One way to kill a dangerous pest could be to encourage it to grow

The best way to rid fields of a dangerous weed is to help it germinate. Boubacar Kountche and colleagues call the technique ‘suicidal germination’ in their paper in Plants, People, Planet. “Our results clearly demonstrate the effectiveness of the developed protocol… to suppress Striga emergence in highly infested fields up to 65%,” wrote the authors. They say that not only is their treatment effective, the low inputs needed also make it practical.

Striga hermonthica and Striga asiatica are plant parasites that are particularly difficult to remove. They live as root parasites. As seeds they lie in wait in the soil. What they are waiting for are plant hormones known as strigolactones. These hormones have several tasks including encouraging mycorrhizal fungi to grow towards plant roots. The Striga seed picks up the strigolactone signal, indicating there is a suitable host around and germinates. It them works out where the host is and works to the source. Here, a parasitic tendril, a haustorium, taps into the root and starts siphoning food back to the Striga plant. The Striga plant develops underground and out of sight. When it’s ready it grows rapidly up, flowers and seeds.

Striga is a particularly dangerous pest as it can destroy up to 100% of yield. It’s subterreanean lifestyle means it cannot be spotted until it has struck. Without a host, the seed can remain dormant in the soil for years. Striga has to be patient, as it cannot make its own food. When it starts growing the haustoria, it has to strike a plant root before its energy reserves are used up. This is weakness that Kountche’s team has exploited.

The team has produced artificial strigolactones. These can be applied to fallow soils. With no crops in the field the germinating Striga plants cannot damage the harvest. More importantly, without supporting plants, the Striga plants that do germinate have no support. So they germinate without hope of a victim, hence the ‘suicidal germination’. Tests using these strigolactones managed to cause germination in over 60% of the seed bank in some cases. The application requires no extra water, an important factor in many of the farms that could benefit from this treatment.

“The farming systems in which parasitic weeds represent a major problem are subject to a variety of crop production systems,” say the authors. “The impact of the diversity of farm management practices on the suicidal germination approach has not been evaluated yet. The next step in combating parasitic weeds would be to consider how to integrate the suicidal germination approach in different crop management systems.” They propose a combination of planting with non-host plants such as cowpea or sesame and fallow periods for the soil. In addition to being the most effective and least expensive method to improve soil fertility, a rotation of this scheme over several years is expected to drastically reduce or even eliminate the parasitic seedbank in infested fields of sub‐Saharan Africa.”