EFFECT OF SEVERITY OF DEFOLIATION ON THE VIABILITY OF REPRODUCTIVE AND VEGETATIVE AXILLARY BUDS OF TRIFOLIUM-REPENS L

This glasshouse experiment was performed to assess the effects of a ra nge of constant defoliation regimes applied to cuttings of a single la rge-leaved genotype of Trifolium repens L, on the viability of its axi llary buds. Plants were established to comprise a single main stolen ( axillary branches were removed) and defoliation treatments were applie d by removing the older (basal) leaves until leaf complements of 1.0, 1.5, 2.0, 2.5, 3.0 or all leaves (control) remained. Basal leaves were subsequently removed as necessary to maintain the target leaf complem ents. Only severe defoliation (leaf complements of 1.0 and 1.5) induce d a loss of viability in axillary buds. Loss of viability was greatest in reproductive buds present within the apical bud when the treatment s were first imposed. Although the most severe treatment (leaf complem ent 1.0) resulted in death of half the plants, in plants surviving tha t treatment, death of vegetative axillary buds was restricted to 21% o f the vegetative buds at the three youngest node positions within the apical bud at the lime of treatment application. No other treatment in duced any loss of viability of vegetative buds. There was no loss of v iability of axillary buds at nodes formed after the treatments were im posed. The frequency of initiation of inflorescences at nodes formed a fter treatments were imposed decreased as defoliation severity increas ed. Severe defoliation resulted in marked changes in plant morphology indicative of a sharp decrease in availability of intraplant resources . It was concluded that under severe defoliation: (1) the potential fo r vegetative growth (as represented by viable vegetative axillary buds ) was maintained at the expense of reproductive growth; and (2) that t he loss of viability of axillary buds was associated with the sudden c hanges in physiological processes induced by defoliation as there was no loss of viability in buds formed after plants had adjusted their ph enotype to one of smaller size. (C) 1996 Annals of Botany Company