Interactions of four pathotypes of Diplocarpon rosae with species and hybrids of Rosa

Abstract

The interactions of four pathotypes of Diplocarpon rosae with 34 species and hybrids of Rosa were compared in an ongoing search for criteria of potential relevance to rose breeding. There were greater similarities in the resistance-susceptibility interactions of these roses to the pathotypes DA1, CW1 and ZM1, than to a fourth pathotype, DA2. Among the species roses, only those of the section Cinnamomeae were susceptible to DA2 and this susceptibility was transmitted in several cases to hybrid progeny. CW1 had the greatest pathogenicity of the four pathotypes. In a cross between R. rugosa cv. Scabrosa, which was resistant and R. rugosa f. alba, which was susceptible to all pathotypes, the progeny were tested for resistance to pathotypes DA1, CW1 and ZM1. Each of the 20 progeny was susceptible to all three pathotypes. This shows that, unlike the well characterized Rdr1 gene for resistance to D. rosae, the resistance of R. rugosa cv. Scabrosa is not determined by a dominant major gene. The diploid hybrid, R. rugosa cv. Martin Frobisher · cv. Mistress Quickly, was resistant to all four pathotypes, but an induced tetraploid of this hybrid was susceptible to all pathotypes. The relevance of these findings to the breeding of roses for resistance to black spot disease is discussed.

A standard set of host differentials and unified nomenclature for an international collection of Diplocarpon rosae races

“…Therefore, the existence of a twelfth race is postulated based on previous results, though this could not be confirmed. Yokoya et al (2000) and Allum et al (2010) showed that isolate DA2 had the most striking host range. The only species roses it infected were those of the section Cinnamomeae, but some Cinnamomeae hybrids, including R. rugosa hybrids, were also susceptible.…”

“…Four races from the UK were also discovered (Yokoya et al. , 2000; Allum et al. , 2010), and four races were differentiated in Belgium (Leus, 2005).…”

“…Detached leaf inoculations were used to differentiate five races of D. rosae originating from Germany . Four races from the UK were also discovered (Yokoya et al, 2000;Allum et al, 2010), and four races were differentiated in Belgium (Leus, 2005). Most recently, three races were reported from eastern North America (Whitaker et al, 2007a).…”

Characterization of black spot resistance in diploid roses with QTL detection, meta-analysis and candidate-gene identification

“…The highly heterozygous nature of Rosa species is a complicating factor when it comes to genetic mapping. The pseudo-test cross mapping approach (Grattapaglia and Sederoff 1994;Kirst et al 2004;Adam-Blondon et al 2016), developed for highly heterozygous species, allows development of parental maps that are then combined into an integrated map. However, (Gartner et al 2013) showed that, although integrating homologous chromosomes that have been rearranged can produce mathematically and statistically correct maps, they do not necessarily reflect the biological reality of chromosomal rearrangements and meiotic recombination that had happened during the outbred cross.…”

Construction of a genetic linkage map with SSR, AFLP and morphological markers to locate QTLs controlling pathotype-specific powdery mildew resistance in diploid roses

“…Of the more than 140 species in the genus Rosa belonging to the Rosaceae family, (Wissemann 2003;Gudin 2000) only 11 of them are likely to have contributed to the origin of modern cultivars (Gudin 2000). Ploidy levels in roses differ from diploid (2n = 2x = 14) to octoploid (2n = 8x = 56) but modern roses are often tetraploids (2n = 4x = 28) (Roberts et al 2009;Allum et al 2010;Debener and Linde 2009). Rose chromosomes are small; the 2C DNA amount in diploid roses (2n = 2x = 14) ranges from 0.83 to 1.30 pg (Roberts et al 2009).…”