Identification of PCR-based Molecular Markers Linked to B, A Carotenoid-related Gene in Tomato

β-carotene is the principal provitamin A caroteniod found in tomato fruits and makes a significant contribution to the fruits nutritional value. The dominant B gene conditions high levels of β-carotene in ripe tomato fruits. PCR-based molecular markers, including random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP), were used to identify marker linkage to the B locus. The study was conducted using a near-isogenic line (NIL) of the cultivar Rutgers isogenic for the B locus and bulk segregant analysis of an interspecific F2 population segregating for the B locus, which was derived from the cross of Lycopersicon cheesmanii accession LA 317 × L. esculentum cv. Floradade. Sixty-four AFLP primer pairs and 1018 arbitrary RAPD primers were screened for polymorphism between the pair of NILs and between the two bulks. A number of amplified RAPD and AFLP products were identified that were present in one line or bulk but not the other. Marker linkage with the B locus was confirmed by checking individual samples from the F2 and BC populations. Two RAPD markers were confirmed tightly linked with the B phenotype using the interspecific F2 population. Similarly, a single AFLP marker was identified with close linkage to the B phenotype using the NIL F2 population. The markers identified in this study can be useful in breeding programs with marker assisted selection and, if very tightly linked, as a starting point to isolate the gene.

A Search for Resistance in Lycopersicon spp. to Nacobbus aberrans

Accessions of Lycopersicon cheesmanii, L. chmielewskii, L. esculentum var. cerasiforme, L.hirsutum, L. parviflorum, L. peruvianum, L. pennellii, L. pimpinellifolium, and three interspecific hybrids of L. peruvianum with L. esculentum, were screened for resistance to the false root-knot nematode (Nacobbus aberrans) in greenhouse tests. Variability in nematode reproduction levels was observed within L. chmielewskii accessions LA 2695 and LA 2663 in initial tests with N. aberrans from Argentina; however, interspecific hybrids of L. esculentum cv. UC-82 × L. chmielewskii LA 2695, L. esculentum cv. UC-82 × L. chmielewskii LA 2663, and all the parent plants were susceptible in subsequent tests to the isolate of N. aberrans from Argentina and to an isolate from Mexico. The interspecific hybrids that possess the gene Mi and additional novel resistance to Meloidogyne spp. (root-knot nematodes) and all other exotic tomato accessions tested were susceptible to N. aberrans in our tests. Thus, we have been unable to identify or confirm resistance to two N. aberrans isolates in a range of Lycopersicon germ plasm accessions, including those that possess genes for resistance to root-knot nematodes.

465 PB 324 QTL MAPPING AND MARKER-ASSISTED SELECTIONUSING INDEPENDENTLY GENERATED INBRED BACKCROSS TOMATO POPULATIONS

The inbred backcross (IBC) breeding method is being used to introgress genes controlling high fruit soluble solids from a wild tomato species (Lycopersicon cheesmanii f. minor) into a California processing tomato cultivar (Lycopersicon esculentum cv. UC204B). One IBC tomato population (i.e. P1: 106 lines) is being used to map quantitative trail loci (QTL) for soluble solids and other traits. A genetically related but independently generated IBC population (i.e. P2: 96 lines) is being used to lest the efficiency of QTL-linked RPLPs for indirect marker-assisted selection (MAS) to improve soluble solids. P1 was analyzed for fruit quality traits in a replicated field design over 2 years. Twelve P1 lines were significantly greater than UC204B for soluble solids and also had acceptable fruit weights and horticultural traits. All twelve lines have been publicly released for further breeding efforts. In P1. we have identified RPLP markers that have significant correlations to QTL. Some of these markers map to regions previously reported by other researchers to contain QTL for the same traits. We will use 70-80 markers spaced approximately 10-20 cM apart across the genome to screen PI and map QTL. The RPLP analyses are currently in progress. P2 was replicated for one year using the same field design as P1. and analyzed for the same traits. P2 will be screened with QTL-linked RFLPs identified in P1 to test the consistency of QTL locations between independently derived populations. P2 lines selected using RFLP data will be compared to P2 lines identified by classical selection indices. This will indicate if MAS for QTL is effective in a population (P2) genetically independent from the mapping population (P1).

SALT TOLERANCE OF A SELECTED LINE FROM THE CROSS BETWEEN A WILD, TOLERANT TOMATO SPECIES (LYCOPERSICON CHEESMANII, ECOTYPE LA 1401) AND A CULTIVATED SPECIES (L. ESCULENTUM MILL.)

A salt-tolerance selected F5 generation from a cross between the wild tomato species, Lycopersicon cheesmanii, ecotype LA 1401, and the cultivated species, L. esculentum Mill. (cv Heinz 1350) was compared to the wild parental line in a solution culture experiment to determine the effects of selection on salt tolerance, and ion discrimination and accumulation characteristics in the selected line. Seedlings were transplanted to nutrient solutions at the 3 to 4-leaf stage of growth and after a 1-week period of adjustment, were salinized at 25 mM NaCl day-1 (approximately -1 bar osmotic potential) to final salt concentrations of 0, 50, and 100 mM. Plasmalemma and tonoplast vesicles were isolated from fresh root samples, and ATPase and Na+/H+ antiport activity was determined using fluorescence assays. The selected line restricted Na uptake into the shoot and maintained higher shoot K+ than did the wild parent. Growth rate under salinity was greater in the selected line than in the wild species, but relative salt tolerance was higher in the wild parent. Interspecific hybridization appears to be a useful process for the transfer of salt tolerance characters from wild to cultivated tomato.

Use of Molecular Markers to Locate Quantitative Trait Loci Linked to High Soluble Solids Content in a Hybrid of Lycopersicon cheesmanii

An interspecific hybrid was made between an accession of Lycopersicon cheesmanii f. minor Riley (LA 1508) from the Galapagos Islands, Ecuador, and L. pennellii (Corr.) D'Arcy (LA 716). LA 1508 was used because of its high soluble solids content (SSC). It was crossed with LA 716 to test for linkage between isozymes and morphological markers and loci conditioning high SSC. For both accessions, chromosome numbers are equal and there are large differences between SSC and no barriers to crossing. Modified BC1 populations derived from the hybridization were assayed for isozyme markers using starch gel electrophoresis. Associations between marker loci and quantitative-trait loci (QTL) conditioning high SSC were determined using analysis of variance. Six isozymes located on five chromosomes and one morphological marker had significant associations with SSC, indicating linkage to QTL. Digenic epistatic interactions between pairs of independent markers did not appear to play an important role in the interactions between QTL that condition SSC.

Starch and Sugar Accumulation in Two Accessions of Lycopersicon cheesmanii

A study using Lycopersicon cheesmanii Riley LA 1449 (typicum), a low soluble solids content (SSC) accession, and L. cheesmanii f. minor LA 528 (minor), a high SSC accession, was undertaken to characterize the accumulation of starch, sugar, and total SSC. Fruit of each accession was sampled throughout development to identify differences in SSC, starch accumulation, and sugar distribution. Osmetric analysis indicated that the minor race had higher SSC content throughout the ontogeny of fruit development than the typicum. Typicum contained more starch than minor, and both accessions showed a rapid decline in percent starch as the fruit ripened. Sucrose remained low throughout all stages of fruit development for both accessions. Glucose increased in the minor and declined in the typicum. Fructose increased in both accessions. Total reducing sugar content at the full ripe stage was higher in minor than the typicum.

Composition chimique de sèves xylémiques du genre Lycopersicon (Solanaceae) en relation avec l'environnement. II. Effet de la salinité

Two tomato species, Lycopersicon esculentum Mill. var. Edkawy and Lycopersicon cheesmanii (Hook) C. H. Mull, ecotype LA 1138, were grown in saline (100 mM NaCl) conditions. The study of weight increase of these two species showed that L. cheesmanii was the least affected by salinity. The chemical composition of xylem sap (cations, anions, amino acids) was analysed by high performance liquid chromatography. This study demonstrated a control of NaCl transport in L. esculentum, but not in L. cheesmanii. Moreover, ammonium appeared in xylem sap of L. cheesmanii in saline culture. Different hypotheses about its origin are discussed. Key words: ammonium, salinity, xylem sap, Lycopersicon.