INDUCED RESISTANCE IN POTATO AGAINST GLOB ODERA-ROSTOCHIENSIS

Two ex-vernei tetraploid genotypes of potato and their parents were st udied for their resistance to G. rostochiensis Ro1/4. From tests made in vitro, on plants grown in Petri dishes, these genotypes decreased, but did not completely suppress the development of females as happens with all resistant genotypes containing the H1 gene. In pot tests, the level of resistance was nearly as strong as that conferred by the H1 gene. The possibility that differences exist in the activity of potato root diffusates was tested and refuted, some of the resistant genotyp es inducing greater hatching than the susceptible control. Two other r esistant genotypes produced slightly lower rates of hatching but the d ifference was insufficient to account for observed differences in resi stance. In the in vivo studies, it appeared that invasion of the roots by juveniles of G. rostochiensis induced an almost complete resistanc e to them and also to G. pallida. The possible role of phytoalexins or of PR proteins is discussed.