Test de descendance pour la résistance àGlobodera pallida Pa2/3 Stone chez la pomme de terre

Résumé

Un test de descendance pour la résistance àGlobodera pallida Pa2/3 est décrit. Il consiste à déposer 3 juvéniles sur racine pivotante issue de graine de pomme de terre, cultivée en boîte de Petri. On dénombre les femelles formées et on analyse les fréquences observées sur une centaine de graines par famille. L'influence de quelques facteurs sur la puissance du test est étudiée: longueur des racines lors du dépôt des juvéniles, conditions de culture des plantules, niveau de ploïdie du matériel étudié, état physiologique des juvéniles utilisés comme inoculum. Tous ces facteurs influent particulièrement sur le déterminisme du sexe, donc sur le nombre de femelles développées, et par conséquent sur la puissance du test. Accessoirement, la nature épigénique du déterminisme du sexe deG. pallida est confirmée.

Summary

A test to assess potato progeny resistance toGlobodera pallida Pa 2/3 has been developed. About 100 seeds per cross were grown on an agar medium in Petri dishes. Each tap root was inoculated with three juveniles taken from a population (Chavornay) which had been selected previously for being suitable for this kind of test. The number of females formed per seedling was determined and the observed frequencies analysed to define resistance.

Certain factors known to have an effect on the efficiency of the test have been examined: root length at inoculation time, growth conditions of seedlings, ploidy level of tested material, physiological condition of juveniles used as inoculum. All these factors can affect the proportion of females which develop and therefore the efficiency of the test. Inoculation has to be done as soon as possible (Table 1) and the seedlings held under favourable growth conditions (Tables 2 and 3). Juvenile development was best in tetraploid material (Table 4). In contrast, ageing the inoculum in the cold had no effect on the progeny test (Table 5).

The test, when used under the right conditions, would enable the breeder to choose among different crosses those in which resistance is best expressed in the progeny. It would allow quantitative inheritance studies of resistance toG. pallida. In addition, this study has further confirmed the effect of external factors on sex determination inG. pallida.