Diallel analysis of varying late season night temperatures on the development of a range of fluecured tobacco (Nicotiana tabacum l.) genotypes : a thesis presented in partial fulfillment of the requirements for the degree of Masterate of Agricultural Science in Plant Science at Massey University
A study was conducted in the climate room facilities, at D.S.I.R. Plant Physiology Division, Palmerston North, on the effect of varying late season night temperatures on the development of a range of flue-cured tobacco genotypes. The study involved imposing three night temperatures, 10°C, 15°C and 20°C, when the plants came into flower. Ten F1 genotypes of a five parent diallel cross (no parents, no reciprocals) were grown at each night temperature with three replications per temperature. Fourteen morphological, physical and chemical characters were measured. The effect of late season night temperature was negligible but there was some evidence of genotype environment interaction for some of the characters. The experiment was conducted using single plants as plots and the statistical analysis showed acceptable coefficients of variation for biological studies. The genetic analysis of the diallel showed that general combining ability variance is the most important type of genetic variance in the characters examined. This agrees with the majority of other tobacco diallel studies. As general combining ability variance is largely a measure of additive genetic variance, breeding homozygous lines from a heterozygous base population should be the best approach to follow. Heritability values were of sufficient size for several of the commercially important characters to indicate that improvement through selection was possible. General combining ability and phenotypic simple correlations between pairs of characters were generally in good agreement, demonstrating that phenotypic selection will result in altering the genotypes in the desired direction for the characters in question. The experiment showed a large negative correlation between the two economically important characters, yield and total nicotine alkaloids. This result is in agreement with similar studies carried out by other workers in this field. The experiment revealed a number of improvements which could be useful in the conduct of future tobacco climate room studies.