Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 24, 2009
Publication Date: November 1, 2009
Citation: Jones, R.W., Stommel, J.R., Wanner, L.A. 2009. First report of Oidiopsis taurica causing powdery mildew outbreak on pepper in Maryland. Plant Disease. 93:1222.
Interpretive Summary: While there are many diseases that affect plants, they may be present only in certain parts of the world. When a disease appears in a new location, scientists document the occurrence so others can become aware of the potential for the disease in a new location. We identified the first occurrence of a foliar disease called powdery mildew on pepper plants. Reports of a new disease aid in determining how the disease causing organism appeared at the new location. This information is used by growers to aid in controlling plant disease.
Pepper plants grown in large experimental plots at Beltsville Maryland showed widespread powdery mildew infection in the late summer of 2008. Extensive coverage of the abaxial surface by white patches of conidia was noted, along with chlorotic regions on the adaxial surface. Samples were taken for DNA extraction and subsequent PCR amplification of the ITS regions (1). The amplified band was cloned and sequenced, verifying the pathogen as Oidiopsis taurica (teleomorph Leveillula taurica). Multiple chili pepper and bell pepper plants were inoculated with conidia from an infected bell pepper plant by placement in a spore deposition chamber. Signs of powdery mildew were evident three weeks after spore deposition. DNA samples were again analyzed and verified as O. taurica (deposited as GenBank #GQ167201).
Powdery mildew infection was observed in a diversity of pepper accessions that included Capsicum annuum, C. baccatum, C. chinense and C. frutescens. The C. annuum accessions included culinary bell pepper cultivars and breeding lines as well as a diverse collection of ornamental breeding lines, heirlooms and land races. Infection was widespread in field plots and host resistance within any single species or ideotypes was not evident. Disease occurred with equal severity in plants with open or compact and upright or prostrate growth habits, again suggesting a new, more aggressive isolate than that found in other studies (2). The unexpected occurrence of powdery mildew on pepper in Maryland allowed widespread infection to occur prior to recognition of the emergent disease. Significant leaf damage was incurred leading to partial defoliation where infection was most severe. Application of Quadris (azoxystrobin) was effective in limiting further crop damage. Subsequent powdery mildew infection was identified on pepper under greenhouse conditions during the winter of 2008. Application of Strike (triadimefon) provided effective control in the greenhouse.
This disease is new to the mid-Atlantic region of the U.S. It has been reported in greenhouse peppers growing in Ontario, Canada, where it has become a recurring problem requiring fungicide intervention (3). The isolate we are reporting may be more virulent on pepper, as nearby tomatoes did not show evidence of infection.
No cleistothecia were found on infected leaves. Given the wide host range of O. taurica and the systemic nature of infections, it is likely that the fungus has become established in Maryland on perennial host plants.