Ethylene, jasmonate, and salicylate play important roles in plant defense responses to pathogens. To investigate the contributions of these compounds in resistance of tomato (Lycopersicon esculentum) to the fungal pathogen Botrytis cinerea, three types of experiments were conducted: (a) quantitative disease assays with plants pretreated with ethylene, inhibitors of ethylene perception, or salicylate; (b) quantitative disease assays with mutants or transgenes affected in the production of or the response to either ethylene or jasmonate; and (c) expression analysis of defense-related genes before and after inoculation of plants with B. cinerea. Plants pretreated with ethylene showed a decreased susceptibility toward B. cinerea, whereas pretreatment with 1-methylcyclopropene, an inhibitor of ethylene perception, resulted in increased susceptibility. Ethylene pretreatment induced expression of several pathogenesis-related protein genes before B. cinerea infection. Proteinase inhibitor I expression was repressed by ethylene and induced by 1-methylcyclopropene. Ethylene also induced resistance in the mutant Never ripe. RNA analysis showed that Never ripe retained some ethylene sensitivity. The mutant Epinastic, constitutively activated in a subset of ethylene responses, and a transgenic line producing negligible ethylene were also tested. The results confirmed that ethylene responses are important for resistance of tomato to B. cinerea. The mutant Defenseless, impaired in jasmonate biosynthesis, showed increased susceptibility to B. cinerea. A transgenic line with reduced prosystemin expression showed similar susceptibility as Defenseless, whereas a prosystemin-overexpressing transgene was highly resistant. Ethylene and wound signaling acted independently on resistance. Salicylate and ethylene acted synergistically on defense gene expression, but antagonistically on resistance.In nature, plants have to cope with abiotic and biotic stresses. Mechanisms have evolved that enable plants to resist drought and wounding but also attack by pathogenic microorganisms. Such mechanisms have been the subject of study for many years and recent results indicated striking similarities between biotic stress on the one hand, and senescence (Quirino et al., 2000), wounding (Romeis et al., 1999), and aging and drought stress (Langenkamper et al., 2001) on the other hand. The plant hormone ethylene is an important signal in many of such abiotic stress situations but also in plant-pathogen interactions (Boller, 1991; Bleecker and Kende, 2000). Production of ethylene can be induced by pathogen invasion, by fungal toxins as well as by race-specific and endogenous elicitors. Ethylene may activate plant defenserelated processes such as the production of phytoalexins (Fan et al., 2000), pathogenesis-related (PR) proteins (Rodrigo et al., 1993; Tornero et al., 1994 Tornero et al., , 1997 van Kan et al., 1995), the induction of the phenylpropanoid pathway (Chappell et al., 1984), and cell wall alterations (Bell, 1981). Therefore, ethylene has...

Pepper fruits, of Capsicum annuum cv. Padron, undergo changes in content of capsaicinoids, lignin, and free phenolics during the maturation process. Although capsaicinoids increase with development, the maximal levels of free phenolics and lignin are observed during the early stages of development. A decrease of peroxidase activity was observed during maturation, and this was related with a decrease in other physiological parameters studied, namely chlorophylls and pH. Subcellular fractionation studies reveal that most peroxidase activity is localized in the soluble fraction throughout development. The changes in the peroxidase activity were accompanied by changes in the different isoenzymes. Acidic isoenzymes increased whereas the basic isoenzymes decreased over the same period, and the changes in these isoenzymes were related with capsaicin metabolism.

Pepper (cv. Padrón) shows a spatial gradient in the content of phenolic compounds, and particularly of capsaicinoids, along the stem. These compounds were consistently more abundant in apical fruits than in fruits belonging to middle and basal segments. Analysis of the two principal capsaicinoids in fruits showed that the proportion of capsaicin was always higher than that of dihydrocapsaicin. Capsaicinoids were also found to be present in vegetative organs, such as stem and leaves. In this case, the proportion of individual capsaicinoids was different than that in fruits, and dihydrocapsaicin was found to be more abundant. To find out whether the capsaicinoids in vegetative organs came from the fruits, the floral buds were removed and fruit formation was prevented. Capsaicinoids were not detected in the stem and leaves of floral bud-deprived plants, suggesting that they did originate from the fruit.

The application of the nonpathogenic isolate Fusarium oxysporum 47 (Fo47) reduced the symptoms of verticillium wilt, phytophthora root rot and phytophthora blight in pepper plants. Botrytis cinerea was also tested on the leaves of plants treated with Fo47, but no protection was observed. Verticillium dahliae colonies cultured in the presence of Fo47 grew slower than control cultures, but Phytophthora capsici growth was unaffected by Fo47. At least part of the protection effect observed against V. dahliae could therefore be due to antagonism or competition. In order to search for induced resistance mechanisms, three defence genes previously related to pepper resistance were monitored over time. These genes encode a basic PR-1 protein (CABPR1), a class II chitinase (CACHI2) and a sesquiterpene cyclase (CASC1) involved in the synthesis of capsidiol, a phytoalexin. These three genes were transiently up-regulated in the roots by Fo47 in the absence of inoculation with the pathogen, but in the stem only CABPR1 was up-regulated. In plants that were inoculated with V. dahliae after the Fo47 treatment, the three genes had a higher relative expression level than the control in both the roots and the stem.

Phytophthora crown rot, caused by Phytophthora capsici, is potentially the most destructive disease of pepper in Spain. Phenotypic and genetic diversity of 16 P. capsici isolates collected from 11 farms in northwest Spain was characterized based on virulence, mating type, sensitivity to metalaxyl, and genetic analysis using random amplified polymorphic DNA (RAPD) methods. Low variability was observed among the isolates in their metalaxyl response, with 87.5% being highly sensitive. No isolates of the A2 mating type were detected. More variability was found in the virulence assay, and isolates were classified into two groups according to their pathogenicity on a set of four pepper cultivar differentials. Genetic variation examined with eight RAPD primers generated 92 polymorphic bands and revealed the existence of different patterns among isolates. Cluster analysis using the unweighted pair-group method with arithmetic averages (UPGMA) separated the Spanish isolates into three RAPD groups and established a relationship between the Spanish population and a representative worldwide group of isolates. No correlation was found between groups obtained by RAPD analysis and groups defined by virulence or metalaxyl response.

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