Morphology of white clover during development from seed to clonal populations in grazed pastures

Abstract

Following germination, the ontogeny of white clover is characterized by two distinct morphological growth phases, a seminal taprooted stage followed by a clonal growth stage. Death of the seminal taproot and primary stolon initiates a process of fragmentation of the taprooted plant into a variable number of independent clonal fragments (plants) which comprise the initial population of the clonal growth stage. The objective of this study was to characterize the plant morphology of field-sown white clover populations from germination through to established clonal populations. Populations of eight white clover cultivars were assessed when sown with perennial ryegrass or tall fescue in pastures established under a common grazing regime for 16 months prior to imposition of continuous or rotational grazing treatments. One year from sowing, taprooted plants attained maximum size, with a mean plant branching order of 3·35, stolon DW of 460 mg and lateral spread of 250 mm, with some individuals having 6th order branching, 3·5 g stolon DW and 1m lateral spread. These taprooted plants were 4–5 times the size of plants in the subsequently formed clonal population. Nine months after sowing, the first individual taprooted plants fragmented into clonal plants. Twelve months from sowing, fragmentation processes were occurring at a linear rate, eliminating 6% of the original taprooted population each month. This resulted in a 12–15 month transition period when the white clover population comprised both taprooted and clonal plants. During this transition period, the initial clonal fragments produced from taprooted plants were large, and this maintained a larger mean plant size in the clonal plant proportion of the transition population than measured in the later fully clonal population. This process was also considered to act to prevent the development of the expected differences between grazing managements, as it was not until the third year when all taprooted plants had disappeared that the clonal populations developed characteristics reflecting the expected influence of grazing management. Variation due to white clover cultivar and companion grasses was minor. The substantial differences in plant size and branching structure between taprooted and clonal populations has significant implications for the evaluation of breeding lines.