MOLECULAR ANALYSIS OF THE NEW ZEALAND POPULATION OF VENTURIA INAEQUALIS
J PATTERSON1,2, KM PLUMMER1,2, JK BOWEN1 and RD NEWCOMB1
1HortResearch, Mt Albert Research Centre, Private Bag 92169, Auckland, New Zealand; 2University of Auckland, Private Bag 92019, Auckland, New Zealand
Background and objectivesVenturia inaequalis causes apple scab, the most commercially important fungal disease of apple worldwide. It causes lesions on leaves and fruit, reducing both quality and quantity of the harvest. Currently, none of the commercial apple cultivars used in New Zealand (NZ) are resistant to the disease and control in the orchard relies on a rigorous fungicide regime. Breeding resistance to V. inaequalis into commercial apple cultivars is a major focus of apple breeding programmes worldwide. Successful deployment of resistance requires an in-depth understanding of the variation in the pathogen population. Seven races of V. inaequalis have been identified. Little is known about the variation in the NZ V. inaequalis population, but only one race (race 1) has been detected. A preliminary study using RAPD analysis showed an extremely high degree of variation in the fungus in NZ; no two isolates had the same RAPD banding pattern. This was not entirely unexpected since V. inaequalis reproduces sexually every growing season. We have extended the survey of NZ population to include more growing regions, closely related isolates from apple and isolates from crab apples. These were compared with isolates from Northern Hemisphere populations. In the present study, we used both RAPDs and ribosomal DNA (rDNA) sequence analyses to characterize genetic variation at the molecular level.
Materials and methodsMonoconidial V. inaequalis isolates were collected from individual lesions on infected leaves and fruit. Host material included different apple and crab apple cultivars from the Auckland region and from various apple-growing regions in NZ (to maximum distance of approximately 1000 km). The isolates from crab apple were included to determine whether ornamental trees could host a different subpopulation of V. inaequalis. Crab apple species are also the major source of resistance genes currently being used in apple breeding programmes.
Results and conclusions