Reliable Detection for Bean yellow mosaic virus, Canna yellow streak virus, and Canna yellow mottle virus in Canna Varieties with Red Foliage

Cannas grow from rhizomes to produce colorful foliage that ranges from deep burgundy, bronze, green, purple veined, and variegated. Bean yellow mosaic virus (BYMV), Canna yellow streak virus (CaYSV), and Canna yellow mottle virus (CaYMV) are problematic viruses infecting cannas. Their disease characteristics have been reported in green-leaved varieties. This study investigated if rhizome planting stocks can be a source of virus infection. PCR and RT-PCR tests identified BYMV, CaYSV, and CaYMV sequences in 20 canna rhizomes and newly emerging leaves. Immunosorbent electron microscopy tests identified filamentous potyvirus particles in rhizome and leaf tissue. In addition, disease characteristics were examined in a subset of red-leaved varieties 'Australia', 'Burning Ember', and 'Red Futurity' planted in pots in the greenhouse. Plants were assigned identifying codes, visual disease ratings, and samples were taken for RT-PCR and PCR virus detection assays. Statistical analysis was carried out to compare disease ratings with RT-PCR and PCR test results. Visual assessment was found to be not a reliable indicator of virus infection in 'Australia' and 'Burning Ember' plants. 'Red Futurity' produced the most obvious pattern of mosaic disease and virus symptoms were easier to identify in this variety. This study demonstrated that visual assessment was an ineffective method for disease identification for the red-leaved varieties. Growers would be well advised to utilize molecular testing to identify infected plants to aid in the clean-up of the crop.