Ascochyta diseases of pea

Ascochyta Diseases of Pea

Ascochyta diseases of pea are caused by a complex of fungal pathogens including Ascochyta pisi, Mycosphaerella pinodes (teleomorph of Ascochyta pinodes), and Phoma medicaginis var. pinodella (syn. Ascochyta pinodella). These diseases are among the most significant factors affecting pea (Pisum sativum) cultivation worldwide, leading to considerable yield losses and quality degradation. The diseases manifest as leaf spots, stem cankers, and foot rot, severely impacting plant health and productivity.

Symptoms

The symptoms of Ascochyta diseases in peas vary depending on the pathogen involved but generally include:

• Leaf spots: Circular to irregular brown or black spots, often with a yellow halo, appearing on leaves and pods.
• Stem cankers: Dark, sunken lesions on stems and branches, which can girdle the stem and cause plant death.
• Foot rot: Darkening and decay of the stem base, leading to plant lodging and death.

Etiology

The Ascochyta complex involves three main fungal pathogens:

• Ascochyta pisi is responsible for Ascochyta blight, primarily affecting leaves and pods.
• Mycosphaerella pinodes (anamorph Ascochyta pinodes) causes blight and spot symptoms on all aerial parts of the plant.
• Phoma medicaginis var. pinodella (formerly Ascochyta pinodella) leads to foot rot and stem cankers.

These fungi overwinter in infected plant debris and soil, spreading through rain splash and wind. The disease cycle is completed when spores land on susceptible tissue, germinate, and penetrate the plant, leading to infection.

Management

Integrated disease management strategies are crucial for controlling Ascochyta diseases in peas. These include:

• Cultural practices: Crop rotation with non-host crops for at least four years, removal and destruction of infected plant debris, and avoiding sowing in fields with a history of Ascochyta diseases.
• Resistant varieties: Use of pea varieties with genetic resistance to one or more of the Ascochyta pathogens.
• Chemical control: Application of fungicides may be necessary, especially during wet weather conditions conducive to disease development. It is important to follow label recommendations and integrate chemical control with cultural practices to manage resistance.

Research and Breeding

Ongoing research focuses on understanding the genetics of resistance to Ascochyta diseases in peas, developing more resistant pea varieties, and improving disease management practices. Breeding efforts aim to combine resistance to multiple pathogens within the Ascochyta complex, ensuring durable protection against this disease.

Economic Impact

Ascochyta diseases can cause significant economic losses in pea production due to reduced yield and quality. The cost of management practices and the potential need for chemical control measures add to the economic burden on growers.

Conclusion

Ascochyta diseases of pea represent a complex challenge requiring integrated management strategies. Advances in breeding for resistance, along with effective cultural and chemical control measures, are key to mitigating the impact of these diseases on pea production.