A histological and biochemical comparison of resistant and susceptible Populus genotypes inoculated with Sphaerulina musiva
N. ABRAHAM (1), P. Borowicz (2), J. Leboldus (3) (1) North Dakota State university, Plant pathology Dept #7660, U.S.A.; (2) North Dakota state university, U.S.A.; (3) Oregon state university, U.S.A.

Sphaerulina musiva, the causal agent of leaf spot and stem canker, is responsible for critical yield loss in Populus spp. However, the mode of leaf infection and the defense response of Populus spp. is still unclear. To understand the host-pathogen interaction, histological comparisons were performed between resistant and susceptible genotypes of hybrid poplar inoculated with S. musiva.  Leaf infection was examined at 48h, 96h, 1wk, 2wk, and 3wk post-inoculation (wpi) using scanning electron microscopy (SEM), fluorescent and confocal microscopy. SEM and laser scanning confocal microscopy coupled with aniline blue staining revealed similar results, with no major differences in pathogen growth and penetration of leaves between resistant and susceptible genotypes. Infection hyphae from germinated spores entered stomata and penetrated the cuticle directly. The host response was studied by examining the accumulation of hydrogen peroxide (H2O2) using fluorescent microscopy after DAB staining. No significant differences in percentage of dead tissue from H2O2 accumulation were observed between resistant and susceptible genotypes at 48h (p = 0.35), 96h (p = 0.44) and 1 wpi (p = 0.29). However at 2 wpi, there was a significant difference (p = 0.02) in H2O2 accumulation between genotypes. To further characterize the infection process of S. musiva on Populus spp., S. musiva is currently being transformed with red fluorescent protein through Agrobacterium tumefaciens mediated transformation

Abstract Number: P7-152
Session Type: Poster