Host-Parasite Interaction During Development of Major Seed-Borne Fungal Diseases

Abstract

Host-parasite interaction using four major seed-borne fungal diseases of cereals as models – Fusarium head blight and blast for wheat, bakanae disease of rice, and Philippine downy mildew of maize – is described in this chapter. To establish a reliable method for wheat head blight disease rating, three isolates of Fusarium graminearum differing in aggressiveness on susceptible German spring wheat genotype ‘Munk’ were examined for their upward and downward infection of the floret. The low aggressive isolate was ahead of the symptoms above and below the point of inoculation. The moderately aggressive isolate caused less infection below the point of inoculation compared with the highly aggressive isolate. Latent infection was less frequent and white head symptoms were occasionally observed. High infection below and above the point of inoculation was exhibited by the highly aggressive isolate. There was strong negative correlation between head blight rating and grain weight (r = −83) and number of kernels (r = −94) using 26 isolates of F. graminearum. For the wheat-blast fungus interaction, infection of near isogenic isolate of Pyricularia oryzae on resistant and susceptible wheat and barley cultivars at seedling stage was observed at the cytological and ultrastructural level. Wheat cultivars St43 and ‘Norin 4’ (N4) and barley cultivar ‘Kwan’ (Bar19) were resistant to P. oryzae and showed hypersensitive response. Chromatin condensation was observed in St43 and Bar19 indicating an early phase of apoptotic cell response. Significant genotypic variation for aggressiveness of 40 Fusarium fujikuroi isolates causing bakanae disease on two rice varieties PSBRc18 and PSBRc54 was observed at seedling stage. The host-pathogen interaction of maize-Peronosclerospora philippinensis causing downy mildew of maize at the histopathological level is also discussed.