Fava beans, broomrapes and radiation

Broomrapes (Orobanche spp.) belong to a genus of over 200 species of parasitic herbaceous plants. As they have no chlorophyll, they are totally dependent on other plants for their nutrients. As a result, they can produce serious damage to many legume crops and particularly becomes a limiting factor for the production of faba beans in the Mediterranean basin.

[Orobanche foetida (Chris B@rlow)]

Several traditional methods of pest control have been tried and tested, but none has been proven to be really effective against this parasitic plant. Research has mostly focused on breeding resistance into fava beans, but the resistance mechanisms governing the interaction between the parasite and the host are not yet well understood[1].

So, scientists thought, suppose we try to create new mutants through radiation mutagenesis[2]. Three faba bean genotypes were used in this study, the variety 'Badï' (characterized by high productivity in Orobanche-free soils and susceptibility to Orobanche foetida) and two mutant lines P2M3 and P7M3 (derived via radiation mutagenesis) were selected for field evaluations because of their higher resistance to Orobanche foetida.

The field experiments showed that low induction of seed germination is a major component of resistance in these lines against broomrapes. This was confirmed by in vitro experiments with root exudates. Also, reduction in infection was accompanied by the continuously enhancement of the peroxidase activity, the polyphenol oxidase activity and the phenylalanine ammonia lyase activity in faba bean roots.

The data suggests that these enzymes play a role in faba bean resistance to Orobanche foetida. Management of Orobanche by way of crop selection based on these enzyme systems is a possible option.

[1] Rubiales et al: Characterization of Resistance Mechanisms in Faba Bean (Vicia faba) against Broomrape Species (Orobanche and Phelipanche spp.) in Frontiers in Plant Science - 2016
[2] Mejri et al: Orobanche foetida resistance in two new faba bean genotypes produced by radiation mutagenesis in International Journal of Radiation Biology – 2018