Orobanche crenata resistance and avoidance in pea (Pisum spp.) operate at different developmental stages of the parasite A PE ´ REZ-DE-LUQUE*, J JORRI ´ N  , J I CUBERO à & D RUBIALES* *CSIC-Instituto de Agricultura Sostenible, Co ´rdoba,  Dep. Bioquı´mica y Biologı´a Molecular,ETSIAM-UCO, Co ´rdoba, and àDep. Gene´tica, ETSIAM-UCO, Co ´rdoba, Spain Received 22 September 2004 Revised version accepted 14 March 2005 Summary Orobanche crenata (broomrape) is an important con- straint to pea (Pisum sativum) cultivation in the Medi- terranean area, because little resistance is available in commercial crop varieties. Field experiments have demon- strated 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 develop- mental stages of the parasite, have been identified, including low stimulation of O. crenata seed germina- tion, 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. Keywords: Orobanche crenata, Pisum sativum, Pisum fulvum, broomrape, pea, peroxidase activity, phenolics, resistance. PE ´ REZ-DE-LUQUE A, JORRI ´ N J, CUBERO JI & RUBIALES D (2005) Orobanche crenata resistance and avoidance in pea (Pisum spp.) operate at different developmental stages of the parasite. Weed Research, 45, 379–387. Introduction Crenate broomrape (Orobanche crenata Forsk.) has been known to attack legumes since the times of Ancient Greece (Cubero, 1994). Orobanche infection in pea (Pisum sativum L.) fields can lead to yield losses up to 80% (Rubiales et al., 1999, 2003a, 2005) and result in the abandonment of pea cultivation in infested areas. This highlights the need for a control strategy, in which host-plant resistance could play a major role. Resistance to O. crenata in legumes such as faba bean (Vicia faba L.) and pea has proven to be a multigenic character with very low heritability, making breeding for Orobanche resistance a difficult task (Cubero, 1994; Rubiales, 2003). The quantitative resistance resulting from a very arduous selection allowed the release of faba bean cultivars with useful levels of incomplete resistance, combined with a certain degree of tolerance (Cubero, 1994). The study and characterization of host avoidance or resistance mechanisms would be of great importance in directing screening and breeding programmes for Orobanche control in pea (Rubiales et al., 2002). Resistance and avoidance against O. crenata have been identified in legumes. Avoidance because of reduced root biomass or root architecture has been identified in faba bean (Ter Borg, 1999) and lower Correspondence: A Pe´rez-de-Luque, Instituto de Agricultura Sostenible, CSIC, Apdo 4084, 14080 Co´ rdoba, Spain. Tel: + 34 957499242; Fax: + 34 957499252; E-mail: bb2pelua@uco.es Ó 2005 European Weed Research Society Weed Research 2005 45, 379–387