Morphologische und molekulare Charakterisierung des Pathogens <em>Colletotrichum gloeosporioides</em> an <em>Gaultheria</em> mit dem Ziel der Erschließung von Resistenzquellen

Abstract

Gaultheria procumbens L. is an important horticultural species in Germany. It is cultivated and used as an ornamental plant for the fall season. The perennial and hardy Ericaceous shrub propagates via seeds and rhizomes. Over the last years, German Gaultheria producers have suffered from enormous losses up to collapses of the whole crop due to the infection with the fungus Colletotrichum gloeosporioides. Only frequent applications of fungicides in the juvenile phase prevent the expansion of the pathogen. In older plants the application of fungicides is less effective and preventive, since the fungus colonizes the lower stem part which cannot be reached by fungicides. An alternative to the application of fungicides is the use of plant genetic resources as disease resistance donors and the development of resistant cultivars. Therefore, the focus of this work was (1) on the collection, maintenance, reproduction and hybridization of different Gaultheria species, on (2) the characterization of the pathogen for the development of a reproducible and practicable resistance test as well as (3) on the evaluation of resistance in selected Gaultheria species. Overall, out 23 of 33 Gaultheria species cultivated in the greenhouse were successfully established on Anderson's medium as in vitro shoot cultures. In further cultivations on Anderson's medium supplemented with phytohormons (9 μM/l zeatin, 5,7 μM/l indole-3-acetic-acid) more shoots were successfully established from shoot segments than from shoot tips. Genetic relationships in the genus Gaultheria were analysed using 185 Random Amplified Polymorphic DNA markers and formed the basis for interspecific hybridisations. Three interspecific hybrids of G. myrsinoides x G. procumbens were molecularly identified by RAPD markers. Studies on the long-term storage of Gaultheria pollen in vitro revealed that pollen from G. procumbens stored for up to three months at -20 °C retains 50 % and from G. shallon 70 % germinating rate. With temporal increasing cold storage germinating rate decreased and went to zero after six months. Concerning to the pathogen C. gloeosporioides the morphological and genetic variability plus its virulence potential were investigated. Based on sequence analysis of the rDNA ITS region in comparison to published sequences in the BLAST database, C. gloeosporioides and C. acutatum were shown to infect Gaultheria. Studies on the pathogenic potential confirmed that C. acutatum is non-pathogenic. In a PCR-based detection of C. gloeosporioides in infected Gaultheria plant material no specific amplicons were obtained, when applying additives and touch-down PCR programmes. The evaluation of morphological characteristics such as radial mycelial growth, colony color, and structure of mycelium, setae formation and mass propagation of conidia as well as their length and width indicated huge differences between the 27 tested isolates. Further experiments were performed on latently infected Gaultheria shoots. They demonstrated that the pathogen accumulates mainly in the root zone of the plant. These results formed the basis for substrate infection experiments, in which contaminated substrate led to an infection of Gaultheria plants within four weeks. Resistance tests showed that G. shallon was less susceptible against a highly virulent isolate (P-14) than G. procumbens, G. pumila and G. hispida when applying a spore suspension at the stem base.