The parasitic plant Striga, also known as witchweed, poses a threat to corn crops in Africa, which are vital for millions of Africans. UvA researchers led by professor Harro Bouwmeester discovered a strain of corn that is much less affected by Striga.
Striga is a beautiful plant with purple flowers, but appearances can be deceiving. Striga is parasitic and its growth comes at the expense of other plants.
Plants, such as corn, release signaling substances in the soil called strigolactones. “In the plant itself, they act like plant hormones. In the soil, strigolactones play a role in attracting beneficial microorganisms or fungi that help the plant. Witchweed takes advantage of this,” says professor of plant hormone biology Harro Bouwmeester.
In response to certain strigolactones, witchweed seeds that lie dormant in the soil germinate. “Witchweed invades the root of the host plant,” Bouwmeester continues. “So it can sap water and nutrients.” Not a nice neighbor, in other words.
Dormant for 20 years
Witchweed is very difficult to control, partly because the seeds can lie dormant for a long time: up to 20 years. In addition, it spreads easily. Bouwmeester says: “The seeds are tiny, almost like dust. They spread very easily, such as through wind, water or on tools.”
Striga is a pest in Africa, where about 60 percent of farmland is infested with the weed. “This often leads to the failure of entire crops, not only of corn but also of sorghum, millet, and rice. Some 10 million tons of grain are lost every year.”
The loss of so much grain due to witchweed poses a major problem for the food supply of about 300 million Africans. Bouwmeester's research group is also conducting research on other crops affected by Striga. “Our group investigates underground the communication and signaling of various plant species not just with witchweed, but also with micro-organisms. We think that this corn happens to be resistant to witchweed but was not bred for it.”
In a new study published in the journal Science, Changsheng Li, a PhD student with Bouwmeester, found a corn variety that is less affected by Striga. Bouwmeester: “Li discovered that the North American corn strain, which excretes different strigolactones than most other corn strains, including African ones, reduces witchweed germination.”
Striga does not occur in North America, although climate-wise it could. The United States has had a strict policy against witchweed since its accidental introduction in the 1950s. Entire A county in the U.S. is a geographic unit that is one level below the state. were sometimes quarantined to keep the weed in check. “We think this corn happened to be resistant to witchweed and was not bred for it,” says Bouwmeester.
The researchers have been able to identify which genes and enzymes in corn are responsible for producing the strigolactones that cause Striga to germinate. “We have observed that one of those genes is less active in the North American strain than in the African one. In a follow-up study, we will investigate whether we can also make that gene less active in African corn strains and what the consequences of that would be.”
Inactivating that gene will use biotechnology, says Bouwmeester. “We will use Crispr-Cas9.” Crispr-Cas is a kind of molecular scissors that can be used to make very precise, small adjustments to DNA. “We will then use those modified corn strains in Kenya to investigate whether the corn is also resistant to Striga in the field and whether the changes we make also have side effects, such as on the attraction of beneficial micro-organisms.”