Resistance-related gene transcription and antioxidant enzyme activity in Nicotiana spp. resistant to anthracnose

The two tobacco relatives of Nicotiana alata and Nicotiana longiflora display a high level of resistance against Colletotrichum nicotianae and the two genes NTF6 and NtPAL related to pathogen defense transcription were higher in N. alata and N. longiflora than the commercial cv. K326. Inoculation with C. nicotianae reduced the abundance of NTF6 and NtPAL transcript during the first 48 h post inoculation (hpi) when only biotrophic hyphae were present, but increased it over the following 24 h as necrotrophic hyphae began to predominate. Activity levels of phenylalanine ammonia lyase, peroxidase and polyphenol oxidase changed markedly at 72 hpi. The conclusion was that the pathogen enters the host leaf within 24 hpi, triggering the up-regulation of various defense-related genes in a resistant host plant. By 72 hpi, the pathogen switched to necrotrophic growth to avoid contact with the increasing presence of host defense compounds.Key words: Nicotiana alata, Nicotiana longiflora, tobacco anthracnose resistance-related gene, antioxidant enzyme activity