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Perilla frutescens (L.) Britton, an annual plant in the mint family, is considered invasive in the United States where it excludes native vegetation in natural areas and can cause respiratory illness in livestock. An effective biological control agent would improve perilla management, but none have been developed or proposed. This study investigated the biocontrol potential of a fungal pathogen, Colletotrichum shisoi, recently found infecting perilla in North America. The growth rates and morphology of seven Colletotrichum shisoi isolates were recorded. A virulence assay was performed on two perilla accessions, and the number and size of foliar lesions produced were used to select a single isolate, Colletotrichum shisoi isolate 21-072, exhibiting consistently high virulence for further evaluation of biocontrol efficacy and host specificity. Treatment with 0.5 mL of 1 × 107 spores/mL H2O caused a 52% reduction in shoot height and 84% reduction in root length of invasive perilla seedlings compared to a control treatment (P < 0.001). Seedlings treated with 1 × 108 spores/mL had a 100% mortality rate. Formulation of inoculum in a 1:1 water:oil emulsion reduced dew period requirements for causing >50% plant mortality from 48 to 24 h, but oil emulsions exhibited a mild phytotoxic effect on seedlings. Four additional perilla accessions were susceptible to C. shisoi, and none of 34 other species included in host range experiments developed disease symptoms following inoculation. These results suggest C. shisoi 21-072 could be an effective antagonist of perilla and likely poses a low risk of non-target impacts. [ABSTRACT FROM AUTHOR]

The structure and diversity of wild grass spike-inhabiting Fusarium communities are not well understood. Fifteen common, non-cultivated grasses were surveyed across two years, regions, and land uses for spike-dwelling Fusarium spp. Eleven fungal species were identified from 857 isolates, including two, F. camptoceras and F. lactis, not recorded previously in New York state or on grass hosts. Species diversity and community structure varied by year and region. Land use and host community did not influence Fusarium communities, and no species-specific grass-Fusarium associations were detected. Fusarium communities were divided into two categories, those dominated by F. graminearum and those dominated by F. sporotrichioides. The community formation process is relevant to disease prediction and toxin monitoring in cropping systems as well as to land management practices at the intersection of agricultural and natural spaces. [ABSTRACT FROM AUTHOR]

In addition to causing disease in wheat and other grain crops, Fusarium graminearum is associated with a wide range of forage, weedy and non-cultivated gramineous species.. The nature of these associations is often unclear, and interactions between F. graminearum and these hosts are not well characterized, despite their prevalence in and around cereal fields. We observed differences in the host suitability (competency) of spring wheat and six common grasses during three stages of the pathogen life cycle. Pathogen survival in artificially infested stem tissue was comparable between grasses and wheat over two years with the exception of one host. Sexual and asexual spore production on host stems under laboratory conditions varied significantly but exceeded 1 × 105 spores per dry gram of tissue for all grass species. A seedling root infection assay revealed the apparent resistance of two grasses to root rot and indicated that host preference could vary between pathogen isolates. These findings are relevant for how the role of wild grass hosts in disease epidemics of proximate crops and in pathogen evolution is viewed. Managing weedy grasses in field margins and avoiding gramineous pasture–wheat rotations may reduce local sources of F. graminearum inoculum. Changes in the relative pathogenicity of isolates depending on host species suggest that wild grasses could exert selective pressure on F. graminearum and requires further investigation. [ABSTRACT FROM AUTHOR]

Perilla mint ( Perilla frutescens (L.) Britt.) is an annual plant native to Asia and considered invasive in North America where it has escaped cultivation as an ornamental (Miller 1947; Swearingen et al. 2010). In August 2021, an anthracnose disease was observed on invasive perilla found along the disturbed margins of a forest in Frederick County, Maryland, United States. Symptoms included necrotic lesions with chlorotic halos, were concentrated in the lower canopy, and caused premature defoliation of lower leaves (Figure S1). Leaves from four plants were surface sterilized by rinsing for 30 s in 70% ethanol, 60 s in 0.8% NaClO, and 60 s in sterile water and then incubated on 2% water agar under ambient laboratory conditions to permit sporulation. After three days, spores that exuded from individual lesions were streaked onto acidified potato dextrose agar. Two single-conidium isolates were recovered from each plant. All eight isolates were identified to species using DNA sequences. A single isolate (21-067) was selected at random for morphological characterization and completion of Koch's postulates. Morphological features were recorded after seven days of growth on synthetic low-nutrient agar (SNA) and potato dextrose agar (PDA) incubated at 22°C under 12 hr UV-B and white fluorescent lighting. Measurements were based on a minimum of 20 observations per structure. Cultures on SNA were flat, hyaline to pale salmon, lacked sporodochia and grew at a rate of 1.3 mm day -1 (n = 3). Vegetative hyphal width was (minimum-maximum) 1.5-4.0 μm, (average ± standard deviation) 2.7 ± 0.9 μm. Conidiophores arose directly from hyphae, were hyaline, smooth, unbranched and measured 40.0-180.0 x 1.5-4.5 μm, 102.3 ± 33.9 x 2.7 ± 0.8 μm. Conidia were single celled, straight, hyaline, glabrous, rounded at both ends and measured 10.0-20.0 x 3.8-6.3 μm, 15.4 ± 2.5 x 4.9 ± 0.7 μm. Setae, observed only on PDA, were pale brown, 1-2 septate, straight, blunt tipped and measured 42.5-97.5 μm, 70.8 ± 13.4 μm. Appressoria formed on PDA were single-celled, pigmented, smooth, and obovoid with entire margins, measuring 5.2-7.7 x 8.6-13.8 μm, 6.8 ± 0.6 x 10.8 ± 1.4 μm. These characteristics were consistent with members of the Colletotrichum destructivum species complex. Partial DNA sequences from five loci were amplified following the procedures of Damm et al. 2014: internal transcribed spacer region of rDNA (ITS), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), chitin synthase 1 (CHS-1), actin (ACT), and beta-tubulin (TUB2). Pairwise sequence comparisons to references using the Blastn algorithm found 99.8% similarity between isolate 21-067 and ex-type C. shisoi isolate JCM 31818: MH660930 (ITS, 545/546 bp), MH660931 (GAPDH,192/192 bp), MH660929 (CHS-1, 278/280 bp), MH660928 (ACT, 262/262 bp), and MH660932 (TUB2, 511/511 bp) (Altschul et al. 1990; Gan et al. 2019). Subsequently, sequences from all eight isolates were aligned with Clustal Omega (Sievers and Higgins 2018), concatenated, and used in a Bayesian phylogenetic reconstruction (Huelsenbeck and Ronquist 2001) of the C. destructivum species complex (Figure S2), confirming the species identity as C. shisoi . Sequences were deposited in NCBI GenBank under accession numbers OM865277-OM865284 and OM885059-OM885090. Koch's postulates were fulfilled using perilla grown in a greenhouse until second true leaves emerged. Inoculum washed from two-week-old fungal cultures grown on potato dextrose agar was adjusted to 4 x 10 4 conidia mL -1 and applied to three replicate plants with an aspirator until runoff. Three plants were sprayed with sterile water as a negative control. Plants were covered with plastic bags for 72 hrs and maintained in a growth chamber at 20°C and 80% RH for 14 days. Inoculated plants displayed disease symptoms similar to those observed under field conditions, and control plants did not develop symptoms. Colletotrichum shisoi was reisolated from symptomatic tissue and reidentified based on morphology. The experiment was completed twice. To the authors' knowledge, this is the first report of C. shisoi on P. frutescens in the United States. Colletotrichum shisoi has not been reported as a pathogen on other plants in the United States and may have potential use as a biological control agent for invasive perilla.