Insect resistance in soybean

Why is there a need for insect resistance in soybean?

• The photo at left reveals the type of damage an infestation of velvetbean caterpillar can do in a couple of days if not controlled.
• The photo at right shows the implementation of insect control measures.

Which are some of the major lepidopteran pests of soybean?

• Left: Velvetbean caterpillar, Anticarsia gemnatalis
• Middle: Corn earworm, Helicoverpa zea
• Right: Soybean looper, Pseudoplusia includens

Genetically engineered resistance in soybean

• Left: Bacillus thuringiensis, a ubiquitous soil bacterium that is the source of the gene for insect resistance
• Right, Back row: Bt-soybean, with a single gene from B. thuringiensis; Front row, regular soybean. Both were subjected to feeding by velvetbean caterpillar

But, note that Bt-soybean is not equally effective against all caterpillars:

• Left: Bt-soybean + Velvetbean caterpillar
• Right: Bt-soybean + Corn earworm

And, not all soybeans are equally susceptible to insect feeding. Compare after feeding by corn earworm:

• Left: Soybean with no insect resistance
• Middle: Bt soybean
• Right: Soybean with resistance derived from PI 229358, a semi-domesticated soybean introduced from Japan

The insect resistance of PI 229358 is conditioned primarily by a major Quantitative Trait Locus in a 1-cM segment located between markers Satt626 and Satt702 of Linkage Group M, called QTL-M

• Left: Closeup of LG M, where a major QTL for insect resistance is located
• Right: Fluorescently labelled microsatellite markers flanking QTL-M and other QTLs for insect resistance

Using marker-assisted selection to obtain soybean lines that differ only by the presence or absence of QTL-M, we can show a synergistic interaction between QTL-M and the trasngenic Bt, following feeding by corn earworm:

• Left: Soybean with no insect resistance
• Middle Left: Bt soybean
• Middle Right: QTL-M soybean
• Right: Bt + QTL-M soybean

What is next?

• Clone QTL-M
BAC library has been made from PI 229358
Markers ±0.5 cM of QTL-M will be used to find the corresponding BACs from Williams 82
These BACs will be used to find their counterparts from PI 229358
These BACS will be fingerprinted and assembled into a contig