Factors Influencing Rust (Melampsora apocyni) Intensity on Cultivated and Wild Apocynum venetum in Altay Prefecture, China

Characterization of rhizospheric fungi and their in vitro antagonistic potential against myco-phytopathogens invading Macrotyloma uniflorum plants

Microorganisms have become more resistant to pesticides, which increases their ability to invade and infect crops resulting in decreased crop productivity. The rhizosphere plays a crucial role in protecting plants from harmful invaders. The purpose of the study was to investigate the antagonistic efficiency of indigenous rhizospheric fungal isolates against phytopathogens of M. uniflorum plants so that they could be further used as potent Biocontrol agents. Thirty rhizospheric fungal isolates were collected from the roots of the Macrotyloma uniflorum plant and initially described morphologically for the present study. Further, in vitro tests were conducted to evaluate the antifungal activity of these strains against four myco-phytopathogens namely Macrophamina phaseolina, Phomopsis sp. PhSFX-1, Nigrospora oryzae, and Boeremia exigua. These pathogens are known to infect the same crop plant, M. uniflorum, and cause declines in crop productivity. Fifteen fungal strains out of the thirty fungal isolates showed some partial antagonistic activity against the myco-phytopathogens. The potent fungal isolates were further identified using molecular techniques, specifically based on the internal transcribed spacer (ITS) region sequencing. Penicillium mallochii, Cladosporium pseudocladosporioides, Aspergillus chevalieri, Epicoccum nigrum, Metarhizium anisopliae, and Mucor irregularis were among the strains that were identified. These potent fungal strains showed effective antagonistic activity against harmful phytopathogens. Current findings suggest that these strains may be taken into consideration as synthetic fungicides which are frequently employed to manage plant diseases alternatives.

Luobuma Leaf Spot Disease Caused by Alternaria tenuissima in China

Luobuma (Apocynum venetum and Poacynum hendersonni) is widely cultivated for environmental conservation, medicinal purposes and the textile industry. In 2018, a severe leaf spot disease that attacked the leaves of Luobuma was observed in plants cultivated in Yuzhong County, Gansu Province, China. Symptoms of the disease appeared as white or off-white spots surrounded by brown margins on the leaves of A. venetum. The spots expanded and covered a large area of the leaf, presenting as "cankers" with progression of the disease, leading to leaf death. The initial symptoms of the disease on P. hendersonni were similar to the symptoms of A. venetum, with a larger disease spot than A. venetum, and the spot was black and thicker. The aim of this study was to identify the fungal species and evaluate the effectiveness of fungicides (hymexazol and zhongshengmycin) against the pathogen in vitro. The fungi species that caused the new disease was identified as Alternaria tenuissima based on the morphological characteristics, pathogenicity tests, and phylogenetic analysis of the internal transcribed spacer (ITS) region, glyceraldehyde 3-phosphate dehydrogenase (gpd), translation elongation factor 1-alpha (TEF) and the histone 3 (H3) gene sequences. The findings showed that hymexazol fungicide can be used to control leaf spot disease. This is the first report on Luobuma leaf spot disease caused by A. tenuissima in China.

Characterization of Boeremia exigua causing stem necrotic lesions on Luobuma in northwest China

Luobuma (Apocynum venetum, Poacynum pictum, and P. hendersonni) are perennial herbs widely used in the textile and medical industries and ecological restoration. In the summer of 2020, reddish-brown or off-white sunken shape necrotic lesions were observed on the stems and shoots of seven Luobuma ecotypes grown in the field in Yuzhong County, Gansu province of China, which is a limiting factor that affects the growth, function and application of Luobuma. To make clear whether the new symptoms were caused by a novel pathogen, a combined research in field and greenhouse was conducted. Based on the morphological and molecular analysis results, the pathogen causing the necrotic lesions was identified as Boeremia exigua var. rhapontica. The incidence and disease index of the seven ecotypes in the field ranged from 11.49 to 33.68% and 6.63 to 23.01, respectively, from 2020 to 2021. The results showed that the disease severity gradually increased with the growing season. According to the pathogenicity analysis of the eight ecotypes in the greenhouse, the ecotypes Pp-BMK and Pp-BMH were susceptible, while ecotype Pp-BMQ was resistant to Boeremia exigua var. rhapontica infection. Thus, the present study provides a theoretical basis for preventing and controlling the stem and leaf necrotic lesions disease on Luobuma by planting resistant varieties/ecotypes. To our knowledge, this is the first report of stem necrotic lesions and leaf spots on Luobuma caused by B. exigua var. rhapontica.