An estimated 200 hectares of basil varieties are grown annually for fresh and wholesale markets in New Jersey. In July of 2018, leaf spot disease symptoms were observed on several sweet basil cultivars and breeding lines grown in university field trials at the Rutgers Agricultural Research and Extension Center near Bridgeton, New Jersey. Disease incidence was less than 10% and no differences in susceptibility were observed between varieties or breeding lines of sweet basil within the field. Symptoms were observed as irregularly shaped blackened necrotic spots on leaf margins ranging from 2mm to 7mm in diameter, which coalesced as lesions expanded over time.
The scientists of Rutgers University have isolated the pathogen from leaves with symptoms, then they have identified the isolates by the gene sequences and determined the pathogenicity. Molecular analyses and pathogenicity test have confirmed Pseudomonas cichorii as causal agent. Similar symptoms on basil have been observed by New Jersey growers in previous years, the cause was never confirmed. To our knowledge, this is the first report of bacterial leaf spot caused by P. cichorii on Ocimum basilicum in the state. Since bacterial leaf spot caused by P. chicorii poses a significant threat to sweet basil production in the US, further research on selecting and breeding natural sources of resistance and chemical control are needed.
The image used comes from Growing Small Farms
Source: Nrupali Patel, Donald Y. Kobayashi, Anthony J. Noto, Amie C Baldwin, James E. Simon, Andrew Wyenandt, 'First Report of Pseudomonas cichorii causing Bacterial Leaf Spot on Sweet Basil (Ocimum basilicum) in New Jersey', online on 3 June 2019, Plant Disease.