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ISHS Acta Horticulturae 663: XI Eucarpia Symposium on Fruit Breeding and Genetics

SCREENING METHOD FOR POLYGENIC SCAB RESISTANCE WITHIN AN APPLE BREEDING PROGRAMME: RELATIONSHIP BETWEEN EARLY GREENHOUSE SCREENING TEST ON YOUNG SEEDLINGS AND THEIR SCAB SUSCEPTIBILITY IN NATURAL FIELD CONDITIONS

Authors:   B. Lefrancq, M. Lateur, A. Rondia
Keywords:   Malus x domestica, Venturia inaequalis, artificial inoculation, breeding, early scab screening
DOI:   10.17660/ActaHortic.2004.663.143
Abstract:
Most of the apple cultivars grown commercially are highly susceptible to scab, the most serious apple fungal disease in humid areas. Therefore many breeding programmes are focused on scab resistance. Monogenic sources of resistance, specially the Vf gene, were most often used by the breeders. However, the breakdown of Vf resistance by several scab races emphasizes the importance of broadening the genetic diversity of scab resistance including quantitative resistance. Our apple breeding programme started in 1988 by using local genetic resources. Our objective is to create high quality commercial cultivars carrying durable resistance to scab, powdery mildew and Nectria canker. The breeding strategy is based on the use of old apple cultivars and land-races as parents, selected for low disease susceptibility and possessing other desirable horticultural characters. Unlike the methodology for screening cultivars carrying a major resistance gene, screening for partial resistance is less standardized and not yet well studied. Our project aims to develop an early and efficacious selection methodology adapted to partial disease resistance. The objective is to define the optimal screening limit for discarding individuals after artificial scab inoculation tests. A trial was conducted to assess the relationship between young seedling scab resistance features after inoculation and their resistance under natural field conditions. The results show this relationship under certain conditions. We propose that up to 25% of the leaf surface covered by scab sporulation can be used as the greenhouse selection threshold.

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