Ontogeny of elephant grass and the influence of defoliation on stem elongation of basal and aerial tillers

Abstract

The plant morphological development comprises a sequence of interactive events within and between interconnected phytomers, which defines its morphogenetic characteristics. As a consequence, the stem elongation process is probably integrated with other features of plant growth and development. In order to identify morphological markers (number of accumulated phytomers in the plant - Lk - or sward leaf area index), that could be associated with the beginning of stem elongation, to evaluate the effect of defoliation on the plant's ontogenetic programme and if there are differences in the rhythm of growth or in the factors triggering stem elongation in basal and aerial tillers, an experimental protocol for studying isolated plants specifically designed for this purpose. Two experiments will be carried out with Pennisetum purpureum Schum. cv. Napier (elephant grass). The first experiment aims at characterizing the regulation of the stem elongation process according to plant's ontogenetic programming for both basal and aerial tillers throughout the year: summer (January to March 2015), autumn (April to June 2015) and spring (October to December 2015). The second experiment will be carried out during summer 2016 (January to March) to evaluate if and how defoliation affects the ontogenetic programming and the stem elongation process in elephant grass. Treatments will correspond to three severities of defoliation (removal of 25, 50 e 75% of pseudostem length) plus a control (non-defoliation), and will be assigned to experimental units according to a complete randomised block design, with four replications. Plants will be harvested for evaluation every time they reach the Lk value defined in the first experiment. From this experiment, we expect to understand what are the morphological characteristics involved and how they operate to modulate stem elongation in tussock forming grasses. This knowledge is essential to define grazing management strategies compatible with the morphological plasticity of plants and capable of maximizing herbage production without jeopardizing plant community stability. (AU)