Comparisons of Induced Pathogenesis-Related Proteins in Resistant and Susceptible Apple Cultivars in Response to Inoculation of the Pathogen Marssonia Coronaria

Abstract

Differential induction of the enzyme activity of seven pathogenesis-related proteins: chitinase (CHT), phenylalamine ammonia lyase (PAL), superoxide dismutase (SOD), polyphenol oxidase (PPO), peroxidase (POD), catalase (CAT) and malondialdehyde (MDA) from leaf extracts was characterized in both resistant 'Qinguan' and susceptible 'Fuji' apple cultivars at 0, 4, 8, 16, 24, 48, 72 and 96 h post-inoculation (hpi) with the pathogen Marssonina coronaria. Activity of all seven enzymes significantly increased in the resistant and the susceptible cultivars after inoculation with the pathogen ( P< 0.05). However, activity increment after inoculation (AIAI) was very different among the seven proteins, ranging from 52 to 173% in 'Qinguan' and 34 to 137% in 'Fuji'. AIAI of the seven enzymes in both cultivars had either one or two peaks at 16 hpi (CHT and PPO), 24 hpi (CAT, SOD, POD, PAL-'Fuji' and MDA), 48 hpi (PAL-'Qinguan' and CHT-'Fuji') or 72 hpi (CHT-'Qinguan'). Correlation analysis showed that expression of specific enzymes was significantly correlated ( P< 0.05) with the other enzymes studied within each apple cultivar. Results from a principal coordinate analysis showed that CHT, SOD, PAL and MDA were associated with one another in 'Qinguan', whereas PPO, POD, SOD and CAT were associated in 'Fuji'. A t-test showed that the AIAIs of all seven enzymes were significantly different between the two cultivars ( P< 0.05). The Mantel test showed that co-correlation coefficients of AIAI of the seven enzymes on the whole was non-significant between 'Qinguan' and 'Fuji' (R _xy= - 0.318, P= 0.060). Thus, both AIAI and the association pattern among pathogenesis-related proteins on the whole may be two important indicators that are contributing to resistance in apples in response to inoculation of M. coronaria. This study adds to our knowledge of apple responses to M. coronariaand provides information to potentially control this disease in the future.