| Abstract |
The main aim of the present thesis was to study, under laboratory conditions, the induced mechanism(s) of resistance of French bean to F. solani f. sp. phaseoli (the causal pathogen of root and hypocotyl rot disease of beans). The normal (not induced) mechanisms of resistance of beans to this disease were also considered. Furthermore, the mechansims of disease resistance to bean anthracnose caused by C. lindemuthianum were also investigated for comparison.
The main methods of the study were:
1- Incubation of excised bean hypocotyls (of five different cultivars) by the droplet technique and incubation at 20 and 30 C.
2- Morphological observations of the host reactions for 30 days.
3- Observations of the histopathological interactions at the inoculation sites (the epidermal and outer cortical layers) of the most resistant and most susceptible interaction systems.
4- Analyses by thin layer chromatography of the extracts of the inoculated hypocotyls, 2, 4 and 7days after inoculation, and also the extracts of the uninoculated (control) hypocotyls.
5- Bioassays of the isolated compounds on the developed TLC plates for the detection of antifungal compounds.
6- The spectrophotometrical analysis of the detected phytoalexin(s) and the constitutive antifungal phenolic compound(s).
At 20 C, bean hypocotyls of cv. Contender showed susceptibility to infection by either of the used pathogens; whereas those of cv. Swiss Blanc were resistant, but hypocotyls of cvs. Giza 3, Giza 4 and Canadian Wonder showed different susceptibilities.
At 30 C, hypocotyls of cv. Contender, inoculated with F. solani f. sp. phaseoli, showed intermediate reaction tending towards susceptibility; whereas those of cvs. Swis Blanc, Giza 3, Giza 4 and Canadian Wonder, inoculated by the same pathogen, showed various degrees of resistance.
Hypocotyls of all bean cultivars, inoculated with C. lindemuthianum and incubated at 30 C, showed resistance reactions.
At 30 C, resistance to these two pathogens were induced, in general, in inoculated hypocotyls of all bean cultivars.
It can be concluded that the incubation of Fusarium- or Colletotrichum-inoculated bean hypocotyls at 30 C favours the induction of resistance of bean hypocotyl cells to these fungal pathogens. Resistance and induced resistance of bean hypocotyl cells were expressed by one (or more) of three mechanisms; namely, hypersensitivity, wall alterations or possibly phytoalexin accumulation. |
