ASRB NET key terms

The average performance of a parent line when crossed with a broad set of other lines, estimated from line-by-tester trials. It reflects mostly additive gene effects and guides selection of parents for hybrid development.

The deviation of a particular cross from what its parents' general combining abilities predict. It captures non-additive effects such as dominance and is used to identify the best specific hybrid combinations.

A mating design in which several female lines are crossed to a small number of common testers to estimate combining abilities and gene action. It is efficient for screening many lines with few crosses.

A maternally inherited condition in which mitochondrial genes prevent viable pollen formation, allowing hybrid seed production without emasculation. Fertility is restored by nuclear restorer genes in the male parent.

A nuclear gene that suppresses cytoplasmic male sterility and restores normal pollen fertility in the hybrid progeny. Its presence determines whether a CMS-based hybrid can set seed normally.

The differential response of genotypes across environments, so that ranking of varieties changes with location or season. It is analysed through stability models and multi-location trials before variety release.

The proportion of total phenotypic variation in a population that is due to genetic differences. In the broad sense it includes all genetic variance; in the narrow sense only additive variance, which predicts selection response.

The expected genetic gain per generation from selection, computed as selection intensity times narrow-sense heritability times phenotypic standard deviation. It predicts how fast a breeding population will improve.

Four criteria used to prove that a microorganism causes a disease: it must be found in diseased hosts, isolated in pure culture, reproduce disease when inoculated, and be re-isolated from the new lesions.

The inherent ability of a plant genotype to limit damage by a pathogen or pest through physical or chemical defence mechanisms. It may be complete, partial, or expressed only after infection.

The pest population density at which control measures should be applied to prevent the pest from reaching the economic injury level. It underpins integrated pest management decisions.

A decision framework that combines resistant varieties, biological control, cultural practices, and judicious pesticides to keep pest populations below economic thresholds while limiting environmental harm.

A scale expressing the soluble solids content of a liquid, mainly sugars, measured with a refractometer. It is used to judge maturity and quality of fruits, juices, and sugarcane.

The total acid content of a fruit or food sample, determined by titrating against a standard alkali and expressed as a named acid equivalent. It contributes to flavour balance with sugars.

The rate of increase in plant dry matter per unit leaf area per unit time. It measures photosynthetic efficiency of the canopy and is used in growth analysis of crops.

The total one-sided leaf area per unit ground area. It indicates canopy density and interception of light, and optimum values differ among crop species and growth stages.

The increase in crop dry weight per unit ground area per unit time, usually expressed in grams per square metre per day. It integrates leaf area and photosynthetic efficiency.

The amount of biomass or marketable yield produced per unit of water consumed, often expressed in kilograms per hectare per millimetre. It guides irrigation and drought-tolerance strategies.

A feed energy measure summing digestible crude protein, fibre, nitrogen-free extract, and 2.25 times digestible fat. It is widely used to formulate ruminant rations.

The energy in a feed remaining after subtracting faecal, urinary, and gaseous losses from gross energy. It is the energy actually available for maintenance and production in the animal.

The quantity of feed consumed by an animal after moisture is removed, expressed per day or as a percentage of body weight. It sets the ceiling on nutrient supply for production.

A prediction of the genetic merit of an animal for a trait, based on its own records and those of relatives, adjusted for known environmental effects. It is used to rank selection candidates.

A statistical method that estimates breeding values by simultaneously accounting for fixed effects such as herd, year, and sex and for random genetic relationships among animals. It is standard in national genetic evaluations.

A weighted linear combination of trait records or breeding values designed to maximise genetic progress towards an aggregate breeding objective. Weights reflect economic values of each trait.

A laboratory procedure that exposes an isolated bacterial culture to antibiotic discs or dilutions to determine which drugs inhibit growth. Results guide rational treatment and detect resistance.

The lowest concentration of an antimicrobial agent that visibly prevents growth of a bacterial isolate under standard conditions. It quantifies resistance and supports dose selection.

The total quantity of exchangeable cations a soil can hold on its clay and organic matter surfaces, expressed in centimoles of charge per kilogram. It indicates nutrient retention and buffering.

The proportion of the soil's cation exchange capacity occupied by basic cations such as calcium, magnesium, potassium, and sodium rather than acidic aluminium and hydrogen. It reflects soil fertility status.

The carbon held in soil organic matter, usually reported as a percentage or stock per hectare. It drives nutrient supply, aggregate stability, and water retention, and is a key carbon-sequestration metric.

The negative logarithm of hydrogen ion activity in the soil solution, measured in a specified soil-to-water suspension. It governs nutrient availability, microbial activity, and choice of crops and amendments.

The oven-dry mass of soil divided by its total volume including pore space, expressed in grams per cubic centimetre. It indicates compaction and is used to convert weight-based to volume-based values.

The water content remaining in a soil after free drainage has essentially ceased, usually a few days after thorough wetting. It marks the upper limit of plant-available water.

The soil water content at which plants can no longer extract water and remain wilted even in a humid atmosphere. The difference from field capacity defines available water capacity.

The horizontal force a tillage or traction implement must overcome to move through soil at a given depth and speed. It determines power needs, fuel use, and tractor-implement matching.

A splined shaft on a tractor that transmits engine power to implements such as rotary tillers and pumps at standardised speeds. PTO power ratings are used for implement selection.

Deciding when and how much water to apply, based on crop water demand, soil moisture status, and allowable depletion. Good scheduling maximises water use efficiency and avoids yield loss.

The ratio of the present value of benefits to the present value of costs of a project or technology. A ratio above one indicates that returns exceed costs at the chosen discount rate.

The sum of discounted future cash inflows minus outflows of an investment, using a chosen discount rate. A positive value indicates the investment adds value.

The discount rate at which an investment's net present value becomes zero. It is compared with the prevailing cost of capital to judge financial feasibility.

The standard deviation expressed as a percentage of the mean, allowing comparison of variability between data sets with different units or magnitudes. It is widely reported in field trial results.

A statistical procedure that partitions total variation in a data set into components attributable to specified sources such as treatments, blocks, and error. It tests whether treatment means differ significantly.

The standard deviation of a sample mean's sampling distribution, estimated as the sample standard deviation divided by the square root of sample size. It quantifies precision of an estimated mean.

The ratio of the vapour pressure of water in a food to that of pure water at the same temperature. It predicts microbial growth and chemical stability better than moisture content alone.

The time required at a given temperature to kill a specified proportion of microorganisms in a food under defined conditions. It underpins the design of sterilisation and pasteurisation processes.

An unbroken series of refrigerated storage and transport steps that keeps perishable food, vaccines, or biologicals within a specified temperature range from production to consumption.

A fish index calculated as body weight divided by length cubed, often multiplied by 100, indicating robustness or plumpness. It is used to assess fish health and feeding status.

The number or biomass of fish held per unit water volume or area in a culture system. Excessive density increases stress, disease risk, and waste loading, while low density wastes capacity.

The weight of feed consumed divided by the live weight gain produced over a period. Lower values indicate more efficient feed utilisation and lower production cost in aquaculture and livestock.

The amount of dissolved oxygen consumed by microorganisms while decomposing organic matter in a water sample over a set period, usually five days. It is a common index of organic pollution.

The oxygen equivalent of organic and oxidisable inorganic matter in water, measured by strong chemical oxidation. It is faster than BOD and indicates total pollutant load.

Nutrient enrichment of a water body, mainly by nitrogen and phosphorus, leading to algal blooms, oxygen depletion, and loss of aquatic life. Agricultural runoff is a major contributor.

Deliberate integration of trees or shrubs with crops and/or livestock on the same land unit, aiming to capture complementary resource use, diversify income, and improve soil and microclimate.