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- Author or Editor: Dae-Geun Oh x
The tangerine-virescent (tv) mutation was reported as a single gene somaclonal variant from tissue culture (Evans and Sharp 1963). A replicated field trial was conducted to characterize variation and stability in the phenotype of this tv somaclone and to compare it with the inbred parent from which it was reportedly derived.
Heritability and stability of the tv somaclonal variant was measured by comparing R3 end R4 lines of sexual progenies of the original tv variant and with its sexually derived inbred parent UC82B. Several additional variants were observed in these tv lines, including fruit shape, days to first flower, fruit weight, yield, plant type, and fertility. Eight sterile or semi-sterile plants were discovered in 6 of 39 R4 lines. Our results suggest that multiple genetic changes have occurred in the tv somaclonal variant and while the original tv mutant is stably inherited, additional genetic abnormalities occur following sexual reproduction.
Six F1's involving 6 multiple genetic marker stocks and a common inbred parent (PU812) were cultured to study the genotypic effect on regeneration ability and frequency of somaclonal variation in R0 for the known heterozygous marker genes. Leaf discs 7 mm in diameter were excised from young fully expanded leaves of 6-7 week old plants, and cultured on MS medium supplemented with cytokinins (Kinetin, Benzyladenine) and IAA. With few exceptions, the parents and F1's responded similarly to different hormone combinations. The beat hormone combinations for shoot formation were 4 mg/l Kinetin + 0.5 mg/l IAA and 2.3 mg/l BA + 0-0.18 mg/l IAA.
Only 2 of the 6 multiple marker stocks and the common inbred parent (PU812) were successfully regenerated. Four of the six hybrids between PU812 and the multiple markers were readily regenerated, whereas 2 hybrids failed to regenerate with several different hormonal combinations. No mutations have been observed for the known heterozygous markers in 76 R0 tissue culture regenerants.
To find fertile garlic clones to be used in the cross breeding program, 213 accessions were subjected to cytological study at meiosis I. Most accessions (185 clones) showed abnormal chromosome configurations of ring of four, six or eight, which are ascribed to single or multiple translocations. Two clones showed asynaptic behavior forming 16 univalents from zygotene to metaphase I, and 26 clones revealed regular chromosome paring of 8 bivalents.
Only six of 26 clones showing normal meiosis produced viable pollen grains, while the rest were male sterile. From the segregation of crosses between male sterile and fertile clones, the male sterility is presumed to be governed by single recessive gene.
Hybrid plants between the fertile clones appeared, in general, intermediate of the parents in field performance.
Heterozygous multiple marker genetic stocks were synthesized by crossing three multiple genetic marker stocks to a common inbred parent PU812. The four parents and 3 F1's were cultured to obtain regenerants from leaf discs. Fifty four regenerants were derived from 3 F1's and 12 from the 4 parents, Among the regenerants, 16 plants were identified as tetraploid (24.2%); low fertility was usually associated with tetraploidy, however there were a few exceptions.
Selfed seeds, identified by cluster number, were harvested from sexual F1's and R0 plants for F2 progeny tests for the known marker genes. While there were no abnormal segregations for marker genes in the sexual progenies, 13 of 46 progenies from tissue culture derived regenerants showed significant deviations from expected normal segregations for a number of markers. Two of the abnormal progenies were identified as tetraploids by root-tip examinations; segregation ratios fit duplex random chromatid segregation for gene a on chromosome 11 and random chromosome segregation for gene c on chromosome 6. The cams of abnormal segregations in other progenies remain unknown. Results suggest that unknown genetic events arising during tissue culture may distort segregations for marker genes in the subsequent sexual progeny of tissue culture regenerants.