NEWSLETTER ARTICLES

Franklin Laemmlen, Ph.D., County Director and Vegetables/Plant Pathology Advisor


From our Central Coast Agriculture Highlights newsletter -- June 2000 issue.

FOOD BIOTECHNOLOGY

Whether we agree or disagree with the technology, biotechnology is affecting or will affect our lives. Your quality of life may already have been affected. If you are a diabetic, you are probably using insulin that is being produced be a genetically engineered bacterium. Many of the cheeses we eat are made with chymosin, an rDNA-derived enzyme preparation. Some of the clothing you wear may be made from cotton that has been bred to resist insects and weed control products by genetic manipulation. The terms plant breeding, recombinant DNA technology, genetic engineering or genetic manipulation are now all being grouped under the term biotechnology.

Biotechnology has been in use ever since man discovered that he could change and/or improve certain plant or animal characteristics by breeding plants/animals with desirable characteristics with each other. Some of the resulting offspring of these crosses would hopefully carry the desired genes, which produce these traits in the next generation.

For years, the process of making new varieties of plants or breeds of animals has been a rather hit-and-miss affair, and scientists have searched for ways to improve the process. Through research, techniques have now been developed, which allow plant and animal breeders to identify and to select specific genes, which control traits and to transfer only those genes into a reproductive cell to produce new offspring.

A bewildering array of terms has come into being to help describe the process and science of gene transfer, which results in plants and animals with new characteristics. These terms are heard on the news or read in the paper, often with a minimum of explanation. The following paragraphs, and some future articles in this newsletter, will hopefully bring a better understanding to what you hear and read.

SOME USEFUL DEFINITIONS OF BIOTECHNOLOGY AND ITS COMPONENT TECHNOLOGIES

Biotechnology is any technique that uses living organisms or parts thereof to make or modify a product or improve plants, animals, or microorganisms for specific uses. All the characteristics of a given organism are encoded within its genetic material, which consists of the collection of deoxyribonucleic acid (DNA) molecules that exist in each cell of the organism. Higher organisms contain a specific set of linear DNA molecules called chromosomes, and a complete set of chromosomes in an organism comprises its genome. Most organisms have two sets of genomes, one having been received from each parent. Each genome is divided into a series of functional units, called genes, there being 20,000 to 25,000 such genes in typical crop plants like corn and soybean. The collection of traits displayed by any organism (phenotype) depends on the genes present in its genome (genotype). The appearance of any specific trait also will depend on many other factors, including whether the gene(s) responsible for the trait is turned on (expressed) or off, the specific cells within which the genes are expressed, and how the genes, their expression, and the gene products interact with environmental factors. The key components of modern biotechnology are as follows:

  • Genomics:The molecular characterization of all the genes and gene products of a species.
  • Bioinfomatics: The assembly of data from genomic analysis into accessible and usable forms.
  • Transformation: The introduction of single genes conferring potentially useful traits into plant, animal and microorganism species.
  • Molecular Breeding: The identification and evaluation of useful traits in breeding programs by the use of marker-assisted selection for plants, trees, animals, fish, and microorganisms.
  • Diagnostics: The more accurate and quicker identification of microorganisms by the use of new diagnostics based on molecular characterization of these organisms.
  • Vaccine Technology: Based on the use of modern immunology to develop recombinant DNA vaccines for improved disease control against lethal diseases.
In the 1970s, a series of complementary advances in the field of molecular biology provided scientists with the ability to readily move DNA between more distantly related organisms. Today, this recombinant DNA technology has reached a stage where scientists can take a piece of DNA containing one or more specific genes from nearly any organism, including plants, animals, bacteria, or viruses, and introduce it into a specific plant or animal species. The application of recombinant DNA technology frequently has been referred to as genetic engineering. An organism that has been modified, or transformed, using modern techniques of genetic exchange, is commonly referred to as a genetically-modified organism (GMO). However, the offspring of any traditional cross between two organisms also are "genetically - modified" relative to the genotype of either of the contributing parents. Plants that have been genetically modified using recombinant DNA technology to introduce a gene from either the same or a different species also are known as transgenic plants, and the specific gene transferred is known as a transgene. Not all GMOs involve the use of cross-species genetic exchange; recombinant DNA technology also can be used to transfer a gene between different varieties of the same species or to modify the expression of one or more of a given plant’s own genes, e.g., to amplify the expression of a gene for disease resistance.

More next issue.

If you desire more information on biotechnology, please contact our office at 805.934.6240.

Some information adapted from CAST, Issue Paper 12, December 1999.

NUTRIENT DEFICIENCY AND TOXICITY SYMPTOMS

In the April issue of Agricultural Highlights, I presented a general discussion on plant nutrition. Nutrient mobility in plants, soil analysis, and plant tissue analysis.

The following table provides some brief guidelines on plant symptom expression related to plant nutrient deficiencies or toxicities. It should be stressed, however, that once plants actually show deficiency or toxicity symptoms, the condition may not be correctable in the standing crop.

This is especially true in vegetable crops. Central Coast soils are known to have nutrient imbalances associated with magnesium, boron, iron, and calcium. Excesses or deficiencies of these elements can affect a plant’s ability to utilize the other essential nutrients. Periodic analysis of soil and plant tissues is the only way to make sure plant growth is normal and healthy.

Visual Deficiency and Toxicity Symptoms of Some Nutrients

Nutrient Type Visual Symptoms
Nitrogen Deficiency

Toxicity

Light green to yellow leaf color, older leaves, stunned growth.

Dark green foliar color, excess vegetation, vascular browning in roots and stems.
Phosphorus Deficiency

Toxicity

Leaves develop purple color, stunned growth, delay in plant development.

Excess phosporus may induce zinc and iron deficiency.
Potassium Deficiency

Toxicity

Older leaves turn yellow initially around margins.

Excess potassium induces magnesium and calcium deficiency.
Calcium Deficiency

Reduced growth or death of growing tips, poor fruit development, blossom-end rot, tissue collapse in fruit.

Excess calcium may cause magnesium and potassium deficiency.
Magnesium Deficiency

Toxicity

Initial yellowing of older leaves between leaf veins spreading to younger leaves, poor fruit development.

Imbalance with calcium and potassium may reduce growth.
Sulfur Deficiency

Initial yellowing of young leaves spreading to whole plant, similar symptoms to nitrogen deficiency, but occur on new growth.

Excess of sulfur may cause premature dropping of leaves.
Iron Deficiency

Toxicity

Interveinal yellowing in young leaves with fine veins still green. Young leaves completely yellow or white with some necrotic spots.

Possible bronzing of leaves.
Manganese Deficiency

Toxicity

Interveinal yellowing or mottling of young leaves.

Older leaves have brown spots surrounded by a chlorotic circle or zone.
Zinc Deficiency

Interveinal yellowing on young leaves, reduced leaf size ("little leaf").

Excess zinc may cause iron deficiency.
Boron Deficiency

Toxicity

Death of growing point and deformation of leaves with area of discoloration.

Leaf tips become yellow followed by necrosis. Leaves show scorched tips and margins.
Adapted from W.F. Bennet (Editor), 1993, Nutrient Deficiency and Toxicity in Crop Plant, APS Press, St. Paul, Minnesota, and H. Marschner, 1986, Mineral Nutrition in High Plant, Academic Press. Mortavalli, P., T. Marler, F. Cruz, and J. McConnelle, Fertilizer Facts! Essential Plant Nutrients, University of Guam.

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