Bundessortenamt

The grey mould disease caused by Botrytis cinerea leads to substantial economic losses in strawberry production all over the world. Control of the disease requires an extensive amount of fungicide that is applied in varying complexes because the pathogen easily develops resistance against the active compounds. Planting of resistant cultivars seems to be a promising alternative for fruit growers, but there are currently no cultivars available combining resistance to B. cinerea with attractive horticultural traits. Breeding of new cultivars requires the effective identification of resistant strawberry genotypes; therefore the current study was aimed at the evaluation of strawberry genetic resources under controlled conditions by establishing an artificial inoculation assay. The method presented in this study is an artificial inoculation of ripe fruits with a defined spore suspension under laboratory conditions. The results show that this assay is fast and simple and leads to reproducible results that correlate with field observations. Over 3 years a total of 107 strawberry genotypes of the German National Fruit Genebank at the JKI in Dresden‐Pillnitz were evaluated. Five partly resistant genotypes, cultivars Diana, Joerica and Kimberly, and Fragaria virginiana ‘Wildmare Creek’ and F. vesca subsp. bracteata , were identified with mean disease levels of <20% at 6 days post‐inoculation. The obtained results are discussed with regard to future breeding activities.

Raspberry is an attractive fruit crop due to high market prices for producers and good future market prospects because of its image as health food. However, German production only covers 10% of its consumption. This can be attributed to high yield losses caused by fungi that make raspberry production unprofitable in later years of planting. Cane diseases are caused by a mixture of several fungi and can hardly be managed with chemical plant protection. The main causal agent varies by cultivation area. The goal of this project is to build a basis for a raspberry breeding program for cane disease resistance with good climatic adaptation for Germany. A field evaluation of over 200 cultivars was conducted in three locations for three years to find suitable parents for resistance breeding. Variation in resistance from almost no infestation (Tayberry) to symptoms on over 76% of the cane surface (Delmes) was found. Furthermore, test crossings were conducted to determine the heritability of the resistance, resulting in populations for mapping and for breeding. Artificial inoculation was established as a method for easier testing of future progeny. For this, the main cause of the disease in Saxony had to be identified through isolation of the fungi found on diseased canes. 24 isolates were identified by macroscopic and microscopic examination in addition to DNA testing. After evaluation of the resulting pathogen strain library, Fusarium avenaceum was found to be the main cause of cane disease in these three locations. As a result of the project, there are already two breeding clones with good tolerance towards cane disease and good yield and fruit properties under testing as cultivar candidates. In the future, QTL mapping will be performed on a bi-parental mapping population after phenotyping for resistance under natural conditions in the field as well as in vitro inoculation and artificial infection in the glasshouse. Additionally, association mapping will be conducted through GBS (Genotyping by Sequencing) on the existing raspberry variety pool to find the gene responsible for field resistance. The resulting markers associated with cane disease resistance will be particularly valuable by accelerating resistance breeding.