Efficient tissue culture and regeneration methods were established using immature wheat embryos as expiants. Genotype differences in culturability were evident, and from the ten accessions most amenable to culture, a total of 2,846 plants were regenerated. Extensive somaclonal variation for morphological and biochemical traits was observed among 142 regenerants of a Mexican breeding line, ‘Yaqui 50E’, and their progeny. Variant characters included height, awns, tiller number, grain colour, heading date, waxiness, glume colour, gliadin proteins and α-amylase regulation. The variant characters were heritable through two seed generations and included traits under both simple and quantitative genetic control. Segregation data suggested that mutations both from dominance to recessiveness, and from recessiveness to dominance, had occurred. Most mutations in the primary regenerants were in the heterozygous state but some were true-breeding and presumed to be homozygous. Chromosome loss or addition did not account for the variation and none of the variant phenotypes was observed in over 400 plants from the parental seed source. The distinctive parental gliadin pattern was maintained in the somaclones thus excluding seed contamination or cross-pollination as a source of the variation.

Heritable somaclonal variation in wheat

Triticale (×Triticosecale Wittmack) is the intergeneric hybrid between the female parent wheat (Triticum ssp.) and the male parent rye (Secale ssp.). The early work identifying and then producing primary and secondary triticales is described. Early wheat–rye hybrids were characterized by reproductive disorders and the cytology and meiotic characteristics have received much attention. Chromosome constitution has been studied particularly in relation to R-D substitution. Triticale has always been bred as a self-pollinating crop, although outcrossing can occur, and current cultivars are all nearly homozygous and homogeneous lines. Hybrid breeding (using cytoplasmic male sterility) makes the optimum exploitation of heterosis possible and, with the aid of molecular markers, triticale germplasm is presently being investigated to establish genetically diverse heterotic groups.The first released spring and winter cultivars were generally characterized by good disease resistance, but low grain yield, shrivelled grain, high protein content, excessive height, lodging and preharvest sprouting. Breeding effort has increased yield, reduced shrivelling and improved test weight but at the expense of protein content, which is now comparable to wheat and rye. Plant height and lodging are also now comparable to wheat and rye. Progress in reducing preharvest sprouting by genetic selection is proving difficult and slow. Triticale may be suitable for grain production and for dual purpose usage for forage and grain.The role of biotechnology in triticale improvement is described. The future of the crop, especially in low-input systems, and as raw material for industrial uses is considered.

The fortune of a botanical curiosity – Triticale: past, present and future

Plants derived from tissue cultures of six triticale genotypes were the subject of an analysis for changes in the rRNA genes located at the site of nucleolar organizer regions (the Nor loci) on chromosomes 1B, 6B and 1R. In addition whole plant phenotypes and the chromosomal constitutions of their progenies were examined for alterations. Following treatment of DNA with the restriction endonuclease Taq1, it was possible to assign electrophoretic bands representing rDNA spacer sequences to each of the chromosomes known to carry a major Nor locus. In general, the rRNA genes were found to be stable except in one family where a marked reduction in the number of rDNA units was observed. This reduction in 1R rDNA spacer sequences was heritable and correlated with reduced C-banding at the position of Nor-R1 on chromosome 1R. The change was clearly a consequence of tissue culture since six other plants regenerated from the same culture, and the original parent, did not carry the alteration.

Variation at the Nor loci in triticale derived from tissue culture

A variety of novel methods have been developed in recent years for the genetic modification of plant cells These include the techniques of protoplast and cytoplast fusion, uptake of cell organelles, and molecular techniques involving the uptake and integration of foreign DNA Each of these aspects is adequately-covered elsewhere in this volume

Regeneration of Plants from Single Cells of Cereals and Grasses

A procedure was established for the induction of regenerable calli from immature inflorescence segments of high-tannin cultivars of sorghum (Sorghum bicolor (L.) Moench). Murashige & Skoog's medium with several components altered was utilized for inducing, maintaining, and regenerating the cultures. Embryogenic calli formed at a frequency of 8–70% depending on the genotype. During a ten-month period, 3600 plants were regenerated from eight genotypes tested. Among the developmental stages of immature inflorescence tested (from differentiation of secondary branch primordia to floret formation) no critical differences were found in potential for callusing, embryogenesis or regeneration. Genotypic differences were observed in pigment production, embryogenic callus formation, shoot differentiation, and in maintenance of regeneration capacity.

W.A. Keller

Papers

Plant regeneration from inflorescence cultures of hexaploid triticale