Agricultural Science 2021 Jamb Examination

Gmelina arborea is a fast-growing hardwood tree species widely cultivated for pulpwood production.
It is preferred because of its straight stem, rapid growth rate, and high cellulose content, making it ideal for paper manufacturing.
Other species like Cassia, Alibiza, and Tectona are mainly used for timber and furniture rather than pulpwood production.

Callosobruchus maculatus, commonly known as the cowpea weevil, is a major storage pest of cowpea.
The adult beetle lays eggs on cowpea seeds, and the larvae burrow into them, reducing their quality and viability.
It rarely attacks cereals such as maize, rice, or millet, making cowpea its specific host.

Gummosis is a fungal disease in citrus caused primarily by *Phytophthora* species.
The infection causes the exudation of a gummy substance from cracks on the bark of the trunk and branches.
It is favoured by poor drainage and high soil moisture, distinguishing it from bacterial or insect-related diseases.

Tridax procumbens, commonly known as Tridax, produces light seeds with hairy structures (pappus) that allow them to be carried easily by the wind.
This adaptation enhances its wide dispersal.
Other weeds like Boerhavia diffusa and Acanthospermum hispidum rely on other means such as animal attachment or mechanical dispersal.

Mosaic disease is caused by viruses that affect the chlorophyll of leaves, leading to mottled or patchy discolouration.
The symptoms appear as alternating light and dark green areas, giving a mosaic-like pattern.
It rarely affects roots, stems, or fruits directly, which makes the leaves the main part showing visible symptoms.

Crop improvement typically begins with the introduction of new plant varieties from different regions.
These introduced species are evaluated, and desirable ones are selected for further improvement.
Finally, breeding is conducted to combine favourable traits.
Therefore, the sequence is Introduction → Selection → Breeding.

Recessiveness is the condition in which an allele’s effect is masked by the presence of a dominant allele in a heterozygous individual.
The recessive trait only appears when both alleles are recessive.
This concept explains why certain genetic traits skip generations or remain hidden.

Total pests = 100
25% died → \( 25/100 \times 100 = 25 \)
Remaining = \( 100 - 25 = 75 \)
40% of the remaining sent for examination → \( 40/100 \times 75 = 30 \)
Remaining pests = \( 75 - 30 = 45 \)
Hence, the number of pests left on the farm is 45.

Total feed consumed = 25 kg by 200 layers.
Feed consumed per layer per day = \( \dfrac{25}{200} = 0.125 \; \text{kg/day} \).
This means each layer consumes 125 g of feed per day, which is within the standard feeding rate for layers.

Salvage value = Initial cost − Depreciation value\[ 50,000 - 10,580 = 39,420 \]Therefore, after one year of use, the tractor’s salvage value is ₦39,420.