The male-sterile gene ms-10 has been placed in cis with two flanking, selectable markers, Prx-2 (Peroxidase-2) and aa (anthocyanin absent). The gene order is: Prx-2 … (0.5 cM) … ms-10 … (5.0 cM) … aa. This construction allows the male-sterile gene to be transferred into breeding lines by selection of the codominant peroxidase marker. Once transferred, male-sterile genotypes can be selected at the seedling stage by the recessive aa marker, reducing the need to rogue fertile plants in the field. The transfer and propagation procedures made possible by these linkages should facilitate the use of genic male-sterility in the production of hybrid tomato seed.
Accessions of four tomato species, Lycopersicon esculentum Mill. (Le), L. pennellii (Corr.) O'Arey (Lpen), L. cheesmanii Riley (Lc), and L. peruvianum (L.) Mill., (Lper), and interspecific populations were irrigated with saline water under field conditions and concentrations of Na, K, Cl, Ca, and Mg in leaves and stems were determined. Potassium: sodium ratios in leaves and stems of salt-tolerant genotypes were higher under salinity and were moderately changed by salinity compared to the sensitive genotypes. In the tolerant wild accessions and F1(Le × Lpen), Cl concentrations in leaves and the ratio between Cl in leaves to Cl in stems were lower than in the sensitive Le cultivar. Regulation of the K: Na ratio was found in tolerant wild accessions and tolerant Le cultivars, while regulation of Cl concentration in leaves was found only in the wild germplasm. The effects of ion concentrations on dry matter of interspecific segregating populations, F2(Le × Lpen) and BC1(Le × (Le × Lpen)), were studied by regression analyses. Dry matter was positively correlated with the K: Na ratio in stems and negatively correlated with the Cl concentrations in leaves and stems, thus confirming the results obtained by comparison between the tolerant and sensitive accessions.
Salt tolerance of 59 cultigens of tomato (Lycopersicon esculentum Mill.), seven wild Lycopersicon accessions (acc.), and one interspecific hybrid was studied under arid field conditions. Evaluation of salt tolerance was based on relative total dry matter (RD) and relative total yield (RY), calculated as the ratio between performances of salinetreated and control plants. The tomato cultigens were irrigated with water having electrical conductivities (ECi) of 1.5 (control), 5, 10, or 15 dS·m−1. Considerable variation in salt tolerance was found among the cultigens, but at 15 dS·m−1 all showed reduced RD and RY (<0.6). The cultivar M82-1-8 (M82), one accession of L. cheesmanii (Lc), three accessions of L. pennellii (Lpen), three of L. peruvianum (Lper), and an interspecific F1 hybrid (M82 × Lpen acc. LA-716) were examined for RD at three salinity levels, ECi = 1.5, 10, and 20 dS·m−1, in three annual trials. The salt tolerance of Lpen and Lper were higher than those of M82 and Lc; the interspecific F1 was the most tolerant and was usually unaffected by even the highest salinity level. The results of this study indicate the existence of a genetic potential for high salt tolerance in wild Lycopersicon germplasm.
Quantitative trait loci influencing morphological traits were identified by restriction fragment length polymorphism (RFLP) analysis in a population of recombinant inbred lines (RIL) derived from a cross of the cultivated tomato (Lycopersicon esculentum) with a related wild species (L. cheesmanii). One-hundred-thirty-two polymorphic RFLP loci spaced throughout the tomato genome were scored for 97 RIL families. Morphological traits, including plant height, fresh weight, node number, first flower-bearing node, leaf length at nodes three and four, and number of branches, were measured in replicated trials during 1991, 1992, and 1993. Significant (P ≤ 0.01 level) quantitative trait locus (QTL) associations of marker loci were identified for each trait. Lower plant height, more branches, and shorter internode length were generally associated with RFLP alleles from the L. cheesmanii parent. QTL with large effects on a majority of the morphological traits measured were detected at chromosomes 2, 3, and 4. Large additive effects were measured at significant marker loci for many of the traits measured. Several marker loci exhibited significant associations with numerous morphological traits, suggesting their possible linkage to genes controlling growth and development processes in Lycopersicon.