Plant hosts

Insect and plant pathogen attacks are reduced because 1) natural enemies of the pests are increased in the polyculture ecosystem because the array of hosts for the natural enemies is increased, 2) and the movement of pests from one host plant to another is interrupted by the presence of a different host plant growing nearby (36). In this way overall pest damage is substantially reduced. 

Most biological and cultural pest controls return greater profits than pesticides. For example, biological pest controls are reported to return from 30 to 300 per dollar invested in control (16). Various cultural controls like host plant resistance, crop rotations, and tillage, also return 30 to 300 per dollar Invested in pest control (16). 

Fig. 1. Infection and transformation of a suitable host plant by Agrobacterium tumefaciens (from Bryant, 1988).

Fig. 2. Schematic representation of the Ti-plasmid of Agrobacterium, showing the genes involved in transformation of host plants. Note that the genetic map is not to scale in reality, the T-region makes up about 10% of the total plasmid genome (from Bryant, 1988).

Additional information relating to cyanogenesis polymorphisms can be found in a recent paper by Schappert and Shore (1999) who stndied the phenomenon in Turnera ulmifolia L. (Tnmeraceae), which is used by Euptoieta hegesia (Lepidoptera Nym-phalidae) as its primary host plant. 

Oaks and especially Quercus coccifera are host plants for Kermes ilicis, producing the red kermes pigment. In Asia, the Laccifer lacca insects that grow on trees like Schleichera oleosa, Ziziphus mauritiana, and Butea monsperma are the sources of the red lac dye. - ... 

Patten CL, BR Glick (2002) Role of Pseudomonas putida indoleacetic acid in development of the host plant root system. Appl Environ Microbiol 68 3795-3801. 

Chapters 7 and 9 discuss specific exchange of molecular signals (the so-called molecular cross talk ) between beneficial microorganisms, such as rhizo-bia and mycorrhizas, and their host plants. Molecular cross talk seems to be a prerequisite mechanism for most of the plant infection by soil microorganisms (14). Only for a few microbial infections, however, the sequence and type of molecular signals involved have been characterized. Thus, there is the need for further studies to elucidate the unknown molecular cross talk between the most common rhizobacteria and fungi and the plant roots it is also needed to better understand how molecular cross talk responds to the changing environmental conditions. The potential applications of these studies are important because the... 

This suggests that it may be possible to manipulate the rhizosphere flora through genetic changes in the host plant. Of particular interest is whether different varieties, by exuding different compounds, can influence the rhizosphere flora in a way that would benefit the plant. 

P. Bonfante and S. Perotto, Strategies of arbuscular mycorrhizal fungi when infecting host plants. New Phytologist 130 3 (1995). 

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