Plant Sciences
ASRB NET Plant Sciences integrates agronomy, genetics and plant breeding, plant pathology, entomology, horticulture and plant physiology. Questions test whether you can connect crop management with genetic and physiological explanations rather than recall isolated definitions.
Core concepts
- Agronomy: yield is a function of components such as ears per m², grains per ear and grain weight; the first component usually has the largest compensatory effect.
- Genetics: qualitative traits follow Mendelian ratios; quantitative traits are polygenic and analysed through variance components and heritability.
- Plant pathology: the disease triangle requires a susceptible host, virulent pathogen and favourable environment; management removes at least one leg.
- Entomology: economic threshold level (ETL) triggers control before the economic injury level (EIL) is reached.
- Horticulture: propagation by seed, cutting, grafting, layering or tissue culture depends on species and clonal fidelity.
- Physiology: photosynthesis, water potential and source–sink relationships explain yield responses to light, water and nutrients.
Worked example
A pure-line cross between tall purple-flowered and dwarf white-flowered peas gives F1 all tall purple. Selfing F1 gives F2. Assuming independent assortment and complete dominance, the expected F2 phenotypic ratio is 9 tall purple : 3 tall white : 3 dwarf purple : 1 dwarf white. Reasoning: two monohybrid 3:1 ratios multiply to 9:3:3:1. A deviation in a small sample is tested by chi-square, not by changing the expected ratio.
Traps that cost marks
- Treating heritability as a fixed property of a trait; it is population- and environment-specific.
- Using ETL as an eradication target; it is an action threshold.
- Confusing disease incidence, the proportion of plants affected, with severity, the area damaged.
- Applying a single propagation method across horticultural crops without considering juvenility or graft compatibility.