add texture to tree(represented by spheres and cylinder) - opengl

Question

I'm rendering a tree using spheres and cylinders, and i use normal mapping to map bark texture
on the sphere and cylinder. Below is my vertex shader:
// Normal mapping light shader
// Vertex Shader
#version 130
// Incoming per vertex... position and normal
in vec4 vVertex;
in vec3 vNormal;
in vec4 vTexture0;
uniform mat4 mvpMatrix;
uniform mat4 mvMatrix;
uniform mat3 normalMatrix;
uniform vec3 vLightPosition;
// Color to fragment program
vec3 vEyeNormal;
smooth out vec3 vVaryingLightDir;
smooth out vec2 vTexCoords;
vec3 vTangent = vec3(1.0, 0.0, 0.0);
void main(void)
{
// Tangent Basis
vec3 b, t, v;
// Get surface normal in eye coordinates
vEyeNormal = normalMatrix * vNormal;
// Get vertex position in eye coordinates
vec4 vPosition4 = mvMatrix * vVertex;
vec3 vPosition3 = vPosition4.xyz / vPosition4.w;
// Get vector to light source
vVaryingLightDir = normalize(vLightPosition - vPosition3);
// Build Tangent Basis
t = normalize(normalMatrix * vTangent);
b = cross(vEyeNormal, t);
v.x = dot(vVaryingLightDir, t);
v.y = dot(vVaryingLightDir, b);
v.z = dot(vVaryingLightDir, vEyeNormal);
vVaryingLightDir = normalize(v);
// Pass along the texture coordinates
vTexCoords = vTexture0.st;
// Don't forget to transform the geometry!
gl_Position = mvpMatrix * vVertex;
}
And this is the fragment shader:
// Normal mapping light shader
// Fragment Shader
#version 130
uniform vec4 ambientColor;
uniform vec4 diffuseColor;
uniform sampler2D colorMap;
uniform sampler2D normalMap;
smooth in vec3 vVaryingLightDir;
smooth in vec2 vTexCoords;
out vec4 vFragColor;
void main(void)
{
vec3 vTextureNormal = texture2D(normalMap, vTexCoords).xyz;
vTextureNormal = (vTextureNormal - 0.5) * 2.0;
// Dot product gives us diffuse intensity
float diff = max(0.0, dot(normalize(vTextureNormal), normalize(vVaryingLightDir)));
// Multiply intensity by diffuse color, force alpha to 1.0
vFragColor = diff * diffuseColor;
// Add in ambient light
vFragColor += ambientColor;
vFragColor.rgb = min(vec3(1.0,1.0,1.0), vFragColor.rgb);
// Modulate in the texture
vFragColor *= texture(colorMap, vTexCoords);
}
But what i get is an ugly effect:
Can anybody tell me how i can make the bump mapping smooth?