Somaclonal variation in the progeny of plants regenerated from callus cultures of seven inbred lines of maize

Abstract

Callus cultures were initiated from immature embryos of three dent corn inbred lines: FR27rhm (B73 derivative), 79-R4443, and EXL1; and four sweet corn (sh-2) inbred lines: f84-267, f84-275, f84-278, and f84-700. Extensive qualitative variation was noted in self-pollinated progeny of plants regenerated from callus of FR27rhm, EXL1, and f84-700; quantitative variation was measured in self-pollinated progeny of plants regenerated from cultures of almost all inbreds. Most qualitative mutations were visible in the first self-pollinated generation; chimerism in regenerated plants was indicated by initial segregation of some mutants after two self-pollinations. All culture-induced mutant phenotypes were similar to known spontaneous mutations in maize; preliminary data indicate most have single-gene recessive inheritance. For qualitative variation, average mutation frequencies per regenerated plant were calculated as 0.18, 0.71, and 0.64 for FR27rhm, EXL1, and f84-700, respectively. Differences in mutation frequency among the four sweet corn lines were determined to have a genetic basis. Significant quantitative variation included alterations in date of pollen shed and silk emergence, silk emergence relative to pollen shed, plant height, ear, and kernel characteristics. These results show genotypic differences in the extent of qualitative somaclonal variation, with some quantitative variation having possible applications for conventional corn breeding programs.

Selection of regenerable maize callus cultures resistant to 5-methyl-DL-tryptophan, S-2-aminoethyl-L-cysteine and high levels of L-lysine plus L-threonine

“…The apparent anomaly in these data can be explained by hypothesizing that the R0 plants were either heterozygous for the resistance trait as indicated by the F~ cross or they were chimeric with the gene for resistance present in only the tassel or ear. Such chimerism in regenerated plants has been reported previously [19]. a Basal medium was D medium [4].…”

“…e Resistant plant regenerated from V 6 callus. culture was three years old at time of plant regeneration, so the chromosomal abberations [summarized in 15] and somaclonal variation [19] typically associated with old cultures may have contributed to the sterility of the regenerated plants. The elevated tryptophan and/or phenylalanine level may have also had an effect on the fertility of these plants, as suggested by Wasaka & Widholm for rice [16].…”

Genetic instability of plant tissue cultures: breakdown of normal controls.

“…(19,20), but a direct association between an active transposable element and a phenotypic mutant has not yet been demonstrated. Quantitative trait variation has also been observed by several researchers (21)(22)(23)(24). While this type of variant is somewhat more subtle than single-gene phenotypic mutants, it arises at least as frequently.…”

Tissue culture-induced DNA methylation variation in maize.

“…In maize this mutagenesis is manifested as qualitative mutations (6-11, t), quantitative trait variation (11)(12)(13), cytological abnormalities usually resulting from chromosome breakage (14)(15)(16)(17)(18)(19), and the activation of transposable elements (20-22, *, §). A hypothesis to explain the underlying basis of tissue culture-induced mutagenesis must contain mechanisms to explain the high frequency of all ofthe above types of variation.…”