Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2012
Publication Date: N/A
Citation: Interpretive Summary: Camelina is a potential biofuel and oilseed crop that is adapted to the dryland areas of the Pacific Northwest. We describe the identification of a new disease on this crop in Washington state- downy mildew caused by Hyaloperonospora camelinae. We showed that the disease is seed transmitted, and can be reduced by seed treatment with mefanoxam, an Oomycete specific fungicide.
Technical Abstract: Camelina (Camelina sativa [L.] Crantz) plants with symptoms of downy mildew were obtained from three different locations in Washington State. Based on PCR and sequencing of the ITS1-5.8S-ITS2 region, the causal pathogen was identified as Hyaloperonospora camelinae. The PCR primers consistently amplified 699 bp bands from the infected plants, but not from the asymptomatic plants. A comparison of the sequences with those in GenBank revealed 100% sequence similarity to H. camelinae. Growth and development of the H. camelinae was observed in different tissues using light and scanning electron microscopy (SEM). Light microscopic observation revealed the presence of oospores in the infected leaves and SEM revealed the presence of conidia and conidiophores on the seed surface. To determine whether H. camelinae is a seed-transmitted pathogen, seeds collected from infected plants were planted in Sunshine professional growing mix maintained in a growth chamber. Disease symptoms were observed in 96% of the seedlings compared to 3% of the seedlings grown from seed from asymptomatic plants, which indicates that H. camelinae is a seed-transmitted pathogen. Seeds treated with mefenoxam, a fungicide specific for Oomycetes, significantly reduced the incidence of the disease.