Variation in the life cycle and morphology of the tobacco host-race of Myzus persicae (Hemiptera: Aphididae) in relation to its geographical distribution.

Morphological variation and life cycle category were examined in 121 clones of Myzus persicae (Sulzer). The clones were collected from tobacco from three localities in Greece (Xanthi, Nea Efessos and Naphplion), one in Germany (Rheinstetten), one in France (Bergerac) and one in Spain (Madrid). Before morphometrics, all aphids were laboratory-reared on potato. The morphological variation was investigated using both canonical variates analysis and a novel non-parametric classification tree method. The life cycle category was examined by rearing the clones for three generations under short day conditions. In Nea Efessos a relative high proportion of clones was found to overwinter as eggs on the primary host. In the other regions all collected clones were non-holocyclic. Intermediate genotypes were found in all regions at percentages ranging from 4.0 to 24.0%. Androcyclic clones were found only in Xanthi, Greece (4.0%) and Rheinstetten, Germany (16.7%). The canonical variates analysis and the tree classification method revealed important intrapopulation polymorphisms in clones from Bergerac, Nea Efessos and Madrid. Both methods separated the populations originating from Greece from those collected elsewhere in western Europe. The observed morphological variation was probably due to genetic differences, since all clones were reared in a common environment. The results are discussed in relation to factors responsible for genetic divergence in M. persicae populations.

Pathogen-induced elicitin production in transgenic tobacco generates a hypersensitive response and nonspecific disease resistance.

The rapid and effective activation of disease resistance responses is essential for plant defense against pathogen attack. These responses are initiated when pathogen-derived molecules (elicitors) are recognized by the host. We have developed a strategy for creating novel disease resistance traits whereby transgenic plants respond to infection by a virulent pathogen with the production of an elicitor. To this end, we generated transgenic tobacco plants harboring a fusion between the pathogen-inducible tobacco hsr 203J gene promoter and a Phytophthora cryptogea gene encoding the highly active elicitor cryptogein. Under noninduced conditions, the transgene was silent, and no cryptogein could be detected in the transgenic plants. In contrast, infection by the virulent fungus P. parasitica var nicotianae stimulated cryptogein production that coincided with the fast induction of several defense genes at and around the infection sites. Induced elicitor production resulted in a localized necrosis that resembled a P. cryptogea-induced hypersensitive response and that restricted further growth of the pathogen. The transgenic plants displayed enhanced resistance to fungal pathogens that were unrelated to Phytophthora species, such as Thielaviopsis basicola, Erysiphe cichoracearum, and Botrytis cinerea. Thus, broad-spectrum disease resistance of a plant can be generated without the constitutive synthesis of a transgene product.