Grandpa's biology - 09









HOST-PARASITE RELATIONS

The plant represents the environment in which fungus and virus develope
- an environment which will be affected by the two parasites
- an environment which will affect in return
the parasites behaviour




The host-parasite relations observed between the plant and the fusarium on the one hand and the plant and tobacco mosaic virus on the other still has to be explained, the conjunction of these phenomena theoretically providing an understanding of what happened in the case of the plant inoculated with both parasites.

If you look at diagrams on cell function, it can be considered that a plant is in good health if its physiological activity is normal and that it is sick if this same activity deviates from normal for various reasons:

- reasons linked to the nature of certain genes in the event of genetic diseases,
- reasons linked to the type of environment in the event of physiological diseases,
- reasons linked to the presence of a pathogenic agent (animal, bacterium, fungus, virus) in the event of infectious diseases.

It is the third type of disease which interests us, the approach preferred by Papy, in this case based on the following idea: the plant represents the environment in which the fungus and the virus developed:
- an environment which evolves, this evolution being altered by appropriate hormone treatments;
- an environment, the evolution of which will be affected by the two parasites.
- an environment, the evolution of wich will also affect the two parasites


This led to the following two facets of the studies:
- the influence exerted by the parasite on the plant-host, particularly on the evolution of sugar and nitrogen concentrations in the leaves and roots during experiments, depending on IAA and GA treatments of course, and in relation with the data provided by the literature on the hormonal imbalance of diseased tissues;
- the influence exerted by the plant-host, in other words the influence of the environment in which the fungus and virus develop, on the evolution of the two parasites.


One more remark: according to the literature available at the end of the 1960's:
- fusariosis was thought to cause hyperauxinia in leaves and hypoauxinia in roots. In view of the results obtained from plants free of disease (chap. 8), it should therefore slow the evolution of the sugar/nitrogen ratio in diseased plants;
- the tobacco mosaic virus was thought to cause hypoauxinia in leaves. It should therefore accelerate the physiological evolution of these organs;
- no information on what happens to roots in this case could be found, nor on gibberellin concentration in diseased tissues, whether infected by the virus.



presentation/contentsa work of popularizationstory of modern biologythe point of view of French citizenssome basic concepts to recallgrandpa's hypothesishow to verify this hypothesisfirst testsevolution of plants according to auxin and gibberellin treatmentshost-parasite relationsaction of the fungus on the plantaction in return of the plant on the fungusaction of the virus on the plantaction in return of the plant on the virusa plant subjected to double attack by both fungus and virusthe scientific debatethe Peter principleconclusion - answer to some questionsimages




Grandpa's biology - 09