Occurrence of White Top of Pea Caused by a New Strain of Pseudomonas syringae pv. pisi

The epidemiology and management of bacterial blight (Pseudomonas syringae pv. pisi) of field pea (Pisum sativum) in Australia: a review

Bacterial blight caused by Pseudomonas syringae pv. pisi is an important, but sporadic, disease of field peas (Pisum sativum) in Australia. The presence of P. syringae pv. pisi reduces the profitability of peas due to yield loss and, in some cases, it also limits Australia’s export of peas to some countries. Pseudomonoas syringae pv. pisi is primarily a seed-borne pathogen, but infected pea trash can be an important source of inoculum. Alternative hosts and soil are not regarded as epidemiologically important sources of inoculum. P. syringae pv. pisi survives, multiplies and spreads epiphytically in pea crops. Epiphytic populations of P. syringae pv. pisi only become pathogenic following crop damage caused by frost or severe weather conditions. Frost damage is especially important because the ice nucleating activity of P. syringae pv. pisi initiates frost damage at higher temperatures than occurs in the absence of the bacterium. In addition early-sown crops are more prone to damage from bacterial blight than crops sown later in the season. Pseudomonas syringae pv. pisi consists of seven identified races. One of these (Race 6) lacks all avirulence genes and is common around the world and in Australia. Globally, Race 2 and Race 6 predominate; however, in Australia, Race 3 predominates due to the widespread cultivation of cultivars susceptible to Race 3, but resistant to Race 2. Resistance to Race 6 within P. sativum has not been found but attempts are being made to incorporate a race non-specific resistance identified from P. abyssinicum into field pea. Bacterial blight can be successfully controlled using an integrated disease management strategy incorporating crop rotation, pathogen-free seed, avoidance of planting in areas prone to frequent frosts or extreme wet weather, crop hygiene and avoiding early sowing. Seed treatment and application of foliar bactericides have limited use in control of this disease.