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The role of methyl salicylate (MeSA) in the defense response of plants is investigated. MeSA is a major volatile compound produced by tobacco plants injected with tobacco mosaic virus. It is synthesized from salicylic acid. It may act as an airborne signal which activates disease resistance and the expression of genes related to defense in nearby plants and in the healthy tissues of the infected plant.

The spread of plant viruses at both cellular and whole-plant level can be studied using low-magnification lenses combined with confocal laser scanning microscopy (CLSM). The use of beta-glucuronidase (GUS), as a marker protein, enables the virus to be localized in specific tissues and cells, but this is a destructive process. The green fluorescent protein (GFP) from Aequorea victoria can be used to investigate the viral infection process, and the use of a potato virus X-based vector to express GFP is reported.

Plants with resistance evoke an incompatible interaction in the infected area to fight off viruses. Plants with transgenes with the same homology as the infecting virus can also resist infection by silencing the gene expression. A natural resistance of Kohlrabi (Brassica oleracea gongylodes) to the DNA pararetrovirus cauliflower mosaic virus, involving post-transcriptional gene silencing, is described.

The cloning of maize genes reveals the functioning of disease resistance genes of plants at molecular levels. The maize plant resists the fungal pathogen which infects the plant by degrading the fungal toxin. The plant resistance gene in the tomato is also cloned, which indicates the presence of gene-to-gene resistance. The tomato plant resistance gene identifies the pathogen's avirulence and produces the hypersensitive response. The response triggers the production anti-microbial compounds.

Studies on resistance development in North American arthroped pests prove that resistance does not depend on generation time but may depend on toxin concentration. Earlier analysis of Bacillus thuringiensis suggested that evolution of immunity depended on generation time and not on selection strength and other factors. Generation time affects resistance depending on the association between generation time and selection intensity of the generation.

American farmers are feeling the effects of a consumer movement against genetically modified (GM) foods which has spread across Europe and Japan. The farmers, while appreciating the convenience of the built-in pesticides in GM crops, fear they will not be able to find buyers for their harvests. The American Corn Growers Association has advised its members not to plant GM maize, while the Organic Trade Association is debating how best to protect its members' crops from 'genetic trespass'.

Some observers believe that extensive planting of corn and cotton which has been genetically engineered to produce a toxin made by the soil bacterium Bacillus thuringiensis (Bt) will place great genetic pressure on insects. This will in turn cause resistance to Bt toxin to emerge very quickly. Furthermore, they believe that resistance management plans are insufficient. They claim that if Bt cotton is to continue to be used, it will be necessary to increase refuges in order to ensure that sufficient numbers of non-resistant insects are present.