Orobanche crenata resistance and avoidance in pea (Pisum spp.) operate at different developmental stages of the parasite

Orobanche crenata (broomrape) is an important constraint to pea (Pisum sativum) cultivation in the Mediterranean area, because little resistance is available in commercial crop varieties. Field experiments have demonstrated that some resistance is present in a number of P. sativum and P. fulvum accessions. The goal of this work was to characterize such resistance. The Pisum-O. crenata interaction and the resistance symptoms were studied under controlled conditions by using Petri dish and polyethylene bag assays. The content of phenolics and peroxidase activity in host tissue from infected and non-infected plants were also measured. Resistance and avoidance mechanisms, acting at different developmental stages of the parasite, have been identified, including low stimulation of O. crenata seed germination, unsuccessful penetration of host roots, delay in post-attachment tubercle development and necrosis of the attached tubercles. Infection caused an increase in the content of total soluble phenolics in some Pisum genotypes. Peroxidase activity was higher in resistant than in susceptible accessions. Results obtained with different Pisum genotypes showed that resistance is the result of several mechanisms acting at different stages of the infection process. Resistance is also related to increased levels of peroxidase activity in host roots.