Pseudomonas cannabina

Pseudomonas cannabina was once classified as Pseudomonas syringae pv. cannabina, but after extensive DNA testing of several P. syringae pathovars, P. cannabina was declared its own species, known as genomospecies 9.[2] P. cannabina turns out to have at least two pathovars of its own: P. cannabina pv. cannabina and P. cannabina pv. alisalensis (formerly known as P. syringae pv. alisalensis).[3] This distinction is supported by a difference in host range between the pathovars as well as physiological differences including carbon source utilization, bacteriophage sensitivity, and pigment production.[4] P. cannabina pv. cannabina has only been shown to be pathogenic on Cannabis sativa, while P. cannabina pv. alisalensis has been shown to be pathogenic on broccoli, broccoli raab, radish, arugula, and oat, and probably infects other crucifers and grains though identification is difficult given the genomic confusion in the literature.[3][4] For example, P. cannabina pv. alisalensis has also been shown through Multi-Locus Sequence Analysis to be responsible for bacterial blights in crucifers formerly associated with the B70 strain of Pseudomonas syringae maculicola identified on radish in Wisconsin in 1965.[4]

In crucifers, P. cannabis pv. alisalensis causes a blight on the leaves (appearing similarly to those caused by P. syringae as well as the common fungal disease Brown Leaf Spot)[5][6][7][8][9] The infection can be diagnosed by the following:

• Yellowing of leaves
• Small (2-5mm), angular, water-soaked lesions on foliage with chlorotic halos and tan or brown centers
• Eventual necrosis of lesions
• Blue-green fluorescence in cultivation

Overwatering and stress increase plant susceptibility.

In Cannabis, P. cannabina pv. cannabina causes stem and leaf rot of both industrial (hemp) and horticultural plants, producing similar symptoms to those observed in crucifers. Despite the fact that Pseudomonas bacterial blight is the most commonly documented disease of cannabis plants,[9][10] the chlorotic lesions are often mistaken by horticultural growers for those of overwatering, nitrogen deficiency, phosphorus deficiency, or Septoria.[11][12]

Bacterial blight caused by P. cannabina pv. alisalensis has been reported in Greece, Germany, Australia, Japan, and several regions of the US including the Midwest, South, and Pacific Coast. Though some of these identifications were mislabeled as P. syringae pv. alisalensis, the indication that P. cannabina pv. alisalensis has a wide, intercontinental distribution is clear.[5][6][7][8] The distribution of P. cannabina pv. cannabina is less obvious, because the fluctuating legal status of the host plant creates difficulty in researching the disease, though it is frequently referred to as a common bacterial blight in the available cannabis horticulture literature.

Bacterial blight in both hemp and crucifers is encouraged by cool, wet conditions in the range of 12–28 °C (54–82 °F), and is spread by water through irrigation of crops with a potential for seed transmission as well.[9][13][14]