<i>EFFECT OF SUBSTRATE AND TEMPERATURE ON THE BIOLOGICAL CONTROL OF PHYTOPHTHORA CAPSICI IN PEPPER (CAPSICUM ANNUUM L.)</i>
Abstract
The objective of this study was to compare the in vitro and in vivo effect of temperature and pH on the antagonistic capacity of the fungus Trichoderma harzianum, bacteria Burkholderia cepacia and Streptomyces rochei Ziyani on the wilt caused by Phytophthora capsici in pepper plants grown from seeds treated with each antagonist. In the in vitro assays, the interactions and antagonistic capacities of each antagonist against the pathogen P. capsici at 23 and 30ºC were analysed macroscopically and given a value of 4 on a scale of 0 (no superficial invasion of the P. capsici colony) to 4 (total superficial invasion and sporulating of the P. capsici colony). The optimal temperature was 30ºC for he bacteria St. rochei Ziyani and B. cepacia, and 25ºC for T. harzianum. A pH of 4.5 did not affect the inhibitory action of either bacteria, and even favoured it, but reduced the density and colour of T. harzianum colony without affecting its antagonistic capacity. In vivo experiments were carried out at 23ºC in a culture chamber because the aggressiveness and velocity of the necrosis reaction in infected stems is greater than at 30ºC.. The effect of pH on platelet growth was studied in vivo at pH values of 5.44, 4.95, 4.58, 4.20 and 3.48 in mixtures of peat, sand and 1M KCl in different proportions. In greenhouse conditions, the intensity of inhibition varied with the pH of the culture medium and of the antagonists. The effective reduction of the disease was 3.25 with the fungus T. harzianum, 2.10 with the bacteria B. cepacia and 1.85 with the bacteria St. rochei Ziyani, which represent reductions of 37%, 42% and 65% respectively. Control was in the peat, sand and 1M KCl mixtures at 25 2ºC and pH 4.8. The different concentrations of bacteria used did not give rise to different degrees of reduction in wilt. The defensive response of the plant is also favoured the C. annuum-P. capsici interaction at a structural level was studied by transmission electronic microscopyDownloads
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