Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2005
Publication Date: 8/1/2005
Citation: Lartey, R.T., Caesar, T., Caesar, A.J., Shelver, W.L., Sol, N.I., Bergman, J.W. 2005. Safflower: A new host of cercospora beticola. Plant Disease. 89(8):797-801. Interpretive Summary: Two different species of the fungus Cercospora have been documented to infect and cause diseases in safflower and sugar beet. Cercospora carthami is known to infect safflower while Cercospora beticola causes Cercospora leaf spot, one of the most important leaf diseases of sugar beet. Safflower is an oilseed crop adapted to the small-grain production areas of the western Great Plains including the Northern Plains Area (NPA) where it is being assessed for potential rotation with sugar beet. Like most places where sugar beet is grown, Cercospora leaf spot disease is quite common in the NPA but incidence of C. carthami has not been observed on safflower. Occurrence of unusual spots on leaves of irrigated safflower at Sidney, Montana in the NPA prompted this study of safflower as a possible host of C. beticola. Safflower plants were infected with four isolates of C. beticola (C1, C2, Sid1 and Sid2) and maintained in growth chambers. Between 3 and 4 weeks, leaf spot symptoms appeared on the infected leaves. Using a recently developed PCR technique, we detected C. beticola in the lesion tissues of the diseased leaves. Single spores were isolated from the leaf lesions, cultured on agar and colonies were subjected to the PCR. Our PCR results confirmed that the cultures were from C. beticola. As an additional proof, an antibody that was raised from C. beticola isolate C2 also bound to antigens from the single spore cultures of all four C. beticola isolates. Inoculum from single spore cultures which were isolated from infected safflower was then used to infect sugar beet plants. The infected plants developed typical Cercospora leaf spot of sugar beet symptoms. Using the PCR technique, we were able to detect C. beticola in the sugar beet leaf lesions. The pathogen C. beticola was never detected in uninfected safflower or sugar beet by either the PCR technique or with the antibody. Our results demonstrate that safflower is a new host of C. beticola.
Technical Abstract: Safflower is an oilseed crop adapted to the small-grain production areas of the western Great Plains including the Northern Plains Area (NPA). In the NPA, safflower production is being evaluated for potential rotation with sugar beet. Safflower is susceptible to Cercospora carthami while sugar beet is susceptible to Cercospora beticola. C. carthami has not been observed on safflower in the NPA but C. beticola is ubiquitous on sugar beet. Observation of unusual leaf spots on irrigated safflower cv. Centennial at Sidney, MT prompted this investigation of safflower as a potential alternate host of C. beticola. Safflower plants were inoculated with four isolates of C. beticola (C1, C2, Sid1 and Sid2) and incubated in growth chambers; leaf spot symptoms appeared between 3 and 4 weeks later. PCR amplification of extracts from lesion leaf tissue with C. beticola-specific primers produced fragments comparable to amplified fragments from purified cultures of control C. beticola. PCR assay of cultures of single spores from diseased safflower leaf lesions also produced fragments comparable to fragments from C. beticola cultures. Antibody that was raised from isolate C2 also bound to antigens from the single spore cultures of the four C. beticola isolates. Inoculum from single spores cultures from infected safflower also infected sugar beet and produced typical Cercospora leaf spot symptoms. Assay of these leaf lesions by PCR, resulted in amplification of target fragments with the C. beticola specific primers. Our results demonstrate that safflower is a new host of C. beticola.