Plant Improvement Flashcards
Trash heap method
have a pile of organic ‘trash’ near the village, like a compost pile
as the fruits and vegetables rotted, seeds matured and sprouted when conditions were favorable
What traits have improved throughout time
yield flavor seed retention upright growth habit ease of harvest resistance to pathogens tolerance of environmental conditions efficient utilization of nutrients
Important horticultural traits
quality traits
taste
color
storage quality
size and shape
Important horticultural traits
important for mechanical harvesting
uniform ripening
thicker shinned
resistant to bruising
Important horticultural traits
additional traits
flower shape, size, color, longevity
plant form, size, shape
folair characteristics, variegation, fall color, leaf retention
Variation
variation between individuals is the ‘raw ingredient’ for plant improvement
the basis for crop improvement is genetic variation
there is no basis for selection if all individuals are
Two factors of variation
environmental variation
genetic variation
Variation produces
new genetic combinations
desirable characteristics
Sources of new variation for plant improvement
recombination (meiosis)
spontaneous mutation
related species in plant families
germplasm collections
center of origin
where they evolved prior to domestication by man
gene
unit of inheritance
genes are encoded
by the sequences of bases
DNA is packaged in
chromosomes
chromosomes are contained in the
nucleus
information in genes is converted into / most genes encode
protein
proteins are responsible for carrying out
most of the essential functions in all organisms
different forms of the same gene are called
alleles
when both copies of a gene are the same in an individual are described as
homozygous
when two alleles of a gene are different in an individual are described as
heterozygous
differences between individuals in the sequences of bases in genes can be the source of
genetic variation
some alleles are deleterious and have negative effects
in humans cystic fibrosis, sickle cell anemia which are caused by genetic defects
most alleles of genes in plants do not have such drastic effects, red/pink/white flowers
genotype
genetic information
phenotype
appearance and performance
phenotype is determined by
genes and by the environment
some traits are controlled by
only one or two genes
qualitative inheritance
simply inherited traits
quantitative traits
traits are affected by the actions of many genes
Strategies for plant improvement
selection random mutations polyploidy plant breeding biotechnology
Selection
identification of desirable varieties in natural population
Two important points about selection of horticultural crops
selection is based on the utility of plants to the grower
selection is performed on a wider range of traits in horticultural crops
natural selection
evolution
in most cases, plants selected for agricultural purposes would not…
survive or be successful under conditions of natural selection
Sports (aka mutants)
sports are the result of rare spontaneous mutations in cultivated plants that result in new plants with desirable horticultural characteristics
examples of sports include
pink-fleshed grapefruit
seedless navel oranges
color variants of many apples
chimera
only one layer of tissue is altered
polyploidy
an organism has more than the normal diploid (2n) number of chromosomes
Why are polyploids useful?
polyploids tend to have larger cells, resulting in larger fruits, flowers, leaves
can be sterile “seedless” watermelon
plant breeding
deliberate hybridization of plants with complementary traits and selection of elite lines that combine these traits
Fundamental steps in plant breeding
- identify plants with complementary characteristics that can hybridize
- cross these 2 plants
- emasculate the female parent
- collect pollen from the male parent
- pollinate the female parent by hand - collect seed and grow progeny
- evaluate performance of the progeny in subsequent generations
- select the best progeny after evaluating their performance
- evaluation is carried out over several years and at many sites - propagation of improved variety
- production of seed or through asexual propagation - file for a ‘plant variety patent’
Hybrid vigor
cross, two different parents
plants are more vigorous, have a higher yield than inbred lines
F1 hybrids
Parent A (male) + Parent B (female) = F1 hybrid
Self-pollination
many crops are self-pollinated because they are not self-incompatible
grown as inbred lines
essentially all genes are homozygous
traits are stably inherited from generation to generation
breeding or new varieties requires the development and evaluation of new inbred lines
outcrossers
do not self pollinate
many horticultural crops are natural outcrossers
-some have biological barriers to self-fertilization (incompatibility)
gene introgression
new methods of biotechnology allow genes to be transferred from any species for plant improvement
Challenges of breeding
only 1 out of 16 of the progeny will contain the combination of those two genes necessary to express both traits
