Microscopical studies of resistance to powdery mildew disease in the hop cultivar Wye Target

Abstract

Microscopical studies of fungal development and host responses during infection of the hop cultivars Northern Brewer (susceptible) and Wye Target (resistant) with a Zenith isolate of Sphaerotheca humuli are described. Resistance to powdery mildew disease in cv. Wye Target is principally determined by the R2 major gene. Fungal growth was typically restricted in cv. Wye Target following formation of a single haustorial initial or haustorium which failed to develop the characteristic lobes found in susceptible cells. The hypersensitive reaction of penetrated epidermal cells was associated with death of haustorial initials but the associated appressorium remained alive during the first 2 days after inoculation. In leaves expressing resistance, histochemical staining revealed deposition of lignin‐like material and callose in penetrated cells and to a lesser extent in underlying palisade mesophyll cells. Transmission electron microscopy and enzymic digestion clearly demonstrated extensive paramural deposition of β‐1.3 glucans (callose) in reacting mesophyll cells. Plant cell death, lignification and widespread callose deposition were rarely observed at infection sites in cv. Northern Brewer but collars of callose were deposited around the necks of all haustoria formed.

Étude comparée des premières étapes de l'infection chez des bananiers sensibles et résistants infectés par le Cercospora fijiensis (Mycosphaerella fijiensis) agent responsable de la maladie des raies noires

“…Yangambi, aprks coloration par le bleu d'aniline, les cellules situCes autour des sites de penetration stomatiques montrent une fluorescence jaune dks le 8eme jour. Cette fluorescence, nettement localis~e au niveau des parois des cellules hbtes, rappelle celle dCjB dCcrite pour d'autres interactions (Goodwin et al 1987;Gees et Hohl 1988). Le bleu d'aniline est souvent utilisC comme un indicateur de la prCsence de callose (Eschrich et Currier 1964).…”

Biological control of Podosphaera xanthii the causal agent of squash powdery mildew disease by upregulation of defense-related enzymes

“…Conidial spores of squash powdery mildew were obtained from young sporulating lesions. To avoid the old unviable conidia, the lesions were gently shaken by a glass rod, and 24 h later (as recommended by (Godwin et al 1987), new conidia were deposited on glass slides according to Nair et al (1962). Slides were previously cleaned by ethyl alcohol and air dried before covering with thin smears of 2% water agar, amended with filter-sterilized culture filtrate of the tested antagonist.…”

The assessment of partial resistance to powdery mildew disease in hops

“…Such a combination may explain the durability of the resistance shown by cv. Wye Target (Godwin et at. 1987).…”

“…Zenith, which possesses three major resistance genes (RB, Ri, R3) that are no longer effective in the field. To ensure the integrity of the pathotype, it was maintained according to the procedures described by Godwin et al (1987). Plants of other genotypes possessing resistance determined by the known major genes RB, RI, R2, R3, R4 and R5 (Godwin, 1985), together with the parental genotypes, were also included in the test.…”

“…Currently, only cv. Wye Target, which was introduced in 1972 and possesses the R2 gene, continues to exhibit effective resistance in the field (Godwin et al, 1987). Other hop cultivars with major gene resistance have been found to be highly susceptible to new pathotypes (Neve & Darby, 1982).…”