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The wild nightshade Solanum lycopersicoides (accessionLA2951) was backcrossed to the cultivated tomato (Lycopersicon esculentum cv ’VF36’), then inbred through single-seed descent for several generations. Over 300 backcross-inbred families thereby derived were genotyped at 139 marker loci, consisting of RFLPs, allozymes, and monogenic morphological markers, to identify introgressed S. lycopersicoides chromosomes and segments thereof. The pattern of genotypes observed in the lines indicated a high degree of overall synteny between the S. lycopersicoides genome and that of tomato. Two putative single-copy RFLP probes revealed secondary loci in this wide cross. Recovery of the L. esculentum genome was more rapid than expected, with an average value in the BC2 generation of 97.8%, versus the expected value of 87.5%. This was due to widespread segregation distortion that favored L. esculentum alleles as well as a tendency for plants homozygous for in- trogressed segments to be partially or completely male-sterile, thereby preventing the fixation of S. lycopersicoides markers in many lines. Despite these difficulties, nearly every S. lycopersicoides marker (or approximately 98% of the genome, measured in centi Morgans) was represented in at least 1 backcross-inbred line, with only a region on chromosome 4L missing from the population as a whole. Although the extent of transmission and fixation of introgressed segments varied according to chromosome, overall approximately 66% of the S. lycopersicoides genome was represented by homozygous in- trogressions with sufficient fertility to reproduce by self-pollination. An excess of terminal (vs. interstitial) segments was noted, and putative heterozygous substitutions for chromosomes 6, 7, 8, and 10 were found. Recombination within certain introgressed regions was reduced over 100-fold. These backcross-inbred lines are expected to facilitate the genetic analysis of traits identified in S. lycopersicoides and their transfer into horticultural tomatoes. [ABSTRACT FROM AUTHOR]

Twenty-one polymorphic and 17 monomorphic cucumber ( Cucumis sativus L.) isozyme loci were identified in 15 enzyme systems. Seven of the polymorphic loci ( Ak-2, Ak-3, Fdp-1, Fdp-2, Mpi-1, Pep-gl, and Skdh) had not been described previously. Segregation in F and BC families for isozyme and morphological loci demonstrated agreement with the expected 1∶2∶1 and 1∶1 segregation ratio ( P<0.01). Nine morphological markers were found to be linked to isozyme loci and were integrated to form a map containing four linkage groups spanning 584 cM with a mean linkage distance of approximately 19 cM. Linkage groups (A to D) contain the following loci in genetic order: A psl, Pep-la, B, Per, dm, Pgm, Mpi-1, Idh, Ar, Fdp-1, Ak-2, Pgd-1, Mpi-2 and gl; B lh, Mdh-2, Pep-gl, Pgd-2, Fdp-2, Ccu, Mdh-3, Ak-3, ll, de, F and Mdh-1, and Gr; C cor, Gpi, and Skdh; D Tu and ss. This study detected four new linkages between morphological markers ( dm-psl, de-ll, ll-F, and de-F) and confirmed previously reported linkages, dm-Ar and Tu-ss. The isozyme/morphological map constructed in this study led to a more comprehensive understanding of the genetic relationships between several economically important traits. [ABSTRACT FROM AUTHOR]

A 58-point genetic map was constructed with RFLP, RAPD, isozyme, morphological, and disease-resistance markers spanning 766 cM on ten linkage groups for a cross within the cultivated cucumber ( Cucumis sativus var. sativus). Relatively few DNA polymorphisms were detected, agreeing with previous studies documenting a narrow genetic base for cucumber. Most RFLPs within the cultivated cucumber appear to be changes at restriction-enzyme sites. Sixty-four percent of RAPD markers that fit expected ratios at P<0.001 were unlinked, possibly due to poor amplification and the inefficiency of dominant markers to detect linkage in an F family. A 70-point linkage map, spanning 480 cM on ten linkage groups, was constructed with RFLP, isozyme, morphological, and diseaseresistance markers for a cross between the cultivated cucumber and the wild or feral C. sativus var. hardwickii. Unlinked markers and more linkage groups than chromosome pairs indicated that both maps were not saturated. Twentyone markers doubly segregated in both families and regions of colinearity were identified. [ABSTRACT FROM AUTHOR]