A diallel cross population was created from five clones that were randomly selected from five commercial cultivars of alfalfa (Medicago safiva L.). It was planted out at Edmonton and was studied for forage yield, vigor, growth habit, days to flower, plant height and frost tolerance in 1972 and 1973. Results showed that genetic difference between the five parents were large since the general combining ability (GCA) was more important than specific combining ability (SCA) and reciprocal effects (RE) for all the six characters. Greater genetic variance for forage yield, vigor, growth habit and plant height were observed in the second year of growth rather than in the year of establishment. Thus selection for these characters in the second year would be most effective. Genotype x environment interaction was significant for all characters and was relatively more important in the case of vigor and plant height. A study of the GCA effects showed that this source of variation was due to changes in the order of ranking for GCA effects over the environments. Genotypic correlation of the six characters revealed strong genetic association between forage yield, vigor, growth habit, plant height and frost tolerance in this population of alfalfa.
The combining abilities for leaflet size and specific leaf weight (SLW) were determined at two different stages of growth in a 7 ✕ 7 diallel cross population of alfalfa (Medicago sativa L.). Both characters were heritable since the general combining ability was larger than either the specific combining ability or the reciprocal effects. Greater genetic variance was observed at an early bud stage than at a late bloom stage. Large differences in SLW were obtained only at an early bud stage. Leaflet size and SLW were not correlated. Genotypes that combined larger leaflet size and higher SLW were identified. Thus both traits would respond to selection in a plant breeding program. The correlation of these characters with forage yield was generally poor.
The relative importance of general combining ability (GCA) and specific combining ability (SCA) in the year of establishment and in the following year were studied for forage yield, plant height, days to flower, growth habit, vigor, and frost tolerance in a diallel cross population of alfalfa (Medicago sativa L.). For both years GCA was more important than SCA for most of the characters. The ratio of GCA to SCA was generally greater for plants in their second year. There were marked differences in the GCA effects of the seven clones. Clones selected from adapted cultivars produced progenies that performed relatively well; those selected from unadapted cultivars gave progenies that were found to be generally inferior in forage yield, vigor, and frost tolerance. Both days to flower and vigor showed appreciable genotype ✕ environment interaction.
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