Wheat and more wheat, multiple varieties in one field

LEFT: A wheat field in one year of the researchers’ experiments. Here, different varieties are noticeable because of physical differences – namely colour or hue and if the head has awns on it or not. RIGHT: Shown here is the difference of a fungicide application within one variety. The left side of the photo shows the control side of the plot that had no chemical fungicide applied. The slightly darker colouring of the wheat is largely due to disease. The right side of the photo shows the fungicide-sprayed side of the plot. The lighter colouring is healthier wheat, which often also has a few additional days to mature, thereby increasing yield. | Julie Baniszewski photos

Researchers have found that several wheat varieties mixed in the same crop offer disease and insect protection

Growing multiple varieties of wheat together can reduce disease pressure as much as a fungicide application does, according to research out of Pennsylvania State University.

Julie Baniszewski led the research project that compared a wheat crop composed of four different varieties, to a single wheat variety that received a fungicide application, as well as a check that did not get any fungicide.

The three-year field experiment was designed to see if the mixtures could suppress diseases, increase predation of insect pests and increase yield and economic value.

Insect predation was quantified by using aphid populations, and disease, yield, and economic return over variable costs for each plot were assessed.

“The mixed variety plots had inhibited the spread of foliar disease in the field comparable to the fungicide application,” Baniszewski said.

She said the plot with four wheat varieties inhibited foliar disease by 20-25 percent.

However, she cautioned the intra-specific treatment was not the highest yielding, nor did it provide the greatest return over variable costs.

There was low aphid presence throughout the study and no difference was observed between the treatments.

Intra-specific crops contain multiple varieties of the same crop, while inter-specific crops have different species in the same crop.

In Saskatchewan, a few growers use inter-specific crops, or multi-crops, to reduce disease pressure, including a paired row lentils and flax system.

In this practice, the two rows of flax physically stops disease such as ascochyta from spreading through the lentils.

Various head diseases are shown among the different varieties of wheat in the study. | Julie Baniszewski photo

Baniszewski said instead of a physical barrier as with the flax lentil paired row multi-crop, the inter-specific wheat crop has a dilution effect in terms of susceptibility to pathogens.

“If you apply different varieties and only one was susceptible to spread the disease and the other varieties that are resistant to that disease, it’s not as likely to spread,” Baniszewski said.

She said by deploying a wide variety of resistance in the germplasm of the multiple varieties, it’s more likely that some of the varieties will be resistant to any particular disease.

“Each variety would have a different set of traits. One may be high yielding, another resistant to insect pests and yet another resistant to specific diseases,” Baniszewski said.

“By combining these different sets of traits, the crop is more consistent year to year. The field is more diverse genetically and better able to reduce or withstand pest abundances and diseases.”

Selecting the right wheat varieties is key to making this system work. Not only do growers want to choose varieties with diverse disease resistance packages, they also want to choose varieties that will mature at the same time, and have similar height.

Aphids, a common pest in wheat, were lightly glued onto cardstock and monitored for 24 hours to quantify predation by native insects. The card on the right shows that four tiny aphids remain; the card the left shows the aphids were consumed by a ladybird beetle. | Julie Baniszewski photo

Baniszewski said it’s likely that on most years an intra-specific crop will not yield as well as a mono crop with a higher yield potential then the average potential of the varieties in the mixed crop.

However, she said the practice can serve as a risk management move, or an insurance policy. If there is a pest or disease infestation or if there is a drought or excessive rain, seeding a diverse set of wheat varieties at the same time could be beneficial.

“I’m actually in the entomology department, and one of the main ideas behind this was to see if by having these different varieties we could attract more beneficial insects. The problem was that we didn’t have any pests at all while we were doing the study,” Baniszewski said.

“But if there was some kind of pest outbreak, the same idea that there’s different varieties, there’s different genetics and there might be some kind of attractant that one variety has to bring in, you know lace-wings or lady bird beetles or something that’s a predator of some of these pests.”

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