Pattern-triggered immunity in blue and white seed cultivars of Papaver somniferum

Papaver somniferum (poppy) is a traditional component of Central and Eastern European cuisine and an important oilseed crop in the region. The crucial thread for poppy stable yield is pathogen infection. Thus, we need to understand poppy defence mechanisms in detail. The first robust layer of plant immunity, which plays a crucial role in combat against pathogens, is pattern-triggered immunity (PTI). Here, we provide the first insights into PTI in poppy. We selected four poppy varieties used in the food industry. We investigated poppy response to various peptide elicitors acting as microbe-associated molecular patterns (MAMPs) and damage-associated molecular patterns (DAMPs). Flg22 induced the most robust reactive oxygen species (ROS) burst among all tested peptides. Flg22 also triggered putative mitogen-activated protein kinase (MAPK) phosphorylation and seedling growth inhibition in all tested cultivars. We identified PsWRKY22 and PsPR2 as candidate marker genes suitable for monitoring poppy PTI responses. The tested poppy cultivars have low levels of salicylic acid. Callose accumulation was triggered by wounding but not by flg22. For studying PTI in poppy, wounding is a challenge that needs to be considered as it can obscure potential PTI responses. Our findings highlight conserved aspects of poppy immunity and challenges in studying poppy PTI. The established pipeline facilitates improving our understanding of poppy immunity and has the potential for widespread application in poppy breeding and improving selection for broad-spectrum disease resistance provided by enhanced PTI.