Blog post by Dr Fred Muehlbauer, Professor (retired), USDA-ARS Grain Legume Genetics and Physiology Research Unit, Washington State University
Environmental degradation has been a developing problem in crop production and a challenge to plant breeders. With warmer and drier climates, abiotic stresses reduce yields and add to difficulties in breeding varieties adapted to increasingly stressful environments.
This challenge brings to mind a discussion I had as a beginning pulse crop breeder. The discussion centered on the statistical fact that yields of legumes, specifically pea and lentil, had not increased appreciably despite several decades of pulse crop breeding. I distinctly remember a statement made by a prominent farmer and I quote “After all this breeding, I don’t have any more lentils in my bin!” To that another farmer was quick to comment that he “hadn’t been farming the same farm he had 20 years ago.” Which was a very true statement as it is well documented that the region in question, his farm included, had suffered through decades of soil erosion on the steep and varying slopes typical of the fields of the region. Consequently, most of the valuable topsoil had washed down into nearby streams and rivers. It may well be said that breeding up to that time and since had been highly successful in maintaining earlier yield levels and that any increases made could be looked upon as a definite bonus.
The point is that while breeding may be making significant progress against yield limiting factors, such as heat and drought stress, and increased disease pressure, the changing environment represents a significant factor limiting success. While breeding can provide significant genetic improvement in legume varieties, collaboration with agronomists and particularly soil scientists is needed to enhance the agro-ecosystem in which they are grown.
Degraded soils takes one of several forms including wind erosion, water erosion, deterioration of physical properties and chemical degradation. Degradation in one or more of these forms increases biotic and abiotic stresses in legume crops and adversely affects symbiotic nitrogen fixation.
Breeders have devised various schemes (altered plant architecture, root systems, crop maturity etc.) designed to combat the effects of biotic and abiotic stresses and have looked to germplasm collections for the needed genes. Germplasm collections have been repeatedly evaluated for the genes needed to overcome the effects of all forms plant stress. Gene mining has attracted attention as a means of finding important genes and their locations in genomes. Introgression of those genes into new varieties, facilitated by closely linked genetic markers, holds promise for overcoming biotic and abiotic stresses. However, there is a limit to the variation available in collections of cultivated material and consequently increasing the emphasis on the wild species as the last resort for finding the needed genes.
Wild legume species are a mostly untapped source of needed genetic variation. Having survived for millennia under the most severe environmental conditions and faced with many of the same diseases and pests now plaguing current varieties, these germplasm sources are now recognized as critical sources of genes for stress tolerance. Bean breeders have found valuable genes in wild Phaseolus species while lentil breeders in Canada have used embryo rescue to facilitate crossing of otherwise incompatible wild Lens species with the cultigen. Recently, the crossable wild Cicer species have been systematically collected and efforts are underway to identify and introgress valuable genes to cultivated forms. Wild species exploitation is taking place in other pulse crops and hopefully will provide genes needed to make progress against biotic and abiotic stresses.
Legumes have an important role to play in restoration of soil health through symbiotic nitrogen fixation, residues for increasing soil organic matter, and providing needed “break” crops to aid in suppression of diseases affecting staple cereal crops. The role of legumes in food security and nutrition is well recognized. In view of the critical role legumes play in cropping systems, improvement of soil health and providing high protein food for an increasing world population, finding and deploying genes for stress tolerance in all its forms is recognized as a high priority research area. Progress in this area is critical to food security throughout the world.
Dr Fred is also a member of the Independent Advisory Committee of Grain Legumes.