Lesson 12: Crop Improvement and Seed

PLANT BREEDING

Science, art, and business of crop improvement for human benefit

PLANT BREEDING

Improves plant quality, disease, and insect resistance, change in maturity duration, agronomic characteristics, photosensitivity, synchronous maturity, non-shattering characteristics, etc.

Domestication

process of bringing wild species under human management

Germplasm collection

collection of a large number of genotypes of a crop species and its wild relatives

Introduction

taking a genotype or a group of genotypes of plants into new environments where they were not being grown before

Hybridization

The crossing of genetically dissimilar individuals to create new genetic combinations.

Hybrid

The offspring produced from hybridization.

Inbreeding

The mating of related individuals (same ancestry). leading to increased homozygosity.

Inbred

A homozygous line developed through continuous inbreeding.

Topcross

A cross between an inbred line and an open-pollinated variety (OPV).

Testcross

A cross between a plant/line and a tester. The tester may be an inbred, hybrid, synthetic, or OPV. Commonly used to evaluate combining ability or genotype performance

Backcross

A cross between a hybrid (F) and one of its parents

Polycross

Open poltination in isolation among selected genotypes Designed to promote random mating among the selected parents.

Reciprocal Cross

A cross between two individuals where: Each serves as the male parent in one cross And the female parent in the other. Used to detect maternal or cytoplasmic effects

Intraspecific Cross

Crossing individuals within the same species.

Wide (Distant) Cross

Crossing genetically distant or unrelated individuals, often from different species or genera.

Introgressive Hybridization

Repeated backcrossing of interspecific hybrids to one parent. Allows the transfer of specific genes from one species into another.

Heterosis or hybrid vigor

superiority of the F1 hybrid over its parents

Combining ability

the ability of a genotype to transfer its desirable traits to its progeny

General combining ability

average performance of a strain in a series of crosses

Specific combining ability

deviation from performance predicted on the basis of general combining ability of parent lines

Inbreeding depression

loss of vigor due to inbreeding

MUTATION

Heritable change in an organism

Spontaneous mutation

mutations occurring in natural populations

Induced mutation

mutations artificially produced by treatment with certain physical or chemical agents or mutagens

Chimera

an individual with one genotype in some of its parts and another genotype in other parts

Polyploidization

increasing ploidy level to more than two identical or distinct genomes

Natural Selection

Change in gene frequencies from one generation to another because of differences in survival and reproductive abilities of parent genotypes in natural populations

Artificial selection

change in gene frequencies brought about by man as is done in plant breeding where certain individuals or genotypes are not used as parent of the next generation

Stabilizing or normalizing selection

when adaptive individuals in the populations are selected under a constant environment through the years: keeps the population constant and eliminates the deviants; reduces the variability in the population

Directional selection

change towards a particular direction due to changing environments resulting in change of genetic contribution of the population; mode observed when breeders do artificial selection

Diversifying or disruptive selection

opposite of stabilizing selection; leads to either formation of subpopulations differing in their characteristics or polymorphism in which each genotype is represented by a distinct phenotype

Phenotypic variance

sum of genotypic variance, environmental variance and GE variance

Genotypic variance

sum of additive and non-additive types of gene action

Additive

due to individual effects of genes

Non-additive

due to intralocus and interlocus interactions

Environmental variance

effect of environment on the phenotype and estimated by measuring variation in a genotypically uniform population growth in a certain location

GE interaction

change in ranking and/or performance of genotypes when grown in different environments: estimated by computing variances of genotypes when grown in a number of locations which are environmentally diverse.

EVALUATION

Assessment of the performance of newly developed lines of a crop through appropriate multi location trials and tests

Observational yield test

may test separate groups of experimental lines; uses incomplete block design or triple lattice design with 2 to 3 replications in one location

Preliminary yield test

evaluation including a check variety using incomplete block design with 2 to 3 replications in at least 2 locations

General yield test

uses randomized complete block design with 3 replications in at least 3 locations

Advanced yield test

elite lines from general yield tests evaluated using randomized complete block design with 4 replications in 6 to 10 locations

stock seed

is known as breeder seed once the identified strain is released and notified.

Seed production

proper isolation procedure is necessary to maintain the genetic purity of the variety

Isolation

separation of a population of plants from other genotypes with which they are capable of mating

Seed processing

drying, cleaning and grading, testing, treating, bagging and labeling of seed

Hybrid

first generation offspring of a cross between two individuals differing in one or more genes

Synthetics

seed mixture of strains, clones, inbreds or hybrids, maintained by open pollination for a specified number of generations; the component units are propagated and the synthetic reconstituted at regular intervals

Composites

mixture of genotypes from several sources, maintained by normal pollination

Inbreds

purelines originating from self-pollination and selection

Multilines

blends; composite of isolines

Isolines

Lines that are genetically similar except for one gene

Open pollinated variety

variety maintained through natural cross pollination

Landraces

farmer-selected cultivated forms

3 line system

male sterile line (A), maintainer line (B) and restorer line (R)

2 line system

male sterile line, the expression of which is influenced by environment and any inbred variety as pollen parent

1 line system

use of apomixes to produce the F1 seeds and maintain the genotype of the F1

Breeder seed

controlled by the originating plant breeder: starting point of all subsequent classes of seed: seeds obtained from uniform panicles by breeders: 100% pure

Foundation seed

seed produced from breeder seeds: source of registered and/or certified seeds: carries a red tag

Registered seed

produced from foundation or registered seeds and carries a green tag

Certified seed

produced from foundation, registered, or certified seeds and carries a blue tag

Good seed

produced from varieties not yet approved by NSIC

Germplasm

the sum total of hereditary material or genes present in a species

Plant germplasm

genetic source material used by plant breeders to develop new cultivars