(a) Discuss briefly the rosette disease of groundnut under the following headings: (i) causal organism: (ii) symptoms (iii) method of transmission; (iv) damage done (v) preventive and control measures. (b) Assuming the spacing of a g vegetable crop per stand is 30 cm x 30 cm, calculate the plant population expected in a portion of land measuring 60 m x 30 m
Explanation
(a) Rosette disease of groundnut discussed under: Causal organism: Virus Symptoms: (i) Infected plants shrink in size (ii) Leaves turn yellow with mosaic form of Mottling (iii) The leaves curl (iv) Plants become permanently stunted / retarded growth (v) Shortening of the internodes. Method of transmission: The causative virus is transmitted to plants by aphids and other piercing and sucking insects. Damage done: Reduction in size of leaves / curling of leaves - consequent reduction in photosynthetic area, resulting in very low yield, Preventive and control measures: (i)use resistant varieties (ii) use insecticides to destroy / control vector (aphids) (iii) adopt early planting. (iv) burn all infected plants / farm sanitation. (v) practice close spacing as a cultural method of control (b) Vegetable crop population calculation: Spacing for crop 30cm x 30cm = 0.3m x 0.3m :. Area of 1 stand of crop = 30cm x 30cm = 900cm² or x 0.3m =0.09m² Area of land (given) length = 60m width = 30m :. Area = (60 x 30)m². = 1800m² If a crop occupies an area of 0.09m², No of stand/crops of vegetable = 1800/0.09, or 18000000/900 = 20,000 crop stands
