The Van Trump Report

New Grafting Technique Could Help Combat Pathogens in the World’s Most Imperiled Crops

Researchers for the first time have made grafting work in “monocotyledons”, a type of plant that includes are some of the world’s most important plants economically and culturally, and account for most of our staple foods. The “near-impossible” technique could increase production and eliminate diseases for some of agriculture’s most imperiled crops.

An estimated 60,000 plants fall under the classification of monocotyledons, aka “monocots,” which are grass and grass-like flowering plants, the seeds of which typically contain only one embryonic leaf, or cotyledon. In agriculture, the majority of the biomass produced comes from monocotyledons. These include not only major grains (rice, wheat, corn, etc.), but also forage grasses, sugar cane, and the bamboos. Other economically important monocotyledon crops include various palms (Arecaceae), pineapple, and as mentioned, bananas.

Grafting is the technique of joining the shoot of one plant with the root of another, so they continue to grow together as one. Grafting has been used widely since antiquity in another plant group called the dicotyledons that include orchard crops like apples and cherries, and high value annual crops like tomatoes and cucumbers. The process is commonly used to impart beneficial properties, such as disease resistance or earlier flowering. Until now it was thought impossible to graft grass-like plants in the monocot group because they lack a specific tissue type, called the vascular cambium, in their stem.

Researchers at the University of Cambridge have discovered that root and shoot tissues taken from the seeds of monocotyledonous grasses—representing their earliest embryonic stages—fuse efficiently. Their results were published recently in the journal Nature. “We’ve achieved something that everyone said was impossible. Grafting embryonic tissue holds real potential across a range of grass-like species. We found that even distantly related species, separated by deep evolutionary time, are graft compatible,” said Professor Julian Hibberd in the University of Cambridge’s Department of Plant Sciences, senior author of the report.

The technique allows monocotyledons of the same species, and of two different species, to be grafted effectively. Grafting genetically different root and shoot tissues can result in a plant with new traits—ranging from dwarf shoots, to pest and disease resistance. The technique was effective in a range of crop plants including pineapple, banana, onion, tequila agave, and date palm. This was confirmed through various tests, including the injection of fluorescent dye into the plant roots—from where it was seen to move up the plant and across the graft junction.

Dr. Greg Reeves, a Gates Cambridge Scholar in the University of Cambridge Department of Plant Sciences, and first author of the paper, says that making important food crops resistant to the diseases that are destroying them is an “urgent challenge.” One such crop is the Cavendish banana, which accounts for around 99% of the bananas sold globally. The variety is a clone designed to withstand long-distance transportation but with no genetic diversity between plants, the crop is highly vulnerable to diseases like Panama disease, which is caused by a soil-borne fungus. And Cavendish bananas are sterile, so disease resistance can’t be bred into future generations of the plant. By grafting more disease-resistant stems (or rootstocks) with the banana plant, the Cavendish could be bred to avoid Panama disease.

The team’s preliminary studies in the lab also suggest that the grafting can work between species. They grafted a wheat shoot to disease-resistant oat roots. This may protect the wheat from soil-borne disease, although it is still unclear whether the procedure is really feasible for wheat and other grasses as the process might need to be repeated millions of times for a single harvest. But for large plants that live for many years and generate high-value produce, like date palm or tequila agave, the method could prove to be cost-effective.

The researchers have filed a patent for their grafting technique through Cambridge Enterprise. They have also received funding from Ceres Agri-Tech, a knowledge exchange partnership between five leading UK universities and three renowned agricultural research institutes. (Sources: Nature, New Scientist)

Monocots and dicots vector illustration. Labeled plant comparison division scheme. Educational graphic with seed, root, vascular, leaf and flower differences from botany aspect. School biology handout

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