Comparison of regeneration potentials in tissue cultures of primitive and cultivated tomato species (Lycopersicon sp.)

Regeneration capacities of two tomato cultivars: Potentat and Rutgers, and of three accessions of wild tomato species: <em>Lycopersicon peruvianum</em> PI 128650, <em>L. peruvianum var. dentatum</em> PI 128655 and <em>L. glandulosum</em> were studied using an universal medium suitable for regeneration of those plants from leaf pieces in tissue culture. Fragments of leaf blades were taken from plants raised in greenhouse conditions and placed on a modified MS medium containing 0.3 mg/l IAA and 3.0 mg/l BAP solidified with 1% agar. The explants were transferred every 4-5 weeks on fresh medium of the same composition. It was shown that all the three primitive tomato species revealed much higher multiplication coefficients than the two cultivars. Appropriate values were: 11 - for <em>L. glandulosum</em>, 8 - for <em>L. peruvianum</em>, 7 - for <em>L. peruvianum var. dentatum</em>, 4 - for <em>L. esculentum</em> cv. Potentat and 2 - cv. Rutgers. Completely regenerated plants were obtained from all the tested species, but organogenesis occurred almost two weeks earlier in wild tomatoes than in the culitivated varieties of <em>L. esculentum</em>.

Marker assisted identification of tospovirus resistant tomato genotypes in segregating progenies

The SCAR (Sequence Characterized Amplified Region) 'Sw-421' molecular marker is located at 1.0 cM from the Sw-5 allele, originated from Lycopersicon peruvianum (L.), which confers resistance to the tomato spotted wilt virus (TSWV). However, it had not been tested yet in advanced tomato populations. The goal of this study was to distinguish resistant homozygotes (Sw-5/Sw-5) and heterozygotes (Sw-5/Sw-5+) from susceptible (Sw-5+/Sw-5+) plants in crossing populations with the Stevens cultivar and advanced backcrossing populations by using 'Sw421' SCAR marker. The amplification of 940 bp and 900 bp bands characterized the resistant homozygotes and susceptible controls, respectively. A two band pattern (900 bp and 940 bp) was observed in heterozygote genotypes (Sw-5/Sw-5+), which confirmed the co-dominant inheritance mechanism of the marker. Fifty seven plants from the isogenic progenies were characterized based on bands pattern: 18 plants (31.6%) were identified as resistant homozygotes, 8 plants (14.0%) as resistant heterozygotes and 31 plants (54.4%) were characterized as susceptible. The SCAR 'Sw-421' marker is an important tool for selection and pyramid resistance alleles, mainly when other resistance sources to the TSWV are available, such as the Rey de los Tempranos source.

Screening Two Lycopersicon peruvianum Collections for Resistance to Tomato spotted wilt virus

The United States Department of Agriculture (USDA) Research Service and the Tomato Genetics Resource Center (TGRC) Lycopersicon peruvianum germplasm collections (16,335 plants from 285 accessions) were screened with the Tomato spotted wilt virus (TSWV) isolates TSWV6 from Hawaii, and Anwa-1 from Western Australia. Using TSWV6 to screen for resistance, 10,634 L. peruvianum plants from 280 accessions were screened for resistance, resulting in 168 (60%) accessions with 1,437 (14%) plants indicating resistance, with all 1,404 89S (Sw-5+/Sw-5+) and 1,456 89R (Sw-5/Sw-5) controls infected. When using Anwa-1 for screening, 864 (15%) of 5,701 L. peruvianum plants were uninfected from 106 of the 181 accessions tested, and 472 (95%) of the 495 89S and 421 (73%) of the 574 89R controls were infected. Of the 172 accessions tested with both isolates, 54 were resistant to one isolate but not the other. Additionally, more accessions from the USDA than from the TGRC collection indicated resistance. TSWV-resistant accessions were somewhat equally distributed throughout the L. peruvianum geographic range, with an observation that northern Chile and southern Peru seemed to have an unusually high portion of accession indicating resistance. The value of Sw-5 is discussed in relationship to potential additional sources of TSWV resistance.

Host-directed processing of Citrus exocortis viroid

Prolonged infection of tomato hybrid (Lycopersicon esculentum×Lycopersicon peruvianum) by Citrus exocortis viroid (CEVd) resulted in viroid-like enlarged structures, detected by gel electrophoresis. This population included two new enlarged variants or D-variants, D-87 and D-76, and three transient species or D-forms, D-38, D-40 and D-43. Sequence analyses exposed a locus near the terminal repeat region where major changes appeared consistently. In transmission tests to CEVd hosts, a variety of progeny populations were recovered, including progeny enlargements of and reversions to CEVd, as well as sequence fidelity to the inoculum. Transmission tests to citrus hosts of the genera Citrus, Poncirus or Fortunella were unsuccessful. The importance of host specificity to the recovery and processing of the various CEVd-related structures, as well as the temporal variability of progeny populations, was demonstrated.