The ability of Trichoderma harzianum to control the rotting of pepper (Capsicum annuum) plant roots caused by Phytophthora capsici was studied. Interactions between the fungi were assessed in vitro on three culture media (V8c, Czapek and 2% water agar) and in vivo in plants grown in a substrate inoculated with P. capsici and T. harzianum. Studies on mutual antagonism in vitro showed that P. capsici was inhibited by T. harzianum; however, the intensity of inhibition differed according to the medium used, being greatest on Czapek. Analysis of the fungal populations in the plant growth substrate showed that T. harzianum consistently reduced that of P. capsici over time. This reduction in the pathogen population was associated with a reduction in root rot of between 24 and 76%, although plant growth (dry weight) was still reduced by 21·2-24·7%, compared with the uninoculated control. In the absence of T. harzianum with the same pathogen inoculum levels, the reduction in dry weight was 59·8-68·6%, suggesting that T. harzianum reduced the damage.

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The soluble phenolic acids of the stems of three Capsicum annuum cultivars associated with differing resistance to Phytophthora capsici showed qualitative and quantitative variation after inoculation, notably an increase in the total phenolic acid content in the resistant and intermediate varieties. The soluble phenolic acids also retarded myeelial growth of P. capsici in culture. The most pronounced inhibitory effect was produced by f‐cinnamic acid, followed by p‐hydroxybenzoic, vanillic and salicylic acids. Colonization and necrosis spread throughout the stem of the susceptible cultivar whereas the stem of the resistant cultivar was only partially invaded. In the latter, invasion of the tissue adjacent to necrosis occurred in only 20% of the plants.

Egea. C, Alcazar, M, D. and Candela. M. E. 1996. Capsidioi; Its role in the resistance of Capsicum annuum to Phytophthora capsici. Plant. 98;[737][738][739][740][741][742] Inoculation ofthe stems of three Capsicum annuum h. cultivars showing different degrees of sensitivity to the fungal pathogen Phytophthora capsici, resulted in a hypersensitive reaction being expressed along the stems,. One of the peppers (cv. Smith-5) showed resistance by total inhibition of fungal growth. Capsidiol, a ph>1oalexin, which accumulates in tbe area of necrosis appears to be involved in this resistance. Capsidiol accumulation was analyzed by gas chromatograpby and was correlated with the restricted growth of P. capsici, in vivo and in vitro, confirming the former's fnngistatic and fungitoxic properties. The capacity to inhibit pathogenic growth was evident only wben capsidiol production exceeded i 204 ^g mT', a level reached in the resistant variety after 6 days of incubation. Experiments on induced resistance showed that a second inoculation of the stems of the three cultivars also resulted in necrosis and in an accumulation of capsidio), although to a lesser extent than in the first inoculation. The greater accumulation of capsidiol in the stems of cv. Smith-5 is in accordance with tbe resistance shown hy this cultivar to P. capsici, and confirms the implication of capsidioi in the disease resistance of this cultivar to fungal pathogens. Capsidiol has a fungistatic character at a mean concentration of 3.75 m.W, and is funsritoxic at levels above 5 mM. This level must be exceeded and all the growing h\pbae must be affected for capsidiol to qualify from being fungistatic to being fungitoxic.

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