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Analysis of seed production traits in interspecific hybrids between Trifolium repens (white clover) and Trifolium uniflorum : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Breeding and Genetics at Massey University, Palmerston North, New Zealand
Trifolium repens L. (white clover) is an important component of New Zealand’s pastoral and herbage seed industries. It has delicate shallow roots vulnerable to drought and pest attack. T. uniflorum is a wild species, adapted to dry environments, with deep woody roots but poor vegetative growth and only 1-3 florets per head. Hybridization was done to incorporate the drought tolerance and root characteristics of T. uniflorum into white clover. The primary hybrids (F1 and BC1F1) showed poor seed production. The project aimed to analyse this problem and improve seed production by further hybridization and selection.
The hybrids expressed high variation for almost all seed production traits. Heads per plant, florets per head and seeds per floret were important determinants with moderate to high heritabilities. The derived traits seeds per head, florets per plant and seeds per plant expressed low-moderate to moderate heritabilities. Flowering pattern showed high heritability. No negative correlations between seed production and root traits were found. Whereas nodes per stolon favoured head production, stolon production had a negative effect on nodes per stolon. No negative associations between head production, persistence and foliage production of the hybrids were observed. No cytoplasmic influences were evident.
The hybrids showed, higher self fertility and a wider gap between potential and actual seed yield than white clover. The BC1F1 generation produced low numbers of heads per plant and seeds per floret. Intercrossing coupled with recurrent selection improved variation, fertility and realization of potential seed yield. The second backcrossed and intercrossed generations had high seeds per floret and plant. Backcrossing of selected hybrids effectively recovered the white clover phenotype and created new variation. The BC2F1 and BC3F1 generations expressed the better head production ability of T. uniflorum combined with the bigger head size of white clover.
Seed production capability of the hybrids was successfully restored. More genetic variation was created in the hybrids for future breeding and selection endeavours.