Studies On The Interactions Between Geranium Carolinianum L. And Its Pathogenic Fungus Plasmopara Geranii-caroliniani Schr(?)ter

In nature populations, interactions between host plants and their pathogens have been deeply studies. The occurrence and expression of disease caused by fungi in plants is reference greatly to their habitats, environmental factors (both biotic and abiotic factors) in which may affect not only host or pathogen individuals but also their mutual interactions. In western ,environmental modification of host – pathogen interactions is always an emphasis in plant population ecological.In this paper , host Geranium carolinianum L. is a common herbaceous plant in nature, pathogen Plasmopara geranii-caroliniani Schr?ter is a parasitic fungus on it .In the long-term interactions with its pathogen, host plant Geranium carolinianum L. have evolved two genotypes: resistant type and susceptible type. Field investigations found that the host population structure had reference to its habitat. The same to the proportion between two genotypes and their ecological characteristics .We give these two genotype individuals of host Geranium carolinianum L. different light intensity and two level interspecific competitions respectively in order to analyze the influences on their livability, nutrition growth and reproduce outputs with its pathogen P. geranii-caroliniani Schr?ter exists. The results show that: (1) Pathogen P. geranii-caroliniani Schr?ter cause great damage to host's physiology process by affect its leaves. The chlorophyll content of infected leave is only 32% of healthy one. Studies on MDA content and electric conductivity indicates that the leave structure is destroyed seriously also. Proper shading may stimulate host's physiology adaptation, the leave's chlorophyll especial chlorophyll b content are higher than that under normal sunlight. It is useful to improving leave's efficiency in light absorbing.(2) Variation in light intensity may influence the host –pathogen interactions distinctly. To resistant hosts, the death rates revealed no difference between two experiments sets, while they are different to susceptible ones. Meanwhile, the death rates have difference between two genotypes in treatment set under the pathogen pressure, concerning the sunlight set, there is no difference. But the hosts express differently in nutrition growth with different genotypes and two-level light intensity .The same genotype hosts between two experiment sets are differ greatly in reproduce output. At the same time, there is no difference between two genotypes in sunlight set, while in treatment set , susceptible hosts' reproduce output is 53% of resistance ones'. (3) In plant communities, different interspecific competition may not bring alike influence on the host –pathogen interactions. In high interspecific competition pattern, pathogen will make 50% susceptible hosts dead while no use to resistant hosts. There is no difference between two genotypes in nutrition growth, but the reproduce output of resistant ones will superior to others. Oppositely in low interspecific competition habitat, there is no difference in reproduce while differently in nutrition growth between two genotypes. No matter of its genotype, host growth in low interspecific competition pattern will be better than that in high interspecific competition habitat.(4) In host—pathogen interactions, pathogen may change hosts population size and structure by influence their livability, while the effect on host reproduce will influence new generation's population size and the proportion of two genotypes individuals. But it must be pointed out that all of those are relevant greatly to the conditions of light intensity or inerspecific competition pattern in their habitats.