ISHS Acta Horticulturae 538: Eucarpia symposium on Fruit Breeding and Genetics
SCREENING OF PEAR CULTIVARS FOR RESISTANCE TO FUNGAL DISEASES (Venturia pirina, Nectria galligena) |
| Authors: | H. Kemp, M.C.A. van Dieren |
| Keywords: | pear scab, fruit-tree canker, Podosphaera leucotricha, Gymnosporangium spp., natural infection, varietal specific strains, mites, pomological value |
| Abstract:
Each year, 15 to 20 new pear cultivars are planted in variety trials at Wilhelminadorp/Randwijk, that comprises one replicate without any fungicide application. In this plot, incidence and severity of scab, powdery mildew and fruit-tree canker symptoms on leaves, fruits and/or wood are recorded. In the spring of 1994 and 1995, 69 old and new cultivars were planted at Wilhelminadorp. Since the spring of 1996, over 100 cultivars have been planted at the new experimental site in Randwijk (near Wageningen). Here, only the results from Wilhelminadorp are given. In 1994, no scab was found. Therefore, from 1995 till 1997, scabbed leaves and/or branches from different sources were brought into the plot to increase infection pressure. Again, in 1995, no scab was found on the leaves and almost none on the fruits and in 1996, only with 6 cultivars few scab lesions were observed on leaves and fruits. However, from 1997 till 1999, a steady increase in the number of injured varieties and also in the severity of the scab symptoms was observed. In 1999, still one third of the cultivars was relatively free of scab on fruits and leaves. However, considering the scab occurrence in other trials and practical farms, we consider that at least a part of the scab free or slightly infected cultivars are partly susceptible. This phenomenon is probably due to the slow development of the inoculum and possibly also to the influence of varietal specific scab strains. Until 1999, mildew and canker have incidentally occurred. Now, after 5 to 6 years, susceptible genotypes can be determined, but for a clear distinction between resistant and moderately resistant genotypes for scab, mildew and fruit-tree canker, an observation period of at least 7 to 10 years is required. However, due to the closure of Wilhelminadorp, the trial had to be finished at the end of 1999, but the work will be continued at Randwijk. | |
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