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

Abstract

Rust (Melampsora apocyni) on Apocynum venetum is the major constraint to the commercial development of this medicinal herb. To determine the factors influencing rust intensity (maximum disease index [DI max ]), rust was investigated from 2011 to 2015 in both cultivated and wild A. venetum plants. Partial least squares path modeling (PLS-PM) was used to analyze the paths and extent of the factors related to pathogen, environment, and host that affect rust intensity. DI max exhibited considerable variations across years and study sites, with variations linked to various factors fostering disease development. PLS-PM explained 80.0 and 70.1% of variations in DI max in cultivated and wild plants, respectively. Precipitation was the key factor determining DI max in both cultivated and wild plants (path coefficient [PC] = 0.313 and 0.544, respectively). In addition, the topsoil water content in cultivated plants and the total vegetation coverage in wild plants were also critical determinants of DI max via their effects on the microclimatic factor (contribution coefficients [CC] = 0.681 and 0.989, respectively; PC = 0.831 and 0.231, respectively). In both cultivated and wild plants, host factors were mainly dominated by A. venetum density (CC = 0.989 and 0.894, respectively), and their effect on DI max via the microclimatic factor (PC = 0.841 and 0.862, respectively) exceeded that via the inoculum factor (PC = 0.705 and 0.130, respectively). However, the indirect effects led to DI max variation, while the dilution effect on host (CC = 0.154) from weed in wild plants led to the indirect effect size in wild plants of 0.200, which was lower than _ 0.699 in cultivated plants.

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

“…The absence of the symptomatic leaves in the field could be linked to Luobuma rust disease caused by Melampsora apocyni , an aggressive causal agent in the field, with an incidence rate of up to 90% and whose urediospores could cover the whole leaves in severe cases 21 . The rust disease of Luobuma usually occurs from late June to early July in Yuzhong; however, the stem necrotic lesions disease of Luobuma began in late July to early August.…”

Leaf Spot Disease of Red Clover Caused by Leptosphaeria weimeri (=Longiseptatispora meliloti) in China

“…Within each plot, 50 leaves of red clover were randomly chosen for each point to assess both the incidence and severity of the disease. Subsequently, the incidence rate (I) and disease index (DI) were computed utilizing the following formulas [23]:…”

Luobuma Leaf Spot Disease Caused by Alternaria tenuissima in China

“…The investigations were carried out on 29 September 2018, and 23 June and 23 September 2019. The disease surveillance was conducted based on a method used to investigate A. venetum rust [20]. The severity of leaf spot disease was visually estimated as the percentage of leaves covered with black scab and the results were expressed on a scale of 0-5 as follows: 0 for no signs of infection; 1 for 0.1% to 5% leaf area covered with black scab; 2 for 5.1% to 20%; 3 for 20.1% to 50%; 4 for 50.1% to 75%; and 5 for >75.1%.…”