Showing papers by "International Maize and Wheat Improvement Center published in 1981"

Analysis of the rye chromosome constitution and the amount of telomeric heterochromatin in the widely and narrowly adapted hexaploid triticales.

Abstract: Investigations were made on the rye chromosome constitution and on the presence of telomeric heterochromatin in rye chromosomes of the 26 most widely and 24 most narrowly adapted triticale strains. Among widely adapted lines, 22 (85%) had a complete rye genome and four triticales only had chromosomal R-D genome substitutions. Twenty-three (96%) of the 24 most narrowly adapted triticales had substitutions between the chromosomes of the R and D genomes. The most widely adapted triticales accumulated fewer modified rye chromosomes in comparison to narrowly adapted lines. They had from one to three rye chromosomes with heterochromatic deletions: 46% of widely adapted lines had two modified rye chromosomes; 34% had three modified rye chromosomes, and 19% had a single modified rye chromosome. In widely adapted strains, the 1R, 4R, 5R and 6R modified chromosomes were observed; they were present in 80%, 73%, 50% and 11% of the cases, respectively. The most narrowly adapted triticales had from two to four modified rye chromosomes: 58% of the strains had three modified rye chromosomes; 29% had four modified rye chromosomes and 12% had two modified rye chromosomes. The modified 4R and 5R chromosomes were present in all of these lines. The 1R (modified), 6R (modified) and 7R (modified) were found in 83%, 25% and 16%, respectively, of the narrowly adapted strains.

Factors affecting reliability in age estimation in rural West Africa: a statistical analysis

Abstract: Ages of the same individual in two rounds of a rural survey in Sierra Leone spaced at intervals of six to ten months, were recorded by similar census-type methods, but using different enumerators. Substantial age differences were noted between the two surveys. Simple linear regression analysis was used to identify factors related to the interviewer, the interviewee and the method of interviewing that contributed to these age differences. It was concluded that age errors will be reduced by interviewing individuals directly rather than through a third party (usually the household head), more careful recruitment and training of enumerators and by the gradual spread of education and age awareness in rural areas.

Evaluation of an exotic maize population adapted to a locality.

Abstract: An exotic Zea mays L. population (‘Tuxpeno’) was adapted to North Carolina conditions by first introducing genes for adaptability from two North Carolina varieties ([(‘Jarvis’ X ‘Indian Chief’)‘Tuxpeno’]‘Tuxpeno’) including four generations of intermating, and then selecting for adaptability using maturity as the primary measure. The study evaluated selection for adaptability and the diversity available between adapted ‘Tuxpeno’ and the local varieties, ‘Jarvis’ and ‘Indian Chief’. Analytical procedures were developed to quantify the diversity between populations and the complementation of local varieties by introduced germ plasms. The analyses utilized the specific effects available from the diallel mating design. Three replicate selections responded similarly under simple recurrent mass selection (1/10) for the earliest disease-free plants initially and additionally for plant types (primarily height) in the final generation. The 1/4 local germ plasm permitted rapid adaptation of ‘Tuxpeno’ gene pool to local conditions. The adapted ‘Tuxpeno’ populations yielded similarly to the local populations with an average heterosis for grain yield of 28% when crossed to the local populations used as source of genes for adaptability. The diversity found between adapted ‘Tuxpeno’ lines and these local varieties based on genes affecting grain yield was 1.5 to 2.5 times that measured between the local varieties (‘Jarvis’ and ‘Indian Chief’). Diversity lost through intergradation with local material was a reasonable investment. Yield genes introduced from ‘Tuxpeno’ complemented local gene pools through nonadditive, primarily dominance-associated, gene effects. Reassortment of major gene blocks apparently occurred leading to significant divergence among replicate selections involving both additive-associated and dominance-associated gene effects.