Abstract
BackgroundMicroorganisms capable of utilizing vegetable tissues for multiplication in soil were isolated, cultivated in liquid medium prepared from the same vegetable tissues, and tested for ability to activate resistance in pepper leaves against Phytophthora blight caused by Phytophthora capsici.ResultsAmong the 121 microorganisms isolated, a fungus Humicola phialophoroides showed distinct ability to produce substances capable of activating resistance. The resistance-activating substances produced by H. phialophoroides were mostly retained in the mycelium, and were readily extracted from the mycelium powder with polar solvents. The extract was not inhibitory to zoospore germination or germ tube growth of P. capsici. In pepper leaves, the extract took only about 12 h to activate resistance against P. capsici. After activation, washing treated leaf surface with water did not have much effect on the resistance expression. In addition to being able to move from the upper leaf surface to lower leaf surface, the resistance-activating substances were capable of moving 5 mm acropetally and 10 mm basipetally in pepper leaves, Chromatography of the extract on silica gel column suggests that there are probably more than three components in the extract with resistance-activating ability. The resistance-activating activity of the mycelium extract was not affected by treatment with either cation or anion exchange resins, indicating that none of the active components have positive or negative charges on their molecules.ConclusionResults show that H. phialophoroides is capable of producing multiple resistance-activating substances which are mostly retained in the mycelium. The study also indicates that none of the active components have positive or negative charges on their molecules.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-55-40) contains supplementary material, which is available to authorized users.
Highlights
Microorganisms capable of utilizing vegetable tissues for multiplication in soil were isolated, cultivated in liquid medium prepared from the same vegetable tissues, and tested for ability to activate resistance in pepper leaves against Phytophthora blight caused by Phytophthora capsici
Activation of disease resistance by isolated microorganisms From the four soil samples, 38 bacteria, 26 actinomycetes and 57 fungi which were capable of utilizing vegetable tissues for multiplication in soil were isolated
Using the method developed in this study, 3 out of 121 isolates of microorganisms obtained from soils showed ability to produce substances capable of activating resistance in pepper leaves against infection by P. capsici
Summary
Microorganisms capable of utilizing vegetable tissues for multiplication in soil were isolated, cultivated in liquid medium prepared from the same vegetable tissues, and tested for ability to activate resistance in pepper leaves against Phytophthora blight caused by Phytophthora capsici. Phytophthora blight caused by Phytophthora capsici is a devastating disease of pepper (Capsicum annuum L.) and several other economically important crops (Hausbeck and Lamour, 2004 ; Hwang and Kim, 1995). A commonly recommended method for plant disease control is the use of resistant cultivars. Very few commercial pepper cultivars with strong resistance to P. capsici are available (Hausbeck and Lamour, 2004; Hwang and Kim, 1995). Resistance activation has emerged as an important alternative in the control of oomycete and fungal plant pathogens (Barbosa et al, 2008). Since soil contains abundant and diverse microorganisms (Alexander, 1997), it was hypothesized to be an ideal place to search for microorganisms capable of producing resistance-activating substances
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