Selection of tomato plants supposedly tolerant to tomato yellow leaf curl virus (TYLCV), based solely on the absence of symptoms in an infested field can be misleading. An inoculation routine was therefore established to avoid escapes and to overcome difficulties associated with the age of the plant at the time of infection. The inoculation routine was applied to a selection of resistant/tolerant individuals generated through a diallel F, cross and to F2 segregating populations originating from three wild tomato species described as tolerant to TYLCV: Lycopersicon peruvianum EC 104395, Lycopersicon pimpinellifolium Hirsute and Lycopersicon chilense LA 1969. Clear differences were observed between susceptible symptomatic and tolerant symptomless tomato genotypes, indicating that the uncertainty resulting from escapes, from different levels of inoculum, and from the time of inoculation, can be eUminated. The genes involved in tolerance provided different levels of protection; combinations of various tolerant sources and levels in a single genotype gave a higher level of tolerance. Differences in level of protection were found between genes from the same source and between sources; none ofthe sources tested had complete dominance. The results obtained with the F2 segregating population showed that tolerance from L. pimpinellifolium is controlled by one major gene, that from L. chilense by two genes, and that from L. peruvianum by three genes with no dominant effect. The combination of sources for resistance can thus have positive or negative synergistic effects, or no effect. We suggest that a maximal level of tolerance can be obtained by the additive effect of the partly dominant genes from L. pimpinellifolium and L. chilense.

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The alkaloid profiles and morphological traits of the capsules of Papaver bracteatum, P. pseudo-orientale, and their hybrids were studied. Dominance of the hexaploid parent P. pseudo-orientale was observed for various characters. A genetic model assuming allelic additive effects and polysomic inheritance was elaborated for the control of isothebaine content in the capsules. The distribution of thebaine content in the segregating generations, F2 and BCF1 was evidence of the transfer of genes from the diploid parent P. bracteatum in the gametes of the interspecific hybrid and their expression in its progenies. These findings indicate the potential use of inter-specific hybrids between the Oxytona species in the breeding of cultivars for industrial or ornamental purposes.

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A RAPD marker, linked to the Tm-2 a gene engendering TMV resistance in tomatoes, was identified. The validity of the RAPD marker was corroborated by screening several tomato varieties, and correctly identifying those which carried Tm-2 a, as well as by F2 segregation analysis. All tested resistant varieties descending from a common Lycopersicon peruvianurrdesculentum ancestor, LA1791, exhibited this marker.