2.3. Powdery mildew
Powdery mildew (Fig. 2) is the most common and severe disease in cut rose production as this protected environment provides excellent growth conditions for this fungus as well as the plant. It is also regionally important in field grown roses [15], [46], [47] and [48]. This is an obligate fungal parasite which has multiple pathogenic races interacting with the various cultivars [49], [50], [51] and [52]. Although the sexual stage is occasionally seen (∼5% of those examined) there is a high diversity of pathogenic races within individual fields [51] and [53]. Furthermore, Podosphaera has airborne conidia which can be transported longer distances than a pathogen such as Diplocarpon which is spread mainly via water splash. This heightens the potential of new races forming and spreading rapidly.
Sources of resistance have been identified in both cultivated and wild roses [39], [54] and [55]. Various pathogen–host interactions have been described which showed the range of reactions from rapid penetration and growth/sporulation to a hypersensitive reaction and reduced spore germination [56]. Subsequent genetic tests indicated that both vertical resistance conditioned by a dominant resistance gene (Rpp1) [51] and horizontal (partial) resistance conditioned by multiple genes [57], [58], [59], [60], [61] and [62] are operational.
2.3. Powdery mildew
Powdery mildew (Fig. 2) is the most common and severe disease in cut rose production as this protected environment provides excellent growth conditions for this fungus as well as the plant. It is also regionally important in field grown roses [15], [46], [47] and [48]. This is an obligate fungal parasite which has multiple pathogenic races interacting with the various cultivars [49], [50], [51] and [52]. Although the sexual stage is occasionally seen (∼5% of those examined) there is a high diversity of pathogenic races within individual fields [51] and [53]. Furthermore, Podosphaera has airborne conidia which can be transported longer distances than a pathogen such as Diplocarpon which is spread mainly via water splash. This heightens the potential of new races forming and spreading rapidly.
Sources of resistance have been identified in both cultivated and wild roses [39], [54] and [55]. Various pathogen–host interactions have been described which showed the range of reactions from rapid penetration and growth/sporulation to a hypersensitive reaction and reduced spore germination [56]. Subsequent genetic tests indicated that both vertical resistance conditioned by a dominant resistance gene (Rpp1) [51] and horizontal (partial) resistance conditioned by multiple genes [57], [58], [59], [60], [61] and [62] are operational.
การแปล กรุณารอสักครู่..
