Status of breeding for Apple Scab resistance in Australia

Abstract

In Australia, breeding for resistance to the apple scab fungus Venturia inaequalis was commenced by the Queensland Department of Primary Industries (QDPI) in 1985 at Applethorpe Research Station (ARS), located in southern Queensland (latitude 28°37’S) at an elevation of 870 metres. Average annual rainfall is 800 mm, 71% of which occurs during the growing season (October to April). Apple scab is a major problem, and ten to twelve scab infection periods occur during the spring of most years. Fifteen scab resistant varieties and unnamed selections incorporating the Vf gene complex derived from Malus floribunda, and one selection with Vm resistance from M. atrosanguinea, have been introduced into Australia for use in the breeding program. A population of over 77,000 seedlings has been produced from more than 200 crosses. All seedlings were inoculated with Queensland isolates of V. inaequalis and screened for resistance. Previous work by QDPI using scab isolates from a limited number of Australian apple producing districts concluded that only race 1 of the fungus is present in Australia. 18,000 seedlings that were wholly or partly resistant to apple scab have been field-planted at ARS, and continue to be evaluated for fruit quality. The breeding program adopts a three-stage process for progression of breeding lines to commercial testing, and relies on local grower input at all stages. Grower evaluation of selections using a national infrastructure will be a feature of future work. In order to facilitate rapid adoption by industry, tree management packages need to be developed which define the agronomic requirements of a number of superior scab-resistant selections with potential for commercial release. The performance of the Australian breeding program is reviewed with respect to the breeding strategy adopted using Vf resistance, the families of crosses produced, and the fruit quality requirements of the Australian apple industry.