Evaluation of Daphne Germplasm for Resistance to Daphne Sudden Death Syndrome Caused by the Soil-borne Pathogen Thielaviopsis basicola

Abstract

<jats:p>Many daphne cultivars are susceptible to fungal root pathogens and require frequent fungicide applications during production. To identify taxon differences to disease susceptibility, we evaluated 32 <jats:italic>Daphne</jats:italic> species and cultivars for resistance to the soil-borne pathogen, <jats:italic>Thielaviopsis basicola</jats:italic> (Berk. and Broome) Ferr., by both in vitro- and in vivo-based methods. Disease-free plant roots were inoculated with the pathogen through topical application of a spore suspension and observed weekly for disease development/progression. Significant variation for disease severity among the taxa evaluated was determined using a plant disease index. Plant reactions ranged from highly resistant, e.g., <jats:italic>D. tangutica</jats:italic> and <jats:italic>D. retusa</jats:italic>, to highly susceptible, e.g., <jats:italic>D. cneorum</jats:italic>. In addition, a high correlation was found between the in vitro and in vivo techniques for the seven selected species, indicating that they are comparable. However, the in vitro assay provided results in significantly less time than the in vivo assay.</jats:p>

In vitro propagation of seven Daphne L. species

“…Our results didn't show any strong correlation between the geographic origin/the size of the original plants and their response to the media composition (see Noshad et al 2007). For example D. cneorum and D. jasminea responded relatively similar to the most of media examined while they are from two separate geographical origins-D. cneorum from Europe and D. jasminea from SW China.…”

“…Reports indicate that one of the major limitations to Daphne's survival in cultivation is susceptibility to fungal root pathogens that cause root rot and chlorosis (Noshad et al 2007). In addition to fungal pathogens, many viral diseases have been reported in Daphne.…”

“…However, these species were successfully ''revitalized'' by producing disease-free stock plants through tissue culture techniques, thereby eliminating most of the endophytic pathogens (Jayasankar et al 2001;Chen et al 1995). Although in vitro techniques successfully generated disease-free plants in a relatively short time period in D. odora (Marks 1997), Daphne species remain very difficult to establish and manipulate in culture (Noshad et al 2007). Furthermore, browning of tissues and hyperhydricity (or vitrification) are reported to be problematic during in vitro propagation of several Daphne species (Chen et al 1995;Wang and Tang 1994;Cohen 1977).…”

“…Reports (Preece and Compton 1991;Escobar and Villalobos 1986;Krulik 1980) suggest hyperhydricity could result from the type and concentration of cytokinins, gelling agent, or medium used and the cultures usually became vitrified more often on media with high concentrations of cytokinins, particularly with TDZ. Part of the problem with browning of the tissues appears to be associated with significant speciesspecific culture requirements, type and amount of plant growth regulators and the presence of polyphenol oxidases in Daphne tissue that cause explant browning and death during establishment and acclimatization stages (Marks and Simpson 2000;Green et al 1992;Cohen 1977;Noshad et al 2007). Therefore, the development of species-specific in vitro protocols is needed to allow for the production of uniform, disease-free plants for commercial and experimental use (Krogstrup and Norgaard 1991;Bennett and Davis 1986;.…”

Epicuticular wax content of western white pine is involved in Cronartium ribicola resistance

“…To study mechanisms of resistance, we used wax removal techniques and electron microscopy to investigate characteristics of epicuticular wax and its impact on stomata's morphology in our resistant families, as utilized by previous researchers (Smith et al, 2006). These techniques can offer a powerful alternative for defining specific types of resistance vs. avoidance and identifying valuable resistant genotypes (Klimaszewska et al, 2007; Noshad et al, 2007; Park & Klimaszewska, 2003).…”