VARIABILITY AMONG RACE 1 STRAINS OF R. SOLANACEARUM PATHOGENIC ON POTATO IN GUADELOUPE AND BREEDING FOR RESISTANCE.
Prior P1., Mathurin P2., Ellisèche D3., Béramis M1., Kiehl C1., Bart S1., Darrasse A1., Dardaine A1.
1
2 INRA-URPV, Laboratoire d’Amélioration des Plantes, BP 515, 97165, Pointe à Pitre Cedex, Guadeloupe (FWI).
3 INRA, Station d’Amélioration de la Pomme de Terre et des Plantes à Bulbes, Domaine de Kéraiber, 29260 Ploudaniel, France
Thirty strains of R. solanacearum isolated from potato plants at different locations in Guadeloupe were compared with respect to biochemical and pathogenicity on tobacco and aggressiveness on potato cultivars Korrigane, Desiree and LT7, which are susceptible, moderately resistant and resistant, respectively. Strains were grouped into four profiles differing in biovar (1 or 3), agressiveness, hypersensitivity on tobacco and resistance to the antibiotic spiramycin. This strain variability was factored into a study on resistance in potato genotypes, including three commercial cultivars and five populations of true potato seeds (TPS) hybrids. In addition, different polyclonal antisera were produced with high titers and specificity for ELISA diagnosis of latent stem and tuber infection by R. solanacearum .
Resistance was evaluated simultaneously in the greenhouse and in the field and under natural and artificial infections using a mixture of four selected strains representative of each profile. Disease severity significantly increased in plants inoculated in the field relative to those tested in the greenhouse. Nevertheless, the relative degree of susceptibility in potato material was consistent regardless of environmental conditions and tuber or TPS planting materials. This makes reliable first step for screening potentially resistant potato materials in the greenhouse.
Eighteen bacterial wilt resistant lineages were selected in Guadeloupe within parental bacterial wilt resistance sources BW1, BW2, BW3 and BW4 provided by CIP. These lineages were crossed with different commercial potato cultivars and few hybrids, previously issued from a multilocal fields evaluation program assessing agronomic and technical values in the French West Indies environnement. In 1992 and 1993, 223 families were selected from the total progenies obtained, following field screenings under natural inoculum constraints. These were multiplied and evaluated for BW resistance in the field, following mixed inoculation with four strains representative of each profile. All plants latently infected in the stem and/or tubers were discarded and 55 healthy families were retained and multiplied. After this different selection 21 potato clones with a very high resistance level were tested and indexed for bacterial populations (30 tubers per clone). Currently, 10 promising clones are being propagated and will be further evaluated on a larger scale.
