Comparison of fire blight resistance screening methodologies

Abstract

Fire blight, a bacterial disease caused by Erwinia amylovora, is an ongoing problem for pipfruit growers, with few control options available. Most commercial cultivars and rootstocks are highly susceptible to the disease. Breeding of fire blight-resistant scions and rootstocks to manage the disease is a major goal of the New Zealand apple breeding programme. The main mode of disease establishment is through flowers. However, the breeding programme currently evaluates disease resistance through shoot inoculations. This study compared the degree of resistance in 109 progeny from a 'Royal Gala' x Malus robusta 'Robusta 5' family assessed by shoot inoculation and by floral inoculations. Results indicate that the two measures of resistance do not correlate well, and that different quantitative trait loci may be involved in flower and shoot resistance. Management of fire blight through the implementation of resistant cultivars will require resistance screening on both shoot and flower assessments.