Project Details:

Title:
Determining the impact of multiple pests on soybean yields and grain composition

Parent Project: This is the first year of this project.
Checkoff Organization:Iowa Soybean Association
Categories:Breeding & genetics
Organization Project Code:
Project Year:2009
Lead Principal Investigator:Gustavo MacIntosh (Iowa State University)
Co-Principal Investigators:
Felicitas Avendano (Iowa State University)
Matthew O'Neal (Iowa State University)
Palle Pedersen (Iowa State University)
Gregory Tylka (Iowa State University)
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Project Summary

Soybeans with altered lipid composition are an attractive opportunity for growers to improve upon the profitability of soybean production. Without an understanding of how these common soybean pests act alone and in concert on these varieties, growers may be at risk of losing the premiums associated with these specialty bean varieties. Upon completion we will validate pest management recommendations based on commodity soybeans for production of low-linolenic soybeans or determining where modifications are needed for successful production.

The goal of this study is to better understand the relationship between soybean composition and agronomic stresses. Specifically we want to determine:

1. The impact of soybean aphids, soybean cyst nematode, and brown stem rot, alone and in combination, on yield and composition of commodity and low linolenic varieties.

2. The susceptibility of low-linolenic soybean varieties to soybean aphids, soybean cyst nematode and brown stem rot; and

3. Whether soybean leaf fatty acid levels can be used to predict differences in soybean grain composition.

A field microplot experiment (6 replicates) was conducted during the 2008 season. The experiment included two 1% linolenate cultivars (one has PI88788-derived source of resistance to SCN), one 3% linolenate cultivar resistant to SCN, and two 7% linolenate cultivars (one with PI88788-derived source of resistance to SCN). All varieties are susceptible to SBA and BSR. Plants of each variety were challenged with one of three pests alone or in combination. There was also a no pest treatment (as a control) and two treatments for SBA - an uncontrolled level and one in which aphid populations were allowed to reach threshold levels (250 aphids/plant) and then treated with insecticide.

Initial analysis of aphid populations in the different lines showed that the low-linolenic/SCN-susceptible variety was more susceptible to aphid infestation. However, there seems to be an effect of the SCN resistance gene on aphid numbers, since aphids on the low-linolenic/SCN resistant line were lower. A similar effect of the SCN resistant gene could be observed in the 7% varieties. The presence of other pests seemed to have a negative effect on aphid numbers. SCN and BSR analyses are still underway, due to the delay in harvest as a consequence of flooding and late planting. However, greenhouse bioassays showed that low linolenic varieties are as susceptible to SCN as other susceptible varieties. Results from a pilot microplot experiment and green house experiments suggest that low-linolenic varieties are also more susceptible to caterpillar damage.

Yield analysis is underway to determine the impact of SBA, SCN, and BSR, alone or in combination, on yield of commodity and low-linolenic varieties. Aphid treatments (alone or in combination with other pests) caused a decrease in plant height for all the varieties tested. The effect of SBA, SCN, and BSR, alone or in combination, on grain composition in commodity and low linolenic varieties will be measured once yield analyses are completed.

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