilex cornuta. Some experiments were conducted to further determine the antifungal activity of these compounds on wheat powdery mildew. The results showed that JA was much more bioactive than indole-3-carbaldehyde and 3-ICA against Blumeria graminis, and the disease severity caused by B. graminis decreased significantly with the concentration increase of JA treatment. The assay of the interaction of 3-ICA and JA indicated that there was a significant synergistic effect between the two compounds on B. graminis in each of the ratios of 3-ICA to JA (3-ICA:JA) ranging from 1:9 to 9:1. When the compound ratio of 3-ICA to JA was 2:8, the synergistic coefficient was the highest as 22.95. Meanwhile, a histological investigation indicated that, under the treatment of JA at 500 μg/ml or 3-ICA:JA (2:8) at 40 μg/ml, the appressorium development and haustorium formation of B. graminis were significantly inhibited. Taken together, we concluded that JA plays an important role in the infection process of B. graminis and that 3-ICA as a synergist of JA enhances the antagonism against wheat powdery mildew.

Wheat root rot disease due to soil-borne fungal pathogens leads to tremendous yield losses worth billions of dollars worldwide every year. It is very important to study the relationship between rhizosphere soil fungal diversity and wheat roots to understand the occurrence and development of wheat root rot disease. A significant difference in fungal diversity was observed in the rhizosphere soil of healthy and diseased wheat roots in the heading stage, but the trend was the opposite in the filling stage. The abundance of most genera with high richness decreased significantly from the heading to the filling stage in the diseased groups; the richness of approximately one-third of all genera remained unchanged, and only a few low-richness genera, such as Fusarium and Ceratobasidium, had a very significant increase from the heading to the filling stage. In the healthy groups, the abundance of most genera increased significantly from the heading to filling stage; the abundance of some genera did not change markedly, or the abundance of very few genera increased significantly. Physical and chemical soil indicators showed that low soil pH and density, increases in ammonium nitrogen, nitrate nitrogen and total nitrogen contributed to the occurrence of wheat root rot disease. Our results revealed that in the early stages of disease, highly diverse rhizosphere soil fungi and a complex community structure can easily cause wheat root rot disease. The existence of pathogenic fungi is a necessary condition for wheat root rot disease, but the richness of pathogenic fungi is not necessarily important. The increases in ammonium nitrogen, nitrate nitrogen and total nitrogen contributed to the occurrence of wheat root rot disease. Low soil pH and soil density are beneficial to the occurrence of wheat root rot disease.

Pseudomonas syringae pv. actinidiae (Psa) is the causal agent of kiwifruit canker, a serious threat to commercial kiwifruit production worldwide. Studies of the movement path and the survival time of Psa in the host are crucial for integrated management programs. Hence, we used Psa with GFPuv gene (Psa-GFPuv) strain to investigate the movement path of Psa in leaves and branches, and the survival time of Psa in leaves under different environmental conditions. We found that the pathogen Psa spread longitudinally in the branches and leaves rather than transverse path. Additionally, the survival time of bacteria in fallen leaves under different environmental conditions were simulated by the way of Psa infecting the detached kiwifruit leaves. Psa survives the longest, up to 43 days in detached kiwifruit leaves with high humidity (above 80%) at 5 °C, and up to 32 days with low humidity (20%). At 15 °C, the Psa can survive in detached kiwifruit leaves for 20–30 days with increasing humidity. At 25 °C, it can only survive for 3 days with low humidity (20%) and 15 days with high humidity (above 80%). Furthermore, the population growth experiments showed that bacterial growth of Psa was more favorable in detached kiwifruit leaves with above 80% humidity at 5 °C. These results suggest that the survival condition of Psa in detached kiwifruit leaves is significantly affected by environmental conditions, and provide the basis for the control timing and technology of kiwifruit canker.