DIALLEL CROSSES IN TRIFOLIUM MEDIUM

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Abstract
Seed-setting of the highly polyploid New Zealand zig-zag clover (T. medium) was improved by application of an arbitrary selection index (number of seeds per plant x percent fertile flowers). The top 8 plants from polycross tests were then diallel crossed and selfed, and the components of the resulting seed yield were recorded. Self-fertility was close to nil. Herbage production and flowering habits of the progeny were studied in replicated field trials. Heritability in the broad sense was high for seed number (83%), lower for fertility (46%) and intermediate for mean seed weight (57%). For mean seed yield, Wr, Vr graphs for 5 selfed progenies and their diallel showed marked differences in heterozygosity between the parents, and dominance of the parent with the heaviest seed. For herbage production, inbreeding depression ranged from 10 to 80%. Herbage production in the 8 x 8 diallel showed highly significant specific combining ability effects. These were also significant in vernalization requirement but not in date of flowering. General combining ability was much higher and highly significant for all 3 characters. For herbage production, heritability in the narrow sense, on a single plant basis, was higher (28%) than for date of flowering (14%).

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