Sunflower (Helianthus annuus L.) response to broomrape (Orobanche cernua Loefl.) parasitism: induced synthesis and excretion of 7‐hydroxylated simple coumarins

Abstract

The interaction of the parasitic plant Orobanche cernua with resistant and susceptible cultivars of Helianthus annuus L. was investigated. Using different bioassays to evaluate the early stages of the parasite life cycle (germination, attachment, penetration, and establishment), differences were observed between O. cernua-resistant and O. cernua-susceptible sunflower varieties. Germination of O. cernua seeds in the presence of resistant sunflower roots was approximately half that of germination in the presence of susceptible roots, and germinated seeds displayed enhanced browning symptoms. Parasite radicles or host-tissue around the contact point turned brown after O. cernua attachment to sunflower roots, especially in the resistant varieties. These observations suggested the possible accumulation of toxic compounds as a defence strategy in the resistant sunflower varieties. Sunflower 7-hydroxylated simple coumarins may play a defensive role against O. cernua parasitism by preventing successful germination, penetration and/or connection to the host vascular system. This hypothesis is supported by the following data: (i) coumarins inhibited the in vitro germination of O. cernua seeds induced by the strigol analogue GR(24) and caused a browning reaction in germinated seeds and (ii) resistant sunflowers accumulated higher levels of coumarins in roots and excreted greater amounts than susceptible varieties in response to O. cernua infection.

Response of some chickpea (Cicer arietinum L.) genotypes to Orobanche foetida Poir. parasitism

“…The germination percentage decrease observed for the resistant genotypes/accessions could be related to the production of inhibitors rather than a decrease of root stimulants production, or a combination of both (Whitney and Carstein, 1981). Most reports available on this topic suggest that the eliciting activity of root exudates depends on the respective concentrations of germination stimulants and germination inhibitors in root exudates (Whitney, 1978;Serghini et al, 2001;El-Halmouch et al, 2006). Thus, germination inhibitors have been identified in the root exudates of fenugreek (Evidente et al, 2007).…”

“…Thus, germination inhibitors have been identified in the root exudates of fenugreek (Evidente et al, 2007). Also, phytoalexins have been reported as inhibitors of germination of broomrape (Serghini et al, 2001). The six chickpea genotypes induced radical browning of germinated seeds and then death of the parasite.…”

Characterization of resistance to crenate broomrape (Orobanche crenata) in a new small-seeded line of Tunisian faba beans

“…The origin of the low stimulatory capacities of 'XBJ90.03-16-1-1-1-1' root exudates was not elucidated in the present study. Most reports available on this topic (Cubero et al 1993;El-Halmouch et al 2006;Serghini et al 2001;Whitney 1978) suggest that the eliciting activity of root exudates depends on the respective concentrations of germination stimulants and germination inhibitors in root exudates. Recently, Mabrouk et al (2007a, b, c) showed that in pea, some nodulating strains of Rhizobium leguminosarum were inducing resistance to O. crenata.…”

History of the race structure of Orobanche cumana and the breeding of sunflower for resistance to this parasitic weed: A review

“…The non-existence of differential lines for new broomrape races makes defining broomrape races on the global level more difficult (Škorić et al, 2010). Genetic resistance to populations from Romania overcoming race F has been reported to be controlled by two independent dominant genes in line AO-548 (Pacure-connection with sunflower roots in the sunflower variety Cortés (Eurosemillas, Córdoba, Spain) resistant to Spanish O. cumana populations collected between 1994 and 1996 (Serghini et al, 2001).…”