INDUCED SYSTEMIC RESISTANCE AGAINST THE PHYTOPATOGEN SCLEROTIUM ROLFSII IN PEANUT PLANTS INOCULATED WITH THE SYMBIONT BRADYRHIZOBIUM (ARACHIS) SP. SEMIA6144 AND THE BIOCONTROL AGENT BACILLUS SP. CHEP5

FIGUEREDO, SOLEDAD; TONELLI, MERÍA LAURA; VALETTI, LUCIO; FABRA, ADRIANA

Mar del Plata

Congreso; VIII Congreso de Microbiología general; 2012

Interaction of some plant growth promoting bacteria with plants can result in systemic resistance to pathogenic microbes. This phenomenon is called Induced Systemic Resistance (ISR). Compounds associated to ISR and biochemical alterations characteristic of ISR?expressing plants becomes obvious only in response to a pathogen infection. This defense state has been described as ?priming? and results in a more rapidly or more strongly response than during a primary infection. The enhanced plant?s defense is correlated with physical and chemical changes catalyzed by the phenylalanine ammonia lyase (PAL) enzyme. Previous studies in our laboratory demonstrated that the native isolate Bacillus sp. CHEP5 induced in peanut systemic resistance against the pathogen S. rolfsii (Tonelli et al., 2011). The aim of this work was to evaluate whether the presence of the peanut symbiont Bradyrhizobium sp. SEMIA 6144 affect the Bacillus sp CHEP5 ability to induce systemic resistance against S. rolfsii in this legume. Root system of 15 days old plants growing in pots with quartz sand was separated using the split method described by Fuchs et al.(1997). Each root part was put in glass tubes containing semi-solid Hoagland medium (0.6%) and one of the root parts was inoculated with one or both bacterial strains (Bradyrhizobium sp SEMIA6144, Bacillus sp. CHEP5). A week later, the other root part was challenged with the pathogen. After 24 h PAL activity was measured in leaves following Paynet et al. (1971) method. At 30 days post-pathogen challenge, disease symptoms were recorded and plants were harvested to determine their shoot and root dry weights, and chlorophyll content (Arnon, 1949). At this time, PAL activity was also evaluated in leaves from these plants. At 24 h post-pathogen challenge, PAL specific activity was significantly increased in plants inoculated only with Bacillus sp. CHEP5 or co-inoculated with Bradyrhizobium sp. SEMIA 6144, compared with plant without bacterial inoculation. At 30 days post-pathogen challenge, the shoot and root dry weights, chlorophyll content and PAL activity were higher in plants inoculated with one or both bacteria than in those only pathogen challenged. At this time PAL activity was higher than at 24 hs. By contrast, there was no difference between PAL activity in plants inoculated only with Bradyrhizobium sp. SEMIA 6144 after pathogen challenge and those treated only with S. rolsii. Considering results obtained, we concluded that the ability of Bacillus sp. CHEP5 to induce systemic resistance against S. rolfsii in peanut was not affected by Bradyrhizobium sp. SEMIA 6144. Furthermore, there is a correlation between PAL activity levels and the plant defense induced by Bacillus sp. CHEP5, and it seems that induction of PAL activity is an early step in the ISR signaling pathway that increases over the time.