Search Results
Abstract
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.
Abstract
Seed extracts of a number of fresh market cultivars of tomato (Lycopersicon esculen-tum Mill.) were subjected to starch gel electrophoresis and stained for alcohol dehydrogenase activity to investigate the possibility of utilizing allozymic variation to determine genetic purity of F1 hybrids. Of the varieties tested 46% proved amenable to the test. This method offers a practical and rapid means of estimating seed contamination frequencies in commercial seed lots as well as distinguishing hybrids from parental lines in the field.
Two chromosomal segments from the wild tomato L. chmielewskii have been introgressed into the L. esculentum genome. Using molecular markers they have been mapped to the middle and terminal regions of chromosome 7 (7M and 7T, respectively). This study was conducted to further clarify the physiological influence of the introgressed segments on tomato soluble solids, and other fruit and yield parameters. Sixty-four BC2F5 recombinant inbreds were developed from a cross using LA1501 (L. esculentum line that contains both fragments from L. chmielewskii) as the donor parent, and VF145B (processing cultivar) as the recurrent parent. Recombinant inbreds were classified in four groups (++: inbreds without either of the fragments, 7M+: with only the 7M fragment, +7T: with only the 7T fragment and, 7M7T: with both fragments) based on RFLP information, and then compared to each other for all the parameters under study. Inbreds homozygous for the 7M fragment displayed greater soluble solids (26%) and higher pH (0.10) than the control group (++), through a physiological mechanism related to water uptake. The 7L fragment did not influence either soluble solids or pH, but was observed to significantly increase fruit yield by 11%. A gene or genes that increase yield without affecting soluble solids or pH may have potential in the development of commercial cultivars.
Tomato (Lvcopersicon esculentum) line E427 contains Fusarium wilt resistant gene I-3 on chromosome 7 and I-2 (and presumably the linked I) genes on chromosome 11. E427 was crossed with `Bonny Best' (i, i-2, i-3) and backcrosses (BC) to `Bonny Best' and F2, seed were obtained. Self pollination of 187 BC and 150 F2 plants were made. Progeny were screened against Fusarium races 1, 2, and 3 and lines with recombinant ratios were self-pollinated and rescreened until homozygous. Five lines were resistant to races 2 and 3 but susceptible to race 1. These had the isozyme band got-2 linked to I-3, RFLP markers linked to I-3 and no RFLP markers linked to I-2. Five lines were resistant to race 1 but susceptible to races 2 and 3. These had the susceptible qot-2 band and no RFLP markers linked to I-3 or I-2. F2 complementation tests of 2 of these lines with `Manapal' (I) indicated they contained I. Three lines were resistant to race 2 but susceptible to races 1 and 3. These had the susceptible qot-2 band, I-2 linked RFLP markers, and no I-3 linked RFLP markers.
Tuberization and stolonization of cuttings were used as a model system to assess response to photoperiod in segregating potato progenies. The progenies were from backcrosses of a diploid hybrid between Solanum tuberosum and the short day requiring S. berthaultii to both parent species. Restriction Fragment Length Polymorphism (RFLP) analyses had been performed on these progenies as a part of other investigations. The RFLP maps were used to identify the loci controlling the photoperiod responses characterized by the cuttings. In the S. berthaultii backcross population, one locus appeared to control the response of cuttings only under long photoperiods, and coincided with a locus detected for stolonization on whole plants; a second locus was effective for tuberization under short photoperiods but was not detected with certainty under long photoperiods. Data analysis for the second backcross population is currently underway.
Tomato yellow leaf curl virus (TYLCV), a heterogeneous complex of whitefly-vectored geminiviruses, is a serious production constraint of tomato (Lycopersicon esculentum Mill.) in Asia, the Middle East, and the Americas. In this study we report on mapping of a DNA fragment introgressed into cultivated tomato presumably from the wild species L. hirsutum Humb. and Bonpl. and found to be associated with TYLCV resistance. To locate introgressions of wild tomato alleles in TYLCV-resistant tomato line H24, its DNA was digested with six restriction enzymes and probed with 90 RFLP markers evenly spaced throughout the genome. This polymorphism survey revealed the presence of one wild tomato introgression each on chromosomes 8 and 11. Plants of a F2 cross between H24 and a susceptible tomato line were probed with randomly amplified polymorphic DNA (RFLP) markers linked to the targeted regions and F3 families were developed by self-pollination of F2 plants that carried none, one, or both introgressions in either homozygous or heterozygous states. Plants of F3 families, parents, and control tomato line Ty52 (homozygous for the Ty-1 allele for TYLCV tolerance) were exposed to viruliferous whiteflies (Bemisia tabaci Gennadius) in greenhouses at the Asian Vegetable Research and Development Center, Taiwan, and the University of Agricultural Sciences, Bangalore, India. Results indicated that F3 families homozygous for the introgression on chromosome 11 were resistant to TYLCV at both locations. Additional probing showed that the chromosome 11 introgression spanned markers TG36 to TG393, covering a distance of at least 14.6 centimorgans. This is the first report of TYLCV resistance in tomato mapped to chromosome 11.