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More Information on Introduction - Biotechnology and Traditional Plant Breeding

Plant Breeding: Overcoming the Species Barrier

In the early 1900s plant breeders began producing new crop varieties by cross breeding plants in different species and also different genera, the next level of genetic difference. This table provides selected examples of some of the crops with varieties that were developed using “wide crosses” and the traits transferred into that crop variety through the crosses.

 

Crop Species Trait Donor Species
Corn Fungal disease resistance Tripsacum dactyloides
Oats Increase yield 25-30% Arena sterilis
Beets Nematode resistance Beta procumbens
Tomato Virus resistance
Nematode resistance
Fungal disease resistance		 Lycopersicon peruvianum
Lycopersicon peruvianum
Lycopersicon impinellifolium
Rice Virus resistance Oryza nivora
Wheat Fungal disease resistance
Increase protein
Drought tolerance
Winter hardiness		 Aegilops squarrosa
Aegilops ovata
Agropyron elongatum
Secale cereale

Reference: Goodman, R.M., H. Hauptli, A. Crossway and V.C. Knauf. 1987. Gene transfer in crop improvement. Science 236: 48-54.

Laboratory techniques for crossbreeding plants that do not hybridize naturally


Barrier Techniques for Overcoming the Barrier
Pre-Fertilization Barriers
Failure of pollen germination Remove pistil then pollinate exposed end
Use recognition mentor pollen
Slow pollen tube growth Chemical treatment with organic solvents or growth regulators
Pollen tube growth stops In vitro fertilization
Use of plant growth hormones and chemicals like chloramphenicol and acriflavin
Failure to obtain sexual hybrids Protoplast fusion
Different # of chromosomes Chemically induce chromosome doubling
Post-Fertilization Barriers
Embryo abortion (immediate) In vivo/vitro embryo rescue/implantation
Embryo abortion-early stages of development Culture ovaries in petri dishes
Lethality of F1 hybrids Use cell culture to regenerate plants
Chromosome elimination Alter genomic ratios of species
Induce chromosomal exchanges with tissue culture or irradiation
Hybrid sterility Chemically induce chromosome doubling