[en] Station yield trial: Three high yielding mutants (8, 48, and EFM92) with better and stable performance were developed in our breeding programme and submitted for registration to the Agricultural Research Center (ARC), Egyptian Ministry of Agriculture and Land Reclamation. Multi-location yield trials indicated that mutant line EFM92 ranked first in all locations; significant yield increases recorded for it ranged from 14.7 to 74.0% over the check variety. Moreover, it was 15-20 days earlier than the check and/or other mutants. Mutant lines 8 and 48 produced higher seed yields than the check at two different locations. These mutants can probably be grown and produce more yield than the check variety at the low yielding environments. Seed quality assay: During 1996 and 1997, 15 promising lines of sesame including mutants and hybrid populations as well as the local variety were evaluated for seed protein, oil content and fatty acid composition. The protein content varied from 20.6 to 26.7%; hybrid population EXM90 gave the highest value. About 85% of the total fatty acids in the oil are unsaturated (oleic and linoleic) and 15% saturated, mainly palmitic and stearic. Linoleic acid ranged from 41.8 to 47.9%. Mutant lines 6, 9, and EFM92, which gave high oil content (54-55.5%) together with high linoleic acid values (45.2-47.8%), are recommended for breeding for seed oil quality. Heterosis, combining ability and type of gene action in sesame: A half diallel set of crosses involving seven parents was used to study heterosis and combining ability in the F₁ generation as well as the nature of gene action controlling seed yield and its contributing traits in both F₁ and F₂ in order to identify the most efficient breeding methods leading to rapid genetic improvement. The expressions of heterosis varied with the crosses and characters investigated. The maximal significant positive useful heterosis was observed for branches/plant (52.9%) followed by seed yield/plant (38%), capsules/plant (33.6%), capsule length (19.0%), 100-seed weight (18.6%) and plant height (12.1%). Analysis of variance for combining ability indicated that general (GCA) and specific (SCA) combining ability variances were highly significant for all studied traits. Estimates of GCA effects showed that EXM90, EFM92 and Mutant 8 were the best general combiners for earliness; the variety Giza 32 and Mutant 48 the best for seed yield and number of capsules per plant. Both parents and their derived crosses could be utilized for hybrid sesame production and varietal improvement in terms of the probability of selecting desirable segregants for yield and yield components. Estimates of the type of gene action confirmed the importance of both additive and non-additive (dominant) gene effects in the inheritance of the studied characters in both F₁ and F₂ generations. However the dominance components were larger than the additive ones for most investigated traits in the F₁ and vice versa in the F₂. Overdominance was also noted. Heritability in narrow sense (H_n) was low for most characters in the F₁. On the other hand, high values of heritability (H_n) were recorded for all the investigated traits in the F₂, indicating that the genetic variance associated with those traits was mostly due to additive effects of genes, and therefore, it could be concluded that selection based on the accumulation of additive effects would be very successful in improving such traits. (author)