Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress
Salsomaggiore Terme, Italy - 26/29 September, 2001
SPECIALISATION OF COLLETOTRICHUM LINDEMUTHIANUM ON TWO HOST SPECIES, PHASEOLUS VULGARIS AND P. COCCINEUS
SICARD D.*, PENNINGS P.**, GRANDCLÉMENT C.***, ACOSTA J.****, SHYKOFF J.**
* Dipartimento di Biotecnologie Agrarie ed Ambientali, Università degli Studi di Ancona, Via Brecce Bianche, 60131 Ancona, Italy
** Laboratoire d’Ecologie, Systématique et Evolution, bat 362, Université Paris-Sud, 91405 Orsay cedex, France
*** Laboratoire de Phytopathologie Moléculaire, bat 630, Université Paris-Sud, 91405 Orsay cedex, France
**** Instituto Nacional de Investigaciones Forestales y Agropecuarias, Campo Experimental Valle de México, Apdo. Postal 10, 56230 Chapingo, México
Parasite varied in their host specificity from highly host specific to host generalist. Some parasite may have a limited host range because they have limited contact with other host species. This can be the case when either the host species or the parasite have low dispersal. Alternatively, host specificity could arise because of adaptive specialisation. If adaptive constraints are responsible then parasite fitness will reduced on novel host species.
We investigated whether fungal strains of Colletotrichum lindemuthianum isolated from two bean species, Phaseolus vulgaris and P. coccineus, have equal ability to attack the two hosts. This fungus is the causal agent of bean anthracnosis and is able to attack P. vulgaris, a selfer, and P. coccineus, an outcrosser, both in cultivated conditions and in wild populations. Wild P. vulgaris and P. coccineus are found in sympatry in Mexico and some of these populations harbour the fungus. Cross-inoculations experiments between fungus strains and plants of the two host species coming from 6 wild populations in the state of Morelos, Mexico were carried out.
The populations of P. coccineus were more resistant to strains isolated from P. vulgaris than to strains isolated from P. coccineus and vice-versa. This result was also found when P. coccineus and P. vulgaris were sympatric. Therefore, a specialisation of the fungus on its host species of origin was found. Within the two host species, we tested for local adaptation of fungi on their host populations of origin. We found evidence for local adaptation of the fungus on P. vulgaris but not on P. coccineus. This could be because of differences in gene flow between populations related to the contrasting breeding systems of the two bean species. Molecular variation between fungi strains isolated from the two bean species and gene flow between the two bean species are currently studied.