Pectobacterium polaris causes stem soft rot of potato in Mexico and is pathogenic to various vegetables

Aerial potato stem soft rot is an emerging disease in Sinaloa, Mexico, that occurs during the fall– winter season in fields watered by sprinkling irrigation systems, which create prolonged leaf wetness periods ranging from 12 to 18 h when the temperature varies from 18–29°C. The initial disease symptoms occur at the bulking stage, and the incidence reaches up to 10% with maceration of the stems. Multigene phylogenetic analysis and biochemical tests were used to identify the bacterium associated with the disease as Pectobacterium polaris. The pathogenicity of two strains of this bacterium was determined in potato, lettuce, cauliflower, orange habanero pepper, tomato, carrot, zucchini squash and garden bean plants under greenhouse conditions, as well as in detached tubers and tomato fruit, zucchini squash, carrot taproots, garden bean pods and onion bulbs in the laboratory, suggesting that the bacterium has the potential to attack these vegetable crops grown in Sinaloa. This is the first report of P. polaris causing aerial stem soft rot of potato in Mexico. This study identifies a significant new threat to vegetable production in the region, highlighting the need for future research on disease management strategies, which should address the phenological stage in which potato exhibits the highest susceptibility to the pathogen, and the climatic conditions that favour disease incidence. This will contribute to the control of the disease, to the benefit of potato growers.