Resistance of roses to pathotypes of Diplocarpon rosae

Abstract

SummaryColonies of Diplocarpon rosae derived from single conidia were isolated on malt extract agar, multiplied (at 23°C) and stored (at −20°C) on surface‐sterilised leaf discs of a universally susceptible rose, ‘Frensham’. The resistance of 16 species and cultivars of Rosa to different isolates of D. rosae was assessed using surface‐sterilised leaf discs. Four pathotypes of D. rosae were distinguished on the basis of host range. One species and one hybrid were resistant to all pathotypes. Two species and two cultivars were susceptible to all pathotypes. Four species and six cultivars were interpreted as having vertical resistance because they were strongly resistant to some but not all pathotypes. Only species and hybrids of the section Cinnamomeae were resistant to the pathotype identified as CW1 whereas only roses of other origins were resistant to the pathotype DA2.

Partial resistance to black spot disease in diploid and tetraploid roses: general combining ability and implications for breeding and selection

“…In rose this has phenotypically been observed as reduced lesion size, reduced sporulation, and/or delayed onset of infection (Xue and Davidson 1998). In contrast, major gene resistance in rose is complete and is easily distinguishable due to the absence of sporulation and mycelial growth von Malek and Debener 1998;Whitaker et al 2007a;Yokoya et al 2000). In 15 of the 16 populations in our study, sporulating lesions were observed on all plants.…”

“…Thus far, these measures have only been applied to inoculation studies of whole plants, as opposed to detached leaves (Whitaker et al 2007a). Detached leaf assays and leaf disc assays with single-spore isolates have been successfully used for race determinations and screening of major genes Von Malek and Debener 1998;Yokoya et al 2000). Jenkins (1955) reported a near-perfect correlation coefficient (r = 0.97) in a comparison of lesion sizes in detached leaflet and whole plant assays for four cultivars and one species inoculated with three isolates of D. rosae.…”

“…The damage to plant health and appearance that results from defoliation is what makes black spot the most serious disease of roses in the outdoor landscape (Dobbs 1984). The high cost and perceived environmental risk of preventative fungicidal sprays for black spot control has increased the demand for resistant cultivars (Yokoya et al 2000).…”

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

“…Whereas black spot is considered to be the most severe disease of field-grown roses (Horst 1983;Debener et al 1998;Malek von and Debener 1998;Yokoya et al 2000), powdery mildew is the major fungal pathogen of roses grown in greenhouses (Horst 1983;Linde and Shishkoff 2003). There have been many reports on the development, epidemiology and host -parasite relationship of P. pannosa in which the environmental and cytochemical aspects of the infection process and the defence reaction of the rose were described.…”

Survey and Pathogenicity of Black Spot Disease of Rose in Pakistan

“…Since, leaves of rose plants raised in glasshouses present in the temperate zones may be kept dry; therefore these plants are not severely infected by black spot disease [13,19]. Different pathotypes of D. rosae have been illustrated using polyconidial [20] and monoconidial [21,22] isolates. Furthermore, different morphotypes have also been observed [23].…”