A comparison of burley tobacco doubled-haploid lines with their source inbred cultivars.

A doubled-haploid line was randomly derived from each of seven burley tobacco, Nicotiana tabacum L., cultivars using anther culture and leaf-midvein chromosomal doubling. The doubled-haploid lines were compared to their source inbred cultivars in two experiments for several agronomic and chemical characters. A consistent relationship between anther-derived materials and reduced vigor was not observed in these doubled-haploid lines. Significant differences between the doubled-haploid mean and their source cultivar mean were observed only for days to flower and total alkaloids. The doubled-haploid means were not significantly different from their source cultivar means for yield, plant height, and leaf number. In total, 26 of the 35 individual comparisons between a doubled-haploid line and its source cultivar were nonsignificant. Reciprocal crosses between the doubled-haploid lines and their source inbred cultivars also demonstrated no significant differences. The diallel progeny of the seven doubled-haploid lines showed a similar genetic performance to that of diallel progeny from conventional materials in previous studies. The differences observed between the doubled-haploid lines and their source inbred cultivars could be explained by residual heterozygosity. The performances of the doubled-haploid progeny could also be attributed to the presence of residual heterozygosity in the original cultivars. As tested by reciprocal crosses, cytoplasmic effects were not significantly involved in the performance of the double-dhaploid lines.

Expressed resistance to black shank among tobacco callus cultures.

Quantitatively inherited resistance to the black shank pathogen (Phytophthora parasitica var. 'nicotianae') was expressed among callus tissue cultures of tobacco (Nicotiana). Tissue cultures of genotypes known to posses polygenic mechanisms for black shank resistance expressed that resistance in vitro when challenged by the viable pathogen. Callus of a susceptible cultivar was readily parasitized in culture. Furthermore, single gene resistance to the common pathogen race was also shown to operate in vitro. Nongenetic factors examined did not contribute significantly to the observed differences. Disease expression in vitro appeared to be highly correlated with its expression at the whole plant level.Screening for quantitative disease resistance can be complicated at the whole plant level by variable hostpathogen reactions and by significant genotype × environment interactions. Since quantitatively inherited mechanisms of black shank resistance are expressed in tobacco callus cultures, an in vitro host-pathogen system may be useful in screening tobacco lines for black shank resistance.

Genetic analysis of the anther-culture response of three spring wheat crosses.

Anther-culture response was examined among three spring wheat (Triticum aestivum L.) cultivars to evaluate the genetic component of response and to determine whether androgenetic performance could be improved by selection. The three lines, the three possible F1's among the three lines, their F2's, and the backcrosses to the parents were evaluated for callus production and regeneration capacity. Significant variation was observed among the generations of the three crosses for callus formation. Genetic variation for regenerability was nonsignificant. Callus production was negatively correlated (-0.24) with regeneration capacity. The random variation in the study was too great to determine whether major-gene differences for antherculture response exist among the three lines by examining population distributions. When the material was evaluated for quantitative gene effects, the estimates for the additive gene effects were generally greater than the estimates for the dominance gene effects for callus formation. Only the Pavon x Chris cross, however, exhibited a significant narrow sense heritability estimate for callusing response (0.94). Due to the large component of random variation and the varying selection potential among crosses for androgenetic performance, improving anther-culture response in wheat by selection could prove difficult unless the anther-culture process itself selects for response traits at the gametic level.