The gene-for-gene relationship between Capsicum annuum L. and tobacco mosaic virus: effects on virus multiplication, ethylene synthesis and accumulation of pathogenesis-related proteins

Abstract

Pepper ( Capsicum annuum) plants containing the L 1 or L 3 genes for resistance to tobacco mosaic virus, and susceptible hosts (L +), were inoculated with TMV strains overcoming neither, one or both of the resistance genes. Diverse symptoms were produced in the different host-virus combinations. Measurements of virus multiplication confirmed, in quantitative terms, the operation of a gene-for-gene relationship between host resistance and virulence in the virus. Host metabolism was studied during different types of host-virus interaction. Accumulation of pathogenesis-related (PR) proteins was examined on native and denaturing gels. Major PR proteins with molecular masses of 11, 18, 21 and 28 kD were found, together with several other bands: all were trypsin-resistant. One host protein disappeared after certain types of infection. PR proteins were induced mainly in necrotically-infected inoculated leaves, and in necrotic or non-necrotic, systemically-infected leaves. TMV strain SL, which caused no necrosis on any host, was an efficient inducer of PR proteins. Little evidence was found for any acquired systemic resistance in the host-virus combinations tested. The relationships between ethylene synthesis and necrosis and PR protein accumulation were examined. Necrotic infections stimulated ethylene synthesis, but symptomless inoculated leaves with enhanced ethylene production were also found. The non-necrotic strain SL did not significantly enhance ethylene production. Cases were found where ethylene was increased without PR protein accumulation, and conversely, where PR proteins increased without major ethylene increase.