natural-products-in-plant-pest-management

256 M. Santos et al.does not reflect the effect on the density of the mycelium, which can only beobserved under a microscope with a clear inhibition by the compost extracts,although this cannot be expressed in the graph.The sterilization of compost water extracts annuls the suppressing effecton fungal growth shown by non-thermally treated extracts, except forVerticillium dahliae and V. fungicola, for which inhibition values reach 60%,in compost tea incubated for 1 day at concentration levels of 10 and 15%.The detection of siderophores on GMC tea, which can affect the developmentof the fungal mycelium, occurred equally in the extract obtained simplyby filtering (F), in those that were microfiltered (C ) and in those that weresterilized (E), with the addition of FeCl 3to the medium. In these, the biologicalcomponent has not been eliminated, so besides the potential inhibitionthat siderophores can cause, we must bear in mind other antagonistic effectssuch as competition for nutrients, space, and so on.These results suggest that the microorganisms present in GMC producesiderophores, which grow outside the cells and kidnap iron, stopping itsavailability, thus preventing the in vitro development of the phytopathogensstudied.This study confirms the in vitro inhibition of the growth of eight pathogensand one mycopathogen, as well as the important role of siderophores inthis suppression. In our previous studies, the inhibiting power of GMC hadbeen verified against the nine fungi tested. As can be expected, the suppressivenessshown by GMC extracts is a combination of various factors, such ascompetition for nutrients, antibiosis, and production of lytic enzymes outsidethe cells and of low molecular weight molecules that are capable ofdegrading the fungus wall.The difference between the use of soil-applied composts and waterycompost extracts perhaps is best summarized as that the teas give immediatebut very short-term control of surface-spreading pathogens, while soil compostacts more slowly over a longer period of time and requires much largeramounts (York and Brinton, 1996).12.5 ConclusionDiseases that have been shown to be effectively suppressed by compost useinclude those caused by Fusarium, Phytophthora, Pythium and R. solani. Severalreports suggest that compost and compost-amended soil may alter theresistance of plants to disease. The microbes in compost teas can suppressdiseases in several ways: induced resistance, antibiosis and competition, anddirect destruction of pathogens structures. The effect is due to the activity ofspecific biocontrol agents in the batches of compost that suppress the disease.There are several reports on the control of plant pathogens or plant diseaseswith organic teas including airborne and soilborne diseases. GMC and itswater extracts have been reported to suppress fungal diseases. Compost canprovide natural biological control of diseases of roots as well as the foliage ofplants. Its water extracts (compost tea) have been proposed as substitutes for