A high level of resistance toGlobodera pallida pathotypes Pa2 and Pa3 exists inSolanum spegazzinii, a wild relative of potato (S. tuberosum ssp.tuberosum). Here we report the mapping of loci involved in quantitatively-inherited nematode resistance with the use of RFLPs. One major locus,Gpa, was mapped on chromosome 5 and two minor loci on chromosomes 4 and 7 ofS. spegazzinii. Additionally, the contribution of the susceptible parent to nematode resistance was determined. TheGpa locus was solely responsible for the high resistance level found in the segregating population. However, the RFLP marker closely linked to this resistance locus showed a distorted segregation, with a shortage of plants having the resistance linked allele. Our results indicate that a prediction of the genetic constitution of a quantitative trait based solely on phenotypic observations can lead to erroneous conclusions.

The compositions of glycosidic-bound steroidal alkaloids (SA) of Solanum species used in potato breeding were assessed by capillary gas chromatography using simultaneous nitrogen-specific (NPD) and flameionisation detection (FID) . High concentrations of solanidine glycosides and other steroidal glycoalkaloids, amongst which the teratogenic SA solasodine, were found in tubers and leaves of wild species . In addition unidentified compounds were found, which were most probably SA as was shown by their NPD/FID response ratios . The total glycoalkaloid contents varied from 123 to 7348 mg/kg fresh weight . Tubers of cultivars, corresponding in small size and grown under the same conditions as tubers of the wild species, showed contents of solanidine glycosides which were 2-3 times higher than those of field-grown normal tubers (126-721 vs 40-360 mg/kg fresh weight, respectively) . In some cases the SA compositions of the tubers were markedly different from those of the leaves of the same plant or they varied between accessions of the same species . Also the growing conditions appeared to influence the composition quantitatively and qualitatively .The consequences for potato breeding of utilizing wild Solanum species containing potentially hazardous levels of SA are discussed .

We report the identification and mapping of two quantitative trait loci (QTLs) of Solanum spegazzinii BGRC, accession 8218-15, involved in resistance to the potato cyst-nematode Globodera rostochiensis pathotype Ro1, by means of restriction fragment length polymorphisms (RFLPs). For this purpose we crossed a susceptible diploid S. tuberosum with the resistant S. spegazzinii, and tested the F1 population for resistance to the Ro1 pathotype. Since the F1 segregated for the resistance, the S. spegazzinii parent was concluded to be heterozygous at the nematode resistance loci. For the mapping of the resistance loci we made use of RFLP markers segregating for S. spegazzinii alleles in the F1. One hundred and seven RFLP markers were tested in combination with four different restriction enzymes; 29 of these displayed a heterozygous RFLP pattern within S. spegazzinii and were used for mapping. Analysis of variance (ANOVA) was applied to test the association of the RFLP patterns of these markers with nematode resistance. Two QTLs involved in disease resistance to Globodera rostochiensis pathotype Ro1 were identified and mapped to chromosomes 10 and 11 respectively.

A backcross population, derived from the cross (S. tuberosumxS. spegazzinii)xS. tuberosum was used to map QTLs involved in nematode resistance, tuber yield and root development. Complete linkage maps were available for the interspecific hybrid parent as well as the S. tuberosum parent, and interval mapping for all traits was performed for both. Additionally, the intra- and inter-locus interactions of the QTLs were examined. The Gro1.2 locus, involved in resistance to G. rostochiensis pathotype Ro1, that was previously mapped in the S. tuberosumxS. spegazzinii F1 population, was located more precisely on chromosome 10. A new resistance locus, Gro1.4, also conferring resistance to G. rostochiensis pathotype Ro1, was found on chromosome 3. Different alleles of this locus originating from both parents contributed to the resistant phenotype, indicating multiallelism at this locus. No interlocus interactions were observed between these two resistance loci. For resistance to G. pallida no QTLs were detected. One minor QTL involved in tuber yield was located on chromosome 4. Two QTLs involved in root development and having large effects were mapped on chromosomes 2 and 6 and an epistatic interaction was found between these two loci.

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