Assessment of Kweilingia divina as a potential augmentative biological control agent against the gramineous weed Microstegium vimineum

Microstegium vimineum (Trin.) A. Camus, commonly called stiltgrass, is an exotic and indigenous troublesome weed in the United States and eastern Asia, respectively. Between 2020 and 2022, a damaging disease was observed on M. vimineum plants at the foot of Daluo Mountain in Wenzhou City, China, with an incidence of 90 %. Typical rust disease symptoms were prominently visible during the early monsoon season (June to July), consisting of chlorotic spots with many orange or orange-yellow uredinia on the abaxial surfaces of the M. vimineum leaves. Based on morphological and molecular characteristics, the fungus was identified as Kweilingia divina (Syd.) Buriticá. This article describes the studies carried out on one strain of the fungus (WZ-2) to ascertain its potential as a biocontrol agent of the weed. Host specificity testing on 61 plant species from 15 families proved that 25 major crops and 36 weeds were insensitive to this fungus, with only two other gramineous weed species being slightly susceptible. However, urediniospores were not observed on these slightly infected plants. Further research is required to assess the pathogenicity and safety of various plant species to K. divina, especially bamboos, which have been identified as susceptible. Temperature and dew period experiments have shown that the fungus has a relatively wide tolerance for infection between 15 and 40 °C, and with only 4 h of dew exposure some uredinia appeared on artificially infected M. vimineum plants. A field trial proved that urediniospores from the strain WZ-2 could infect naturally occurring M. vimineum plants, causing severe disease symptoms and plant death. Thus, strain WZ-2 has great potential as an augmentative biological control agent against M. vimineum. K. divina is a heteroecious rust fungus that requires an alternate host to complete its life-cycle. What the alternative hosts are, and the impact of the alternate hosts on outbreaks of the disease requires further study.