Research The Bayer Scientific Magazin, Edition 28

search for additional solutions to combat the devastating disease, 

joining forces with big players in the juice industry. The crop pro-

tection experts are aiming to make orange trees more resistant 

to the disease with the tried-and-proven Bayer active substance 

fosetyl-aluminum. This is the active component of the fungicide 

Aliette™, which is used to treat apples, pears and grapevines. “We 

use it, for instance, to immunize the young plants and strengthen 

their defense systems,” says Dr. Christoph Andreas Braun of Prod-

uct & Project Support Disease Control, Bayer CropScience. In the 

coming years, researchers want to use the active substance to help 

citrus plants as well. Bayer is not limiting its efforts to just profes-

sional citrus growers. In California, specialists from Bayer are also 

teaching residential fruit growers how to manange the insect pest 

to help keep Californian citrus trees free from the disease. Together 

with California Citrus Mutual, Bayer has founded an initiative called 

Citrus Matters to promote education of backyard citrus growers. 

“Commercial citrus growers in California are able to manage the 

psyllids and monitor their groves regularly. But the threat to their 

plantations remains in place if citrus greening infests the countless 

citrus trees in people’s yards,” says Wirtz. The goal of the campaign 

is to make homeowners who have citrus trees on their property 

aware of the dangers posed by the disease and to enable them to 

help stop the spread of the Asian citrus psyllid in California. 

In order to effectively combat citrus greening, citrus growers 

must prevent their trees from becoming infected with the bac-

teria in the first place. That is easier said than done. “You have 

to kill the psyllids before they feed on the sap and are able to 

transmit yellow dragon disease,” Wirtz explains. Bayer research-

ers therefore have to become better acquainted with the pest. 

The first step: careful monitoring of the psyllids and the patho-

gen. Bayer and its external Food Chain Partners therefore plan to 

join forces to create “model farms” in Florida and other growing 

regions in Latin America. “A holistic approach will be crucial for 

effectively controlling citrus greening in the future,” Wirtz says. 

But Bayer’s specialists have also set their sights on another long-

term goal: highly specialized antibacterial solutions to combat 

citrus greening. Initial tests are already under way.

Bayer specialists are also supporting research to use the 

psyllids’ natural enemy, Tamarixia radiata, to combat them. This 

wasp lays its eggs on the psyllid nymphs. When the wasps hatch, 

they feed on the young psyllids, thus reducing the population 

of the disease vector. In Brazil, Bayer CropScience is supporting 

placement of breeding stations for this species of wasp in private 

orange groves, and the first field tests of this form of biological 

pest control are now being conducted in commercial plantations. 

As yet another approach, Bayer has teamed up with researchers 

in California and São Paolo to develop pheromone traps, which 

use female sexual pheromones to attract the male psyllids. “In the 

future, we may be able to develop selective traps and substantial-

ly reduce the population of psyllids,” explains Dr. Peter Lösel, an 

insect physiologist in Pest Control Biology at Bayer CropScience. 

Around the globe, Bayer scientists and their research col-

leagues are working together to develop integrated measures to 

combat citrus greening and tame the yellow dragon. 

Research in the lab leads to solutions in the field: Dr. Christoph Andreas Braun and Kai Wirtz (photo left, left to right) are working at top speed to 

develop efficient strategies and active ingredients to combat citrus greening and its vector, the Asian citrus psyllid (photo center). The bacterium trans-

mitted by this plant parasite causes terrible damage to citrus plants – for example, leading them to produce only small, immature fruit (photo right).

Unrecognized threat

Citrus greening was first recorded in India in the 18th century. 

This is likely also where the chain of infected plants began. The 

disease was recognized in China in the 19th century and named 

Huanglongbing (yellow dragon). Citrus greening is now wide-

spread in Asia, South Africa, Brazil and North America. Citrus 

plants in Cuba are also afflicted, and in 2015, psyllids were 

found in Spain and Portugal for the first time, and may be the 

harbingers of citrus greening in Europe.

www.research.bayer.com/

citrus-greening

More information on this subject

Scientists working with partners worldwide to 

develop solutions to citrus greening

Bayer research 28    July 2015

47

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CROP PROTECTION FOR TEXTILE PRODUCTION

Bacillus  

thuringiensis

Cry2Ae

Cry1Ab

GlyTol™/LibertyLink™

1

 

The TwinLink™ system employs two genes 

taken from the soil bacterium 

Bacillus thuring-

iensis (Bt).

 These genes produce the proteins  

Cry1Ab

 and 

Cry2Ae 

that combat ravenous  

Lepidopteran larvae.  The Bt gene is integrated 

into the genome of the cotton plant, making  

it capable of protecting itself against  

pests like the cotton bollworm.

3

 

Above-ground protection 

from caterpillar pests – farmers 

require fewer pesticides for their 

fields. The cotton plants also 

produce greater quantities of 

longer and therefore better- 

quality fibers.

Result

2

 

The TwinLink™ technology is available to farmers 

commercially with 

GlyTol™

 and 

LibertyLink™

 technol-

ogies – genes which make cotton plants additionally 

resistant to the herbicides glyphosate and  Liberty™.

“The TwinLink system 

protects cotton plants 

against caterpillar pests 

and provides full toler-

ance to glyphosate and 

Liberty herbicides, helping 

them achieve excellent 

harvests and peak fiber 

quality. That means better 

profitability for cotton 

farmers.”

Paul Callaghan, 

 Director, Global Cotton 

Seeds Marketing

All-round protection for quality fibers

The natural fiber cotton is an extremely valuable resource for the textile industry, and is also used in the production of paper and 

packaging materials. However, pests such as the cotton bollworm can severely reduce harvest yields and compromise the quality 

of the fibers. The TwinLink™ technology protects cotton plants against hungry caterpillars.

Photo: private (1)

AGRICULTURE 

TwinLink

48

Bayer research 28    July 2015

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