Lignin is a major component of plant cell walls that provides physical strength to plants, but, higher lignin concentrations can negatively affect forage digestibility. Therefore, it is best to reduce, but not eliminate, lignin in forage crops. Eliminating total lignin content can severely alter plant growth and performance in the field.
Noble researchers have identified certain alfalfa genes whose expression, when altered, reduces lignin content without compromising plant yield. This discovery led to the development of HarvXtra, the first genetically engineered alfalfa with a trait to improve forage quality. HarvXtra alfalfa lines can increase forage yield by 20 percent and can delay harvest to 35-day cutting intervals compared to 28-day cutting intervals for conventional alfalfa varieties. In addition to increased yield, HarvXtra alfalfa has 14 to 18 percent higher relative forage quality when compared to conventional alfalfa varieties.
The health of reduced lignin plants in the field is a concern since lignin also plays an important role in plant defense against pathogens. There is a general perception that lignin reduction would negatively affect plant health. Unexpectedly, we found that certain reduced lignin alfalfa lines were resistant to a few soil-borne fungal pathogens. Further investigation revealed that when certain genes involved in lignin production are downregulated, the energy is shifted to a different pathway that makes antifungal compounds called flavonoids that make the plants resistant to some fungal pathogens. Such a phenomenon has also been observed in sorghum. Therefore, targeted lignin modification can also be used in other legume and forage grasses to confer resistance against pathogens. This will provide double benefit to forage crops: increased forage quality and increased disease resistance.
There are several genes involved in producing lignin. Not all of these genes will result in enhanced plant defense responses when downregulated. Most genes can affect the plant performance in the field when downregulated. Therefore, care should be taken to alter the expression of an appropriate lignin production gene to give resistance. The gene can also vary depending on the plant species, so extensive research is needed before selecting and altering the expression of a lignin production gene. Nevertheless, altering lignin production in forage crops holds a great promise to increase profitability to farmers and ranchers by increasing forage quality and yield. With the recent invention of gene editing technologies, targeted alteration of lignin biosynthesis in forage crops can be done in a nontransgenic manner.
HarvXtra is sold by Forage Genetics International. More information can be found at: www.foragegenetics.com/Products-Technologies/HarvXtra-Alfalfa.