Agricultural Science 2019 Jamb Examination

Rice blast is caused by the fungus *Magnaporthe oryzae*. It is one of the most destructive diseases of rice worldwide, affecting leaves, stems, and panicles. The fungus thrives in humid and warm conditions, producing lesions on leaves that can coalesce, leading to reduced photosynthesis and yield losses. Since the pathogen is fungal, it is neither viral, bacterial, nor due to nutrient deficiency.

Soil pH is a measure of acidity or alkalinity. A neutral soil has a pH of 7.0. When soil pH is greater than 7.0, it is considered alkaline, meaning it has excess hydroxyl ions (OH⁻) compared to hydrogen ions (H⁺). Soils with pH less than 7 are acidic, while soils around 6.0–7.0 are favorable for most crops. Therefore, a soil with pH > 7.0 is alkaline.

Rice is well known for its requirement of silicon for proper growth. Silicon strengthens cell walls, enhances resistance against lodging (falling over), and improves tolerance to pests and diseases. It also helps rice plants withstand environmental stresses such as drought and salinity. While silicon can benefit other crops, rice shows a particularly high demand for it compared to maize, groundnut, or green gram.

Phalaris minor, also known as little seed canary grass, is a problematic weed in wheat fields. It closely resembles wheat seedlings, which makes it difficult to identify and control in early growth stages. The weed competes with wheat for nutrients, light, and water, leading to significant yield losses. It is not commonly associated with maize, rice, or cotton cultivation.

Crop rotation refers to the practice of growing different crops sequentially on the same piece of land across seasons. For example, planting legumes after cereals improves soil fertility because legumes fix atmospheric nitrogen. This practice helps in breaking pest and disease cycles, improving soil structure, and maintaining nutrient balance. It is different from intercropping (growing multiple crops simultaneously) or strip cropping (growing crops in adjacent strips).

Rinderpest is a viral disease of cattle caused by a morbillivirus. Transmission primarily occurs through inhalation of aerosols containing the virus. Close contact between healthy and infected animals facilitates spread via respiratory secretions. While contaminated feed or water may play minor roles, airborne inhalation is the most significant mode of infection, leading to rapid outbreaks in herds.

Pox diseases in livestock, such as sheep pox, goat pox, and cowpox, are caused by poxviruses, which belong to the family *Poxviridae*. These viruses cause characteristic skin lesions (pustules and scabs) and can lead to economic losses in animal husbandry. They are not bacterial, protozoan, or fungal in nature.

Calcium and phosphorus are essential minerals for eggshell formation. Calcium carbonate provides the primary structure of the shell, while phosphorus supports metabolic processes that ensure proper mineralization. Deficiency of either mineral leads to thin or soft-shelled eggs. Sodium and sulphur do not directly influence shell thickness in the same way.

Iodine is a critical component of the hormone thyroxine (sometimes spelled thyrozine), produced by the thyroid gland. This hormone regulates metabolism, growth, and development in animals. Deficiency of iodine leads to goiter and reduced metabolic efficiency. It is not involved in the production of oxygen, insulin, or progesterone.

In sheep, the act of mating is specifically referred to as 'tupping'. This term is commonly used in sheep husbandry to describe the process of a ram mating with ewes. The term differs from other livestock such as poultry (treading) or general animal breeding (servicing). 'Courting' is a behavioral interaction but not the technical term for the mating process in sheep.