Plant-parasites host resistance

A parasite must reproduce to complete its life cycle successfully. In this sense, the ability of an H. glycines individual to parasitize a soybean plant is measured by reproduction. In general, resistant hosts do not permit the female nematode to develop to reproductive maturity. Parasitism is a qualitative trait that the individual nematode either does or does not possess. In addition, nematode populations may be described quantitatively by their level of reproduction on a given host plant. Field populations of H. glycines... 

An epidemiological survey of complementary symptoms, reminiscent of the HR of terrestrial resistant plants, such as tip bleaching or accumulation of fluorescent aromatic compounds around the site of penetration of parasite propagules (Figs. 12.2 and 12.3), may facilitate the evaluation of the impact of host-microbe interactions in natural populations (Correa and Sanchez 1996 Ellertsdottir and Peters 1997 Bouarab et al. 2001a). This could allow one to test the importance of oxida-tive-burst-associated defense reactions in various biotic interactions. 

One or several of these mechanisms may be involved in resistance responses when lignification takes place in the plant cell walls. In the case of biotrophic parasites which rely on functional mature haustoria within living host cells for their development (33-36), lignification of the whole cell contents leading to rapid host cell death may in itself be a decisive factor in the expression of resistance. 

The term elicitor, initially defined as a fungal metabolite capable of inducing phytoalexin production when applied to host plants (122, 123), has since been applied to parasite-derived molecules which induce any facet of resistance in appropriate host plants, including lignification (124). 

Changed disposition of host plants to parasites and lowered resistance to abiotic stress — frost, heat, wind, e.g. 

Indirect effects of air pollution on vegetation result either from a general weakening or preconditioning of plants which make them a better host for pathogenes or parasites or reduce their resistance against frost und drought. Examples are reported. 

Volatile compounds emitted from the leaves and stems of agricultural crops during growth may affect plant host-parasite interactions that determine susceptibility or resistance to fungal infections and insect damage (7-9. ... 

Rishitin reaches two days after infection a concentration of about 100 g/g fresh weight of tuber tissue. This concentration is enough to delay hyphal growth of P. infestans in resistant tuber tissue. It leads one to think that rishitin may play some role in the defense reaction of potato tubers to infection by pathogen. Owing to growth retardant effect, rishitin may affect the parasite and host plant tissue. Further investigation is required to clarify the role of rishitin in the metabolism of both parasite and host and the host-parasite relationship. 

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