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United States Department of Agriculture

Agricultural Research Service

Chemistry
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1 - Beneficial Uses of Peanut By-products
2 - Low Cost Aflatoxin Analysis
3 - Natural Peanut Resistence to Pests
Natural Peanut Resistence to Pests


Do we know everything that we should know about peanut physiology?

No, particularly not enough is known about peanut natural defensive mechanisms against pests.

Phytoalexins. Peanuts can naturally fight diseases by producing antibiotic compounds (stilbene phytoalexins). However, the exact mechanism of peanut resistance to fungal invasion is not understood. A greater understanding of peanut resistance to pests can lead to new beneficial agricultural practices. Manipulation of host plant resistance is an efficient, economical and environment-friendly approach used to manage many pests and diseases of agricultural crops. In addition, stilbene phytoalexins may be considered potential chemical markers in breeding programs for disease-resistant peanuts.

Peanut kernel infected by fungus showing phytoalexin production

A dissected peanut kernel infected by a soil fungus (Aspergillus niger). Yellow-colored  phytoalexin is locally produced by the kernel tissues (arrow). The phytoalexin (termed SB-1, the structure is shown) was first discovered at the NPRL.

 Photomicrograph of peanut root tip
Photomicrograph of peanut root tip showing the yellow mucilage layer. Seven new hydrophobic prenylated stilbenoids, including mucilagin A, were isolated from the mucilage for the first time; their structures were elucidated. These compounds were restricted to mucilage, which suggests their special role in regulating root-soil pathogen interactions.

Interrelationship of stilbene phytoalexin production and resistance of several peanut genotypes to major peanut diseases, including TSWV was also demonstrated for the first time.

 Interrelationship of phytoalexin production and peanut resistance to major diseases

Ability of peanut genotype to synthesize stilbene phytoalexins

Table showing interrelationship of phytoalexin production and peanut resistance to major diseases.

Susceptability of peanut genotypes to major diseases including: TSWV*, WM*, and LLS*.

 * TSWV, tomato spotted wilt virus; WM, White Mold; LLS, Late Leafspot

 

Flavonoids and spermidines. Sound seed yield depends heavily on high peanut resistance to pests and uncompromised plant fertility. Peanut flowers have been considered resistant to pests. Compounds that may be responsible for such resistance have not been investigated.


The study revealed the production of flavonoid and spermidine conjugates in the peanut flower at high levels. All major metabolites have been detected in the flowers for the first time. One of the metabolites, acetyldicoumaroylspermidine (structure is shown below), has not been previously reported in plants. Both flavonoid and spermidine conjugates may play a protective role against pests as it has been shown for similar compounds in other plants. The new spermidine conjugate may be involved in regulating the plant reproduction process.

Peanut flower

Chemical structure of a new spermidine derivative.

Shown are the  peanut flower and the structure of a new spermidine derivative. 1 – standard; 2 – one of two symmetrical wings (one of the wings is removed for a better observation of the keel); 3 – keel (2 fused petals that enclose pistil and stamens); 4 – hypanthium.

Spermidine compounds, similar to the one above, have been reported to appreciably inhibit HIV-1 protease that is essential for the life-cycle of HIV. One of the compounds also demonstrated high activity against Helicobacter pylori, a major etiological agent in gastroduodenal disorders. Study of biological activity of the new peanut spermidine derivative is anticipated.

 

For more information contact Victor Sobolev.

 

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Last Modified: 1/22/2009
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