Cotton ( Gossypium barbadence ) is the one of the most ancient important commercial crops next only to food grains and is the principal raw material for a flourshing textile industry.

 However, the production potential of the crop has been fully Exploited due to several factors. Biotic factors A biotic Microorganism factors Fungi

 the cotton crop suffers from many fungal disease.  foliar disease, seedborne and soilborne  Black mold,  alternaria wilt disease seedling  disease

 seedling disease complex of cotton, causes annual economic losses. the seedling disease complex is composed of several fungi which cause seriouse problems whatever cotton grown.the soil borne pathogens most commonly involoved in the seedlin disease complex in Egypt includines Rhizocotnia solani, and species of Fusarium, Pythium and Macrophomina sp.  fusaruim wilt and Verticilium wilt, there are the most imporatant disease of cotton probably causes greater economic losses in that crop in many different places in the world.

 the cotton growth and devlopment modle = dPp / dt  dPp = number of plants per mater dt = time the population models for cotton growth and development is composed of separate models for the population of indiviual plants,and each plant has a population of leaves (L), stems (S), roots, and fruits (number = F,mass = M )

 leaves Growth modle = ąL / ąt + ą L / ą a  ąL = no of leaves  ąt = plant at time  ą L = no of leaves in same age  ą a = plant at same age  Roots Growth modle = ąR / ąt + ą R / ą a  Stems Growth modle = ąS / ąt + ą S / ą a  Fruits Growth modle = ąF / ąt + ą F / ą a  Mass of pool modle = ąM / ąt + ą M / ą a

 Effect of verticillium or Fusarium wilt on plant growth and development  dФ s / dt =[( x pv x pv – 4.5  x10 -4 ) z ] / 100  dФ s = the percentage of plants showing foliar  symptoms  pv = inoculum density  z = pathotype severity (Gutierrez et al 1983)

 Estimating Yields loss  Y T = Y H (1- ∑ n i=1 ΔФ i )+ ∑ n i=1 y i ΔФ i  Y H =expected Yields of helthay in all plants  ΔФ i = plants becoming diseased  y i ΔФ i = Yields of diseased plants (Gutierrez et al 1983) ∑ 

 incidence and severity of symptoms on cotton  percentage plants with root disease index   1 = no of healthy seedling  2- 5 =no of browning to necrosis roots  6 = no of died plants

 Losses of crop = A / B X 100  A= Percent disease index  B = Percent disease over control  % increase in yield over control = C/ D X100 = kg pooled  C= Pooled yield ( kg /area ) in disease plant  D = Pooled yield ( kg /area )in plant over control (Chattannavar et al 2010)