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The plant resistance activator acibenzolar‐S‐methyl (BTH), the signalling molecules salicylic acid (SA) and methyl jasmonate (MeJA) were tested by seed treatment for their ability to protect melon seedlings from gummy stem blight and white mould disease caused by the soil‐borne fungal pathogens Didymella bryoniae and Sclerotinia sclerotiorum, respectively. Didymella bryoniae infection on melon seedlings was completely suppressed by MeJA treatment. Necrotic lesions akin hypersensitive response occurred on all inoculated seedlings and prevented pathogen diffusion into healthy tissues. Didymella bryoniae infection was restricted following BTH seed treatment as well, although the percentage of necrotic lesions in comparison with the water soaked lesions was significantly lower than that from MeJA‐induced seedlings. BTH protected melon seedlings against S. sclerotiorum by the occurrence of a high percentage of necrotic lesions. A lower level of resistance was also achieved by MeJA seed treatment. The augmented level of resistance of tissues from BTH and MeJA‐treated seeds was associated with rapid increases in the activity of the pathogenesis‐related proteins chitinase and peroxidase. MeJA also determined a rapid and transient accumulation of lipoxygenase. Moreover, BTH and MeJA treatments determined the differential induction of particular de novo synthesized isoenzymes of these proteins. Results indicate that BTH and MeJA applied to melon seeds may activate on seedlings diverse metabolic pathways leading to the enhancement of resistance against distinct pathogens.

We report a role for the Arabidopsis (Arabidopsis thaliana) RESURRECTION1 (RST1) gene in plant defense. The rst1 mutant exhibits enhanced susceptibility to the biotrophic fungal pathogen Erysiphe cichoracearum but enhanced resistance to the necrotrophic fungal pathogens Botrytis cinerea and Alternaria brassicicola. RST1 encodes a novel protein that localizes to the plasma membrane and is predicted to contain 11 transmembrane domains. Disease responses in rst1 correlate with higher levels of jasmonic acid (JA) and increased basal and B. cinerea-induced expression of the plant defensin PDF1.2 gene but reduced E. cichoracearum-inducible salicylic acid levels and expression of pathogenesis-related genes PR1 and PR2. These results are consistent with rst1's varied resistance and susceptibility to pathogens of different life styles. Cuticular lipids, both cutin monomers and cuticular waxes, on rst1 leaves were significantly elevated, indicating a role for RST1 in the suppression of leaf cuticle lipid synthesis. The rst1 cuticle exhibits normal permeability, however, indicating that the disease responses of rst1 are not due to changes in this cuticle property. Double mutant analysis revealed that the coi1 mutation (causing defective JA signaling) is completely epistatic to rst1, whereas the ein2 mutation (causing defective ethylene signaling) is partially epistatic to rst1, for resistance to B. cinerea. The rst1 mutation thus defines a unique combination of disease responses to biotrophic and necrotrophic fungi in that it antagonizes salicylic acid-dependent defense and enhances JA-mediated defense through a mechanism that also controls cuticle synthesis.

We have purified and characterized a protein from the water-soluble fraction of wheat kernel (Triticum aestivum cv. S. Pastore) consisting of a single polypeptide chain blocked at its N-terminus by a pyroglutamate residue; the complete amino acid sequence has been determined by automated sequence analysis performed on peptide fragments obtained by enzymatic hydrolyses of the protein. Homology studies have shown that this protein is very similar (97% sequence identity) to the previously characterized wheatwin1 as well as to other members of the pathogenesis-related (PR) proteins of class 4; in analogy with wheatwin1, we have termed this protein wheatwin2. Both wheatwin1 and wheatwin2 have specific antifugal activity toward the wide-host-range pathogen Botrytis cinerea and the wheat-specific pathogenic fungi of wheat Fusarium culmorum and Fusarium graminearum of groups 1 and 2. On the basis of their structural and functional properties, wheatwin1 and wheatwin2 can be classified as members of the PR4 protein family; this represents the first report concerning the presence of this kind of protein in wheat.

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A trypsin inhibitor from wheat kernel (WTI) was found to have a strong antifungal activity against a number of pathogenic fungi and to inhibit fungal trypsin‐like activity. WTI inhibited in vitro spore germination and hyphal growth of pathogens, with protein concentration required for 50% growth inhibition (IC50) values ranging from 111.7 to above 500 μg/ml. As observed by electron microscopy, WTI determined morphological alterations represented by hyphal growth inhibition and branching. One of the fungal species tested, Botrytis cinerea produced a trypsin‐like protease, which was inhibited by the trypsin inhibitor. WTI, as well as other seed defence proteins, appear to be an important resistance factor in wheat kernels during rest and early germination when plants are particularly exposed to attack by potential soil‐borne pathogens.

The effect on ambient pH of Fusarium culmorum during its growth on mineral medium and in apoplastic fluids from infected wheat seedlings, and the effect on the production and activity of the enzymes pectin lyase (PNL) and polygalacturonase (PG), were investigated. Fungal development on a weakly buffered mineral medium in the pH range 5·0 -8·0, with pectin as the sole carbon source, led to pronounced alkalinization, reaching values above 8·0. The increase in ambient pH was accompanied by enhancement of total PNL activity. Pectin lyase secretion was detected at pH 5·0 as a single isoenzyme. An additional isoenzyme was apparent during the increase in medium pH. Polygalacturonase was detected as a single isoenzyme only during early growth on medium buffered at pH 5·0. At this stage, the initial medium pH of 5·0, corresponding to the optimum pH for PG activity, appeared to be the most suitable for the activation of early production of this enzyme. During growth in acidified yeast extract medium the fungus secreted ammonia and increased medium pH. Similarly, in apoplastic fluids from inoculated seedlings the concomitant ammonia accumulation and rise in pH were recorded. This trend was accompanied by an increase in PNL, which could therefore function at close to its optimal pH. The results suggest that during infection of wheat seedlings by F. culmorum , pH modulation can lead to PNL production and activity, thus promoting colonization of host tissue.