GROWTH RESPONSE OF THREE INDIGENOUS TREE SPECIES TO HORMONE AND SALT STRESS IN SOKOTO NIGERIA

ABSTRACT 

Seeds of three forest tree species namely Acacia senegal (L.) Willd, Balanites aegyptiaca (L.) Delile and Parkia biglobosa (Jacq.) were used to investigate the effect of different salinity (NaCl) and auxin (IAA) concentrations on germination percentage, stem height growth, collar diameter study and Relative Growth Rate (RGR). A factorial experiment in a completely randomised design was employed. 90 seedlings of the tree species were randomly divided into six treatment groups of 3 seedlings with five replicates. The experimental hormone at three levels of (0.0, 2.77 and 3.62μgg-1) and salt at two levels (2.2 and 2.8dSm-1) concentrations were respectively administered to each treatment for a period of twelve weeks. Result showed that seedlings administered with salt concentrations of 2.2dSm-1 and 2.8dSm-1 showed decrease in germination percentage, stem height growth, collar diameter and Relative Growth Rate. Similarly, results showed that increasing concentration of NaCl reduced germination percentage, stem height growth and collar diameter in the species. Auxin (IAA) decreased seed germination percentage in Acacia senegal (12%) and Parkia biglobosa (6%) at 2.8dSm-1, but increased seed germination in Balanites aegyptiaca (4%) at both levels tested, just as stem growth and collar diameter of the species were also influenced. Balanites aegyptiaca showed high seed germination percentage, stem height growth and collar diameter in comparison to other species studied. Treatment combination 0μgg-1/2.8dSm-1 was observed to be best for the growth of Acacia senegal, 2.77μgg-1/2.8dSm-1 for Balanites aegyptiaca and 2.77μgg-1/ 2.2dSm-1 for Parkia biglobosa. Parkia biglobosa was very susceptible to salt stress. These results showed that salinity is a major abiotic factor that influence auxin production and distribution, nutrient assimilation and shoot growth in the species tested. Parkia biglobosa should not be used in regeneration on high saline soils.

CHAPTER ONE

INTRODUCTION

1.1    Background of the Study

Marginal lands sometimes called wastelands or idle lands can be defined as lands which are of no importance for biodiversity or carbon sequestration. They play no role in food production and in guaranteeing people’s livelihood (Salva, 2008). It has been discovered that they have poor soil containing toxic levels of salt and are deficient in essential plant nutrients. They are generally unsuitable to crops. High concentration of salt particularly in the root zone could cause stress to a plant and eventually damage or kill it. Salt stress often coexist with other abiotic stresses such as drought. Tilman et. al. (2006) estimated that developing countries have vast area of marginal lands (at least 500 million hectares). Genetic analysis has shown that tolerance for abiotic stresses such as salinity could be attributed to germplasm – hormones (Mackill, 2004).

Plant growth has been determined at different levels to involve different metabolic processes in cells and there is a link between the cells and some external factors. Philipson (1987) showed how flowering could be induced in potted grafts of Sitka spruce and hybrid larch species by stem injections of a mixture of gibberellic acid (GA4/7 – a hormone) in combination with drought and high temperature treatments (external factors). Differentiation processes were not controlled just by a single factor, but by a complex, balanced equilibrium of growth regulators and external factors like light, temperature, nutrients, moisture and soil. Researches have indicated that hormones mediate between an external factor and physiological activities (Benjamins and Scheres, 2008; Zhang et al. 2000; Zhu, 2000). The process of tree breeding techniques has advanced and is currently at the phase where certain economic traits such as high wood density…