Science into practice - Identifying mildew sources

Project HNS 196 Identification of inoculum sources for the newly emerged Peronospora causing downy mildew on aquilegia.

Aquilegia downy mildew is caused by a currently unnamed species of Peronospora. Since its occurrence was first reported in 2011, the disease has become more widespread within the industry, causing plant losses on nurseries and in gardens.

Plant symptoms include angular yellow patches on leaves, which eventually turn brown, and purple fungal growth that can often be seen on the underside of infected leaves. Under the right conditions, the disease can spread quickly and could lead to rapid plant death. Identifying infection pathways will assist the development of effective management strategies to minimise future plant losses from this disease.

Project HNS 196 aims to determine whether the pathogen is a seed-borne disease. Seed samples used for testing within the trial were selected based on the results of a questionnaire sent out to aquilegia growers within the industry.

Analysis of the seed revealed that one batch contained spores of the pathogen, suggesting that Peronospora could potentially be seed-borne. Further molecular-based tests are being carried out to confirm this.

High humidity, leaf wetness and a minimum temperature are generally required for downy mildew infections to take hold within crops. Using the infected seed batch, growth tests are now establishing whether the presence of the spores results in the disease actually taking hold on the plant. Three different watering regimes (sub-irrigation and overhead irrigation applied in the morning or afternoon) are also being tested to see whether cultural control is possible.

A follow up trial, HNS 196a, is currently investigating fungicide control options for aquilegia downy mildew.

AHDB Horticulture

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