Fotomorfogênese e Patogenicidade de Bipolaris bicolor em trigo, milho e sorgo

Abstract

The pathogen Bipolaris bicolor is of great importance in the production cycle of several agricultural crops, causing great losses in productivity. In order to build epidemiological models of populations of a pathogen, it is necessary to study its pathogenic variability and physiological responses to stimuli from physical factors, as it is of crucial importance in its management. In this context, the objective was to carry out the physiological characterization and verify the pathogenicity of six strains of B. bicolor. The physiological evaluation consisted of evaluating the influence of light on conidial germination. For this purpose, a suspension with a concentration of 1.6 x 105 conidia/mL of conidia from the six strains of B. bicolor were inoculated into Petri dishes containing agar-water medium and incubated in two light regimes: constant dark and light, in a completely (DIC) in a 6x2 factorial arrangement, with six strains of B. bicolor and two physical regimens with five replications. The length of the conidia germ tube was evaluated for 5 h. Additionally, for the characterization of the pathosystem and its physiology, the evaluation of the severity of the symptoms caused by the six strains in wheat leaves that were inoculated through mycelium discs and submitted to the BOD chamber under five photoperiods (12, 14, 16, 18 and 20 h of light) for six days, in DIC in a 6x5 factorial arrangement, with six strains of B. bicolor and five photoperiods, in five replications. At the same time, the pathogenicity and severity of the disease were evaluated in maize and sorghum leaves through the inoculation of mycelial discs and incubation for six days in a BOD chamber. To assess severity, the injured leaf diameter was measured daily and subsequently the Injured Leaf Area (AFL) was calculated. The results showed that there was an influence of the light regimes on the germination of the conidia of B. bicolor, being the constant dark regime the one that presented the longest average length of the germ tube. Regarding pathogenicity, when inoculated on wheat leaves, all isolates were pathogenic and differed in terms of symptom severity. The F-24-02 strain showed the highest disease severity index in all photoperiods. Regarding the luminosity factor, its influence on the pathosystem of B. bicolor was verified, with a reduction of the AFL with the increase of the daily time of exposure to light. The 14 h light photoperiod showed the greatest significant reduction in disease severity, with a tendency to stabilize with increasing hours of light exposure. Regarding the ability to infect other hosts, pathogenicity evaluations showed pathogenic capacity of all isolates evaluated in maize and sorghum leaves, with considerable levels of severity. However, it is noteworthy that low severity and presence of hypersensitivity reactions were noted in sorghum leaves.