Theory question 103
Crop Diseases(a) Complete the table below: for maize smut and damping off of tomato, give the causal organism, one symptom and one preventive/control measure.
(b) State four ways in which each of the following factors affect crop production in West Africa (i) wind; (ii) light.
(c) Mention four human activities that promote deforestation.
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(a) Maize smut: fungus (Ustilago maydis); large galls on ears, tassels or stems that burst to release black powdery spores; resistant varieties, seed dressing, remove and burn infected plants, crop rotation.
Damping off of tomato: fungus (Pythium spp., also Rhizoctonia); seedling stems rot and become thin at soil level, seedlings collapse and die; sterilise nursery soil, avoid over-watering, good drainage, correct spacing, fungicides.
(b)(i) Wind (any four): increases transpiration and evaporation; helps pollination; disperses seeds and weed seeds; spreads pests and diseases; strong winds cause lodging and breakage; causes soil erosion.
(ii) Light (any four): supplies energy for photosynthesis; affects growth rate; daylength decides flowering of many crops (photoperiodism); affects ripening of fruits; causes phototropism; breaks dormancy of some seeds.
(c) Any four: logging/timber felling; mining and oil exploration; road construction; urbanisation and industrialisation; farming/shifting cultivation; estate and housing development; bush burning; fuelwood collection.
One organism, symptom and control for each disease.