Variability of interactions between barrel medic (Medicago truncatula) genotypes and Orobanche species

A number of broomrapes ( Orobanche spp.) are major threats for grain legumes in the Mediterranean area. Previous studies have shown very high levels of resistance to Orobanche crenata in Medicago truncatula with little variation among accessions hampering, therefore, its use for genetic analysis. In order to identify alternative systems for ulterior genetic and genomic analysis, we studied early stages of the interaction between M. truncatula accessions and a range of Orobanche species. We found significant differences in the induction of germination on Orobanche aegyptiaca , Orobanche foetida var. broteri , Orobanche minor , Orobanche nana and Orobanche ramosa seeds. Accessions also varied in the number of O. aegyptiaca , O. crenata , O. foetida var. broteri , O. nana and O. ramosa attachments supported. Applications of the synthetic germination stimulant GR24 increased the germination level of Orobanche cumana and O. minor . No attachments were observed for any of these species because of physical barriers typical of host resistance. On the contrary, increase of O. nana germination by GR24 led to an increase in number of attachments albeit the normal development of the nodules was stopped in a later stage. The genetic variation observed for induction of germination and subsequent attachment will be useful for isolating and characterising genes involved in early stages of Orobanche –host plant interaction and for the study of the biosynthetic pathways of production of germination stimulants.