ISHS Acta Horticulturae 71: Symposium on Carnations
INHERITANCE OF PATHOGENICITY IN PHYTOPHTHORA PARASITICA |
| Authors: | N. Maia, P. Venard |
| Abstract:
Our preliminary results concern genetics of pathogenicity in the species Phytophthora parasitica, parasite on Carnation cuttings. On freshly sectionned cuttings most strains of P h y t o p h t h o r a penetrate at the bottom of the cutting, while on cuttings placed for seven days in rooting conditions before inoculation, only some strains are able to induce symptoms, (Ricci, Bonnet, 1977). Crosses were set up between two strains; isolate 26 an A2-compatible type isolated from Carnation, and isolate 44 an A1-compatible type isolated from Citrus. On non rooted cuttings (OD) the two parental strains differ only by the extent of necrosis noted on the stem; on rooted cutting (7D) only the strain 26 is still pathogenic. The inheritance of pathogenicity was examined in forty-five progenies. These, together with the parents, were inoculated on 0Day - and 7 Days - cuttings. On the former, the necrosis length comparison of the F1-hybrid strains, showed a near normal distribution with a mean lying between the two parents: some strains were less aggressive than the parent 44 or more aggressive than the parent 26. On 7D-cuttings, we have noted the rate of infection: the repartition was bimodal with two populations grouped around the values of the two parents. We can propose the following hypothesis: on 0D-cuttings, the difference between strains are quantitative and the most likely explanation is that pathogenicity at this level of interaction is under polygenic control. On 7D-cuttings, the difference between strains would be qualitative and under a mono or oligogenic control. The results have to be confirmed by F2 studies. | |
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