Histological Examination of Cold‐Induced Resistance to Yellow Rust in Winter Wheat

ABSTRACT

The mechanisms of cold‐induced resistance against yellow rust ( Puccinia striiformis f. sp. tritici ) were investigated in three varieties of winter wheat ( Triticum aestivum ; Anja, Elixer and Tonnage). Assessments of infection type score and histological staining of fungal structures, callose formation and plant cell death in infected wheat seedlings that had undergone prolonged cold treatment (vernalisation at 5°C for 8 weeks) or had been grown under normal conditions in a greenhouse were carried out to investigate cold‐induced resistance responses. Vernalisation led to a significant decrease in infection type scores on all varieties and a strong cold‐induced resistance response in Elixer and Tonnage. Histological analysis of fungal spore germination, substomatal vesicle formation at early infection stages (2–4 days after infection), fungal leaf colonisation and pustule formation at 11 days after inoculation (DAI) found that vernalisation led to a decrease in the number of germinated spores and leaf colonisation on all varieties, while the effect of vernalisation on substomatal vesicle formation and pustule development was variety dependent. Further histological analysis of callose deposition and hypersensitive responses (HR) in the leaves suggested that callose deposition was correlated with the infection level on the leaves and did not increase as a result of vernalisation. Plant cell death did not appear to play a significant role in the acquired cold‐induced resistance at early infection stages (2 and 4 DAI).