VIEW ARTICLE

Resistance

Differential Invasion by Tobamoviruses of Nicotiana megalosiphon Following the Hypersensitive Response. Michael Taliansky, Departamento de Patología Vegetal, Escuela Técnica Superior de Ingenieros Agrónomos, Ciudad Universitaria, Madrid 28040, Spain; Miguel A. Aranda, and Fernando García-Arenal. Departamento de Patología Vegetal, Escuela Técnica Superior de Ingenieros Agrónomos, Ciudad Universitaria, Madrid 28040, Spain. Phytopathology 84:812-815. Accepted for publication 24 April 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-812.

The tobamoviruses tobacco mild green mosaic virus (TMGMV) and tobacco mosaic virus (TMV) differ in their behavior in Nicotiana megalosiphon. Both viruses induce necrotic lesion formation in the inoculated leaves, but only TMV moves from the initially infected (necrotic) areas and is able to spread systemically, overcoming the hypersensitive response. The appearance and growth of necrotic local lesions induced by TMV or TMGMV in N. megalosiphon were shown to follow similar kinetics; however, virus accumulation in the local lesions was about five times greater for TMV than for TMGMV. In accordance with this, TMV replicated to much higher levels than TMGMV did in N. megalosiphon protoplasts. In N. tabacum 'Xanthi-nc,' a hypersensitive host for both viruses that was used as a control, no difference was observed in the kinetics of local lesion development nor in virus accumulation, either in local lesions or in protoplasts, for TMV or TMGMV. Thus, the ability of TMV, but not of TMGMV, to overcome the hypersensitive response of N. megalosiphon does not appear to be related to differences in the elicitation of the hypersensitive response but rather to the differential effect of a second resistance factor over the multiplication of TMGMV but not of TMV.