Powdery Mildew on Roses: Pathotype Screening

Abstract

Monospore cultures of rose powdery mildew (Sphaerotheca pannosa var. rosae) were established from isolates collected on outdoor grown roses at different locations in Belgium. These monospore cultures were tested on rose cultivars and species with different levels of natural resistance to examine the possible existence of different pathotypes. Therefore a screening protocol including scoring after artificial infection was developed on in vitro plantlets. The calculated disease indexes of the collected monospore cultures on different rose cultivars and species showed that up to now in the collected isolates no evidence of distinct pathotypes could be found. The reaction of plants towards the disease differed greatly between the examined cultivars and species. The test was validated for in vivo circumstances indicating that in vitro rose plants can be used for pathotype and resistance screening.

Isolation and identification of eight races of powdery mildew of roses (Podosphaera pannosa) (Wallr.: Fr.) de Bary and the genetic analysis of the resistance gene Rpp1

“…Five races of S. pannosa out of nine isolates from two sites in the U.S.A. were characterised by Bender and Coyier (1984) with a differential set of five cultivars. Leus et al (2002) could not distinguish any pathotypes from eight isolates sampled at five places in Belgium with a set of seven rose genotypes. In these investigations the infections were made by dusting conidia from infected shoots over the test cultivars or by brushing inoculum onto the test plants, not really securing the inoculation of the leaf material with a similar conidia density in the repeated experiments.…”

“…The use of small differential sets could lead to an underestimation of the racial diversity within the pathogen populations, because of the possibly low number of resistance genes present in these genotypes. Leus et al (2002) used a set of five commercial cultivars, which were infected by all isolates, and two species, from which Rosa laevigata anemoides was also susceptible for all isolates and R. wichuraiana showed only minor infections for two isolates. Only two races of Sphaerotheca fusca on cucurbits were found within 41 isolates from 30 locations in Crete (Vakalounakis and Klironomou 1995).…”

“…Mence and Hildebrandt (1966) also suggested the existence of two separate forms of the fungus, differing in host range and size of conidia. In contrast to these authors, which used mixed inoculum, Bender and Coyier (1984) and Leus et al (2002) established monoconidial isolates. Bender and Coyier identified five races of P. pannosa with a differential set of four rose cultivars out of nine isolates sampled in Oregon (U.S.A.).…”

Assessment of Partial Resistance to Powdery Mildew (Podosphaera pannosa) in a Tetraploid Rose Population Using a Spore-suspension Inoculation Method

“…Two well-defined monospore isolates, isolate 2 from Ahrensburg, Germany (Linde and Debener, 2003) and isolate F1 from Lesdain, Belgium (Leus et al, 2002), were kindly provided by the authors. The monospore isolates were maintained in vitro as described by Linde and Debener (2003).…”

“…Bender and Coyier (1984) identified five races in nine samples from Oregon (USA). Leus et al (2002Leus et al ( , 2003 studied eight isolates collected in Belgium and showed a differential host response, indicating differences in virulence among isolates. Linde and Debener (2003) recently classified eight different races in northern Germany and concluded that the pathogen harbours a high diversity of virulence genes.…”