Ecological adaptations influence the susceptibility of plants in the genus Zantedeschia to soft rot Pectobacterium spp.

Soft rot disease caused by Pectobacterium spp. is responsible for severe agricultural losses in potato, vegetables, and ornamentals. The genus Zantedeschia includes two botanical groups of tuberous ornamental flowers that are highly susceptible to the disease. Previous studies revealed that Z. aethiopica, a member of the section Zantedeschia, is significantly more resistant to Pectobacterium spp. than members of the same genus that belong to the section Aestivae. During early infection, we found different patterns of bacterial colonization on leaves of hosts belonging to the different sections. Similar patterns of bacterial colonization were observed on polydimethylsiloxane (PDMS) artificial inert replicas of leaf surfaces. The replicas confirmed the physical effect of leaf texture, in addition to a biochemical plant-bacterium interaction. The differential patterns may be associated with the greater roughness of the abaxial leaf surfaces of Aestivae group that have evolutionarily adapted to mountainous environments, as compared to Zantedeschia group species that have adapted to warm, marshy environments. Transverse leaf sections also revealed compact aerenchyma and reduced the total volume of leaf tissue air spaces in Aestivae members. Finally, an analysis of defense marker genes revealed differential expression patterns in response to infection, with significantly higher levels of lipoxygenase 2 (lox2) and phenylalanine ammonia lyase (pal) observed in the more resistant Z. aethiopica, suggesting greater activation of induced systemic resistance (ISR) mechanisms in this group. The use of Zantedeschia as a model plant sheds light on how natural ecological adaptations may underlay resistance to bacterial soft rot in cultivated agricultural environments.

Host Specificity and Differential Pathogenicity of Pectobacterium Strains from Dicot and Monocot Hosts.

Recent phylogenetic studies have transferred certain isolates from monocot plants previously included in the heterogeneous group of Pectobacteriumcarotovorum (Pc) to a species level termed Pectobacterium aroidearum. The specificity of Pectobacterium associated infections had received less attention, and may be of high scientific and economic importance. Here, we have characterized differential responses of Pectobacterium isolates from potato (WPP14) and calla lily (PC16) on two typical hosts: Brassica oleracea var. capitata (cabbage) a dicot host; and Zantedeschia aethiopica (calla lily) a monocot host. The results revealed clear host specific responses following infection with the two bacterial strains. This was demonstrated by differential production of volatile organic compounds (VOCs) and the expression of plant defense-related genes (pal, PR-1, lox2, ast). A related pattern was observed in bacterial responses to each of the host's extract, with differential expression of virulence-related determinants and genes associated with quorum-sensing and plant cell wall-degrading enzymes. The differences were associated with each strain's competence on its respective host.