De novo morphogenesis on tomato thin cell layers and variation for genetic recombination among plantlets regenerated from tissue culture

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Virginia Tech


De novo shoots, roots, and flower buds were regenerated on thin cell layer explants excised from pedicel tissue of tomato. Direct shoot organogenesis was greatest when media contained 10µM kinetin and 0.001µM indole-3-acetic acid (IAA); however, shoot regeneration was increased in subsequent experiments by substituting 10 µM zeatin or 10 µM benzyladenine for kinetin. Root formation occurred when media contained higher (0.1 and 10µM) auxin concentrations. Flowers were formed on elongated shoots with several leaves when media contained 10µM IAA and 0.1µM kinetin.

Competence for de novo shoot morphogenesis was tested on thin cell layers of eleven tomato cultivars. All tomato cultivars formed shoots directly on thin cell layer explants at varying frequencies (29%-63%). The mean number of shoots per explant was greatest for 'Large Red Cherry', 'Ohio 7814' and 'BL 6807', and poorest for 'Campbell 1327' and 'Red Alert'. Active cell divisions were observed in subepidermal cells during the first week of culture, and meristematic centers of dividing cells were evident after 2 weeks. Well developed shoot apices were observed on 50% of the explants 4 weeks after culture initiation.

Shoot morphogenesis was compared among tomato plants placed into micropropagation, callus, and thin cell layer tissue culture systems. More shoots were produced on thin cell layer explants than on cotyledon calli, or micropropagated shoot tips. Genetic recombination rates and map distances were compared among hybrid plants grown in the greenhouse and regenerated from the aforementioned tissue culture systems. Increased recombination rates and map distances were detected between the sunny (sy) and baby leaf syndrome (bls) genes on chromosome 3, and between the white virescence (wv) and anthocyanin reduced (are) genes on chromosome 2. The percent change in the former ranged from 4.5%-5.9% for micropropagated shoot tips, 3.7%-8.5% for plants from cotyledon calli and 2.8%-5.9% for plants from thin cell layers. The percent change between the wv and are loci ranged from 4.5%-6.1% for micropropagated shoot tips, and 3.2%-5.0% and 3.9%-5.7% for plants from cotyledon calli and thin cell layers, respectively. Conversely, a decreased map distance was observed between bls and the solanifolia (sf) locus which is more distal to the centromere on the same arm of chromosome 3 as bls. Changes in recombination rates among plants regenerated from tissue culture may result from an influence of the tissue culture process on meiosis of regenerated plants.