Plant Breeding, Seed Technology and Genetics
Plant Breeding, Seed Technology and Genetics
This domain tests Mendelian inheritance, breeding methods, variety development and seed production. Expect questions on self- and cross-pollinated crops, hybridization, seed classes, genetic purity and germination.
Core rules
- A monohybrid cross gives 3:1 phenotypic and 1:2:1 genotypic ratios in F2; a testcross against the recessive parent gives 1:1.
- Self-pollinated crops are improved by pureline selection and pedigree breeding; cross-pollinated crops often use mass selection, recurrent selection and hybrid seed production.
- Seed classes in certification are nucleus, breeder, foundation and certified seed; truthfully labelled seed is a separate category.
- Pure live seed (PLS) = pure seed fraction x germination fraction. Isolation distance protects genetic purity from cross-pollination and contamination.
Worked example
Certified seed required for 20 ha at 100 kg/ha plus 10% extra = 20 x 100 x 1.10 = 2,200 kg. If pure seed is 98% and germination 90%, PLS = 0.98 x 0.90 = 0.882 = 88.2%. To deliver the same live seed, adjusted rate = 100/0.882 = 113.4 kg/ha; for 20 ha plus 10% = 20 x 113.4 x 1.10 = 2,495 kg. The reasoning is that inert matter and dead seed must be compensated by sowing more material.
Traps
Genotype is genetic constitution; phenotype is observable expression. F1 is uniform in a pure-line cross, but F2 segregates. Seed certification is not the same as seed testing. Do not ignore PLS when a tag gives low germination. Isolation distance depends on crop and seed class.