Pathogenicity of conidia-based preparations of entomopathogenic fungi against the greenhouse pest aphids Myzus persicae, Aphis gossypii, and Aulacorthum solani (Hemiptera: Aphididae).

Seeking new isolates of entomopathogenic fungi with greater virulence against greenhouse aphid pests than those currently registered in North America for control of these insects, single-dose screening assays of 44 selected fungal isolates and 4 commercially available strains were conducted against first-instar nymphs of Myzus persicae and Aphis gossypii. The assays identified a number of Beauveria and Metarhizium isolates with virulence equal to or greater than that of the commercial strains against the nymphal aphids, but none exhibited exceptionally high virulence. Virulence of Isaria isolates was unexpectedly low (<31% mortality at doses>1000conidia/mm(2)). In dose-response assays, Beauveria ARSEF 5493 proved most virulent against M. persicae and A. gossypii; however, LC50s of this isolate did not differ significantly from those of B. bassiana commercial strain JW-1. Dose-response assays were also conducted with Aulacorthum solani, the first reported evaluations of Beauveria and Metarhizium against this pest. The novel isolate Metarhizium 5471 showed virulence⩾that of Beauveria 5493 in terms of LC25 and LC50, but 5493 produced a steeper dose response (slope). Additional tests showed that adult aphids are more susceptible than nymphs to fungal infection but confirmed that infection has a limited pre-mortem effect on aphid reproduction. Effects of assay techniques and the potential of fungal pathogens as aphid-control agents are discussed.

First Report of Downy Mildew Caused by Peronospora belbahrii on Basil (Ocimum spp.) in Ontario.

Basil (Ocimum spp.) is one of the most commercially significant fresh culinary herb crops worldwide. In Ontario, basil is grown both in the field and in the greenhouse. In the summer of 2011, basil plants grown in a research field at the Simcoe Research Station in Norfolk County, Ontario, Canada (44°15'N, 77°35'W), were infected with downy mildew. Infected leaves exhibited interveinal chlorotic lesions on the upper surface and clear to black sporulation on the abaxial leaf surfaces. Leaf senescence and defoliation occurred at high disease severity, which reduced marketable yield. Basil downy mildew symptoms were severe on leaves of cultivars Genovese and Sweet Basil, with 40 to 100% disease incidence. Based on morphological characteristics, the basil downy mildew causal agent was identified as Peronospora belbahrii Thines (4). Infected leaves were collected and microscopic observations of the sporulating lesions were carried out and the structures measured. Sporangiophores (n = 20) were hyaline with relatively long, straight trunks and were monopodially branched, with a length of 150 to 360 µm (average 285 µm). Sporangiophores ended with two slightly curved branchlets, the longer one measuring 15 to 27 µm (average 19 µm) and the shorter one 5 to 15 µm (average 9 µm). Sporangia (n = 50) were round, or slightly ovoid, olive to brown in color, and measured 29 × 25 µm (25 to 35 × 20 to 30 µm). Genomic DNA was extracted from 10 isolates and the nuclear ribosomal internal transcribed spacer (ITS) region was amplified with ITS4 and ITS5 primers and sequenced. The sequences of the 10 isolates were nearly identical. A BLAST search of the NCBI database with the ITS sequences (GenBank Accession No. KC756923) revealed a 98 to 100% similarity to the sequences of P. belbahrii (HQ730979, FJ436024, and HQ702191) isolated from sweet basil in Florida (3), California (1), and Hungary (2), respectively. To confirm pathogenicity, 5-week-old 'Genovese' seedlings were sprayed with a suspension of 1 × 105 sporangia/ml. Plants were kept in a growth chamber maintained at 23/18°C, 60 to 85% relative humidity, and 12/12 h light/dark. Non-inoculated plants served as controls. Basil downy mildew symptoms developed after 8 days on the inoculated plants and the pathogen was identified in association with symptoms consistent with downy mildew. The non-inoculated controls remained healthy. In North America, the occurrence of basil downy mildew has been reported since 2007 (3) and the disease has spread into several U.S. states. To our knowledge, this is the first report of downy mildew on sweet basil in Canada. References: (1) C. L. Blomquist et al. Plant Dis. 93:968, 2009. (2) G. Nagy and A. Horvath. Plant Dis. 95:1034, 2011. (3) P. D. Roberts et al. Plant Dis. 98:199, 2009. (4) M. Thines et al. Mycol. Res. 113:532, 2009.