Caracterização, patogenicidade de Exserohilum rostratum e mecanismos de defesas de plantas de arroz

Abstract

The pathogens are constantly undergoing changes, environmental and parasitic, this fact makes the need for knowledge of the interactions between organisms and agroecosystems. This study aimed to characterize morphological and molecular a new fungal species associated with rice cultivation, as well as, determine the pathogenicity, the damage caused grain when inoculated at flowering and plant defense responses through contact with the pathogen. Morphological identification was made based on the morphology of conidiophores, conidia, conidial germination, color, shape and septa. Molecular characterization was performed by extraction of fungal DNA subjected to PCR with primer pairs ITS4 primers ITS1, then the band containing the DNA fragment was excised and sent to the embodiment sequencing. The pathogenicity test was conducted with seedlings of BRS Pelota, PUITA INTA-CL e IRGA 424, inoculated with a spore solution adjusted to 2 x 104 conidia ml-1 . To determine the damage to grains were mounted parallel experiments in the greenhouse with the BRS Pelota, Puita INTA-CL and IRGA 424 inoculated at flowering in a randomized block design (RBD) with three replications and two factorial arrangement of type 3 x 2, where factor 1 corresponds BRS Pelota cultivar, Puita INTA-CL and IRGA 424, factor 2 corresponds to the presence and absence of inoculum, the variables analyzed were: incidence, quantification and location of the inoculum, index of disease and damage production components. For evaluation of the responses of rice plants inoculated with E. rostratum was collected plant tissue of the previous experiment plants and analyzed following a factorial scheme of type 3 x 2 x 5, where factor 1 corresponds BRS Pelota cultivar, Puita INTA- CL and IRGA 424, factor 2 corresponds to the presence and absence of inoculum and factor 3 times collection, the variables analyzed were: incubation period (IP), differentiated conidia in appressoria, number of necrotic cells (NCN), intensity Cell blackout, determining the concentration of total soluble phenolic compounds (CFSTs), lignin derivatives thioglycolic acid (DLAT) and activity of catalase (CAT) (EC 1.11.1.6), peroxidase (POX, EC 1.11.1.7) and polyphenol oxidase (PPO , EC 1.10.3.1). The conidiophores and conidia had an average length of 93 and 98 µm respectively, the average width of 9 conidia was 25 µm had obclavado, dark form, with the average for the presence of 8 septa and conidia germinate at both ends, The molecular characterization generated a product of approximately 600 pairs of nucleotides the completion of the sequencing and comparison to the database GenBank showed 99% similarity with the fungus Exserohilum rostratum. There was interaction between the cultivar factor and inoculum for th e production of components for the disease index, there was a significant difference for all cultivars when compared with their non-inoculated controls. On responses of rice plants to E. rostratum at flowering, there was triple interaction between factors. The fungal species present in rice cultivation in Rio Grande do Sul state is the E. rostratum, capable of causing damage to cultivars like BRS Pelota, Puita INTA-CL and IRGA 424, induce damage cellular necrosis and increase enzyme concentration and lignin.