Characterization and quantification of somaclonal variation in tomato (Lycopersicon esculentum Mill.)
Abstract
The tangerine-virescent (tv) somaclonal variant, reported to be a single gene mutation exhibits several additional differences from its donor parent UC82B. Changes in earliness, fertility, growth habit, fruit size and shape, soluble solids and chlorophyll content, and loss of resistance to Verticillium wilt differentiate it from UC82B. F1 hybrids heterozygous for as many as 10 well described single gene markers were employed to estimate mutation frequency during tissue culture regeneration. No regenerants homozygous for the recessive markers were recovered from 853 F1 regenerants. The frequency of single gene mutation or mitotic crossing-over from the tissue culture protocols employed was estimated to be less than 1 $\times$ 10$\sp{-4}$ for the heterozygous loci examined. Tetraploidy proved to be a major source of somaclonal variation (9-10%); frequency varied widely among genotypes. Substantial numbers of chimeric plants (3.4%) were also recovered, however none appeared to represent chimeras for the heterozygous marker genes. Four of 5 sexual progenies from chimeric plants gave unexpected segregations for one of the marker genes; the fifth chimeric plant yielded a lethal seedling condition which predominated in seed from the first inflorescence but disappeared in seed from the third and subsequent inflorescences. Perturbed segregation for the known marker genes was observed in suspected diploid sexual progeny of F1 regenerants. Three regenerants gave progenies which showed duplex tetraploid segregation for the markers and were confirmed to be tetraploids by root-tip chromosome counts. Regenerants in which only one of the marker genes deviated significantly from the expected were observed. Also, several regenerants showed heterogeneity between inflorescences such that the data from different inflorescences could not be pooled. Highly significant deviations from expected diploid segregation occurred for approximately 4% of genes scored. One novel mutant was recovered in 152 sexual progenies. Polyploidy and chimerism appear to represent major causes for somaclonal variation in the tomato. Single gene mutations and mitotic crossing-over were substantially lower than previously reported. These results imply that multiple genetic changes characterize most somaclonal variants. The implications of these findings for the use of tissue culture in germplasm conservation and tomato improvement are discussed.
Degree
Ph.D.
Advisors
Tigchelaar, Purdue University.
Subject Area
Genetics|Plant propagation
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.