ISHS Acta Horticulturae 725: V International Symposium on In Vitro Culture and Horticultural Breeding
AGGRESSIVENESS OF PHYTOPHTHORA INFESTANS ISOLATES CORRELATES WITH THEIR PROTEOLYTIC ACTIVITY |
| Authors: | J.A. Hamill, C. Selby, L.R. Cooke |
| Keywords: | potato, late blight, serine protease, cysteine protease |
| DOI: | 10.17660/ActaHortic.2006.725.93 |
| Abstract:
In Northern Ireland, late blight, caused by the oomycete plant pathogen Phytophthora infestans, causes substantial yield losses in potatoes (Solanum tuberosum) in most years despite intensive fungicide use. In many plant-pathogen relationships, proteases aid colonisation of the host. By understanding the involvement of proteases in pathogenicity, it may be possible develop plant breeding strategies to create durably resistant potato cultivars. In this study, the correlation between cysteine protease and serine protease activities and the pathogenicity of P. infestans isolates was investigated. The aggressiveness of nine isolates, seven from Northern Ireland, one from Mexico and one from the USA (US-8 clonal lineage) was assessed on detached leaflets of the potato cultivars ‘Bintje’ (susceptible) and ‘Stirling’ (partially field-resistant) by measuring lesion area and calculating the area under the lesion expansion curve (AULEC). Extracts of mycelium were assayed for serine protease and cysteine protease activities using N-benzoyl-L-tyrosine ethyl ester (BTEE) and  -N-benzoyl-DL-arginine 2-napthylamide HCl (BANA), respectively as substrates.
A significant positive correlation (r = 0.732) was found between serine protease specific activity and the aggressiveness of P. infestans isolates.
However, there was no correlation between cysteine protease specific activity and isolate aggressiveness.
Serine proteases therefore appear to be an important pathogenicity factor influencing the aggressiveness of P. infestans isolates.
Inhibition of these enzymes by breeding potato cultivars for enhanced levels of natural serine protease inhibitors, using either genetic manipulation or molecular-marker-based methods, may provide an improved way to combat late blight in potatoes and reduce dependence on fungicides.
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