HOST RESISTANCE

Question 1

Host Resistance:

A preventative pest management tool that takes advantage of the genetic attributes of certain plant cultivars allowing for resistance or toleration from pest attack.

Answer 1

• One of the most effective and least expensive pest management tools.
• Common for pathogen’s and nematodes.
• To a more limited extent arthropods.
• Not always a full proof method; susceptibility due in part too the physical stressors of the env. (temp., plant and soil nutrition, evaporation rate, moisture).
• Resistant biotypes can arise.
• A cultivar that is resistant to one pest may be highly susceptible to another.
• Integration of resistant cultivars with other management tools such as sanitation, crop rotation, and certified seed can prolong the resistance.

Question 2

1. ) Tolerance
2. ) Resistance (True Resistance)
3. ) Apparent resistance (disease escape)

Answer 2

1. ) Able to endure the presence of a pest with little or no long-term damage.
2. ) Support few or no pest individuals and have physiological or morphological characters that affect the behavior (antixenosis) or biology (antibiosis) of the pest management.
3. ) Involves plants that fail to become infected with a pathogen because all the requirements for infection or disease development (e.g. environmental conditions, susceptible host stage, or pathogen inoculum) were not present. In other word under different conditions the plant would be susceptible to the disease.

Question 3

Antixenosis
(non-preference)

Antibiosis
-Allelopathy

Answer 3

Change in plant color, odor, hairs, or leaf texture that make the plant unattractive or a repellent.

The secretion of a compound by one organism that inhibit vital activities of another (for IPM purposes directed toward the pest).

-A form of antibiosis whereby the secretion of toxicity is from one plant species toward another. (Either through volatile gases, root/shoot oils,etc).

Question 4

Horizontal (polygenic) Resistance

Vertical Resistance

Answer 4

Results from the activity of one or a few closely linked genes. Tends to involve numerous minor processes and defenses working together that affect a broad range of pathogen. Thought to be slightly less effective though usually lasts longer.

Relies on more than one gene and preferably on more than one character for the mechanism of resistance. Usually impacts the major functions of specific pathogens and therefore very effective toward a particular strain, however more easily selected against.

Question 5

Techniques for Developing Plant Resistance

Answer 5

Simple Selection

Pure Line Selection

Backcrossing

Question 6

Simple Selection

Traditional Approach

Answer 6

Researchers monitor fields where natural infection occurs regularly and select seeds from the most highly resistant plants.

The selected seeds are replanted together so that cross pollination may transpire, and the process is repeated.

Generally a slow process.

Question 7

Pure Line Selection

Answer 7

Resistant parents (with less desirable agronomic qualities) are crossed with a parent that has desirable traits (though lacks resistance). Certain individual offspring from this cross that have resistance and good agronomic characteristics, and are propagated under controlled conditions. This continues for several generation, repeatedly inoculating for resistance, and evaluating for ag. traits, until the lot becomes a true breeding cultivar.

Offspring of individual parents are kept separate throughout the process to obtain genetic purity.

These cultivars are homozygous for the resistant genes and usually have a high degree of specific vertical resistance but a low degree of horizontal.

Question 8

Backcrossing

Answer 8

Cultivars are developed similarly to the method described for pure line selection, EXCEPT, several crosses are made back to the parent that has desirable agronomic traits in subsequent generations throughout the varietal development programs.
As a result, there is variation (heterozygosity) within the cultivar for diseases resistance, thus reducing the pathogens ability to overcome resistance.

Question 9

Trans-genic Pest Resistance

Answer 9

Results from the transfer of desirable traits, from one organism to another.
Through bio engineering, gene insertion from one organism to another can encrypt new building blocks toward resistance within the plant cultivars D.N.A structure.

Question 10

Nonhost-Alternatehost Plants.

Answer 10

When a pest infestation becomes overwhelming, resistance breaks down, or control options are simply to expensive; the use of alternate host plants with no predisposition toward pestilence, can be a viable option.