Genetic analysis of tetraploid and hexaploid wheat by utilization of monopentaploid hybrids.

This report deals with a method of analysis which uses existing hexaploid wheat monosomics to establish gene-chromosome associations in a tetraploid variety. Monosomics of Triticum aestivum cv. Chinese Spring belonging to the 14 lines of A and B genomes were crossed as female parents with Triticum durum cv. Capeiti, a spring type at present widely grown in Italy. For each line, two F 1 populations were obtained, normal pentaploids (2 n = 35) and monopentaploid (2 n = 34), in which, in turn, the monosomic A or B chromosome present was supplied by the tetraploid wheat. The morphological and physiological differences observed in the monopentaploid lines are attributed to differential expression of the genetic information concerning the character investigated, carried by the chromosome present in hemizygous condition. Then, only recessive or partially dominant alleles of the variety to be tested can be identified and attributed to a specific chromosome in the F 1 generation.Eight parameters were analyzed: culm and spike length, length and width of 1st (flag) and 2nd uppermost leaves, days from germination to heading and awn development.As far as culm length is concerned, although heterotic effect is present, seven chromosomes seem to be responsible for the modification of this character (1A, 2A, 2B, 3B, 4B, 5B, and 6 A); chromosomes 2A and 2B in particular, carry major factor (s) for plant height. A similar picture is presented by spike length which seems to be controlled by factors located in several chromosomes belonging to homoeologous groups 1, 2, 3 and 5, as well as the chromosome 4B.Leaf length, also, shows a complex pattern of inheritance. Monosomic conditions for chromosomes 1A and 1B increased, while monosomy for 5A and 5B significantly decreased, leaf length. A highly significant correlation was found between the mean lengths of the 1st and 2 nd leaves (= 0.74). Some monosomic lines (4A, 4B, 5A; 5B; 6A; 7A and 7B) had leaves significantly narrower than in the control and only monosomic 2A had broader leaves. The period from germination to heading seems to be influenced by at least 6 chromosomes. Three monosomic lines are significantly earlier (mono 1A, 7A and 5B) and three (mono 5A, 2B and 7B) are significantly later than the hybrid control.Finally, 8 monosomic lines were found to interfere significantly with awn development. Three lines (mono 2A, 2B and 7A) show a decrease and 5 (mono 1B; 3A, 3B; 4B and 6B) show an increase in awn development. On the basis of evidence in the literature and our own results, it appears that this analysis fits previous results perfectly and actually adds to the picture two further awn-promoting factors, A9 and A10, located on the 7A and 1B chromosomes respectively.