Do Commercially Available Inoculants Work on New Saline Tolerant Alfalfa Varieties?

Background

It becomes an increasingly important topic to produce stable forage feed, because forage acres are decreasing in Canada. One of strategies would be to expand alfalfa production in low productive land including saline regions as many annual crops fail to produce economical yield in marginal land. Development of new salt resistance alfalfa cultivars is a necessary approach for this purpose. Researchers also need to test other options such as application of beneficial soil bacteria (inoculants) to improve alfalfa resistance to abiotic stresses.    

Objectives

• To investigate the effect of continuous selection of alfalfa for improved salt tolerance on root nodule formation, and alfalfa agronomic performance under salt stress.
• To quantify effect of a salt tolerant bacterium on alfalfa growth under salt stress as compared to a common inoculant.

What they will do

In this study, researchers tested to see if new breeding materials of salinity tolerant alfalfa respond better to salt tolerant inoculants than previously available alfalfa cultivars. In this greenhouse trial, they compared 3 newly developed salt tolerant breeding populations and Halo-II alfalfa at three different salinity levels. Within those, they tested non-inoculated alfalfa, inoculation with a common strain (Ensifer meliloti) for biological N fixation, inoculation with a salt tolerant bacteria (Halomonas maura or co-inoculation with the common strain as well as H. Maura.

What You Learned

The recurrent selection of alfalfa under high salt stress increased alfalfa salt resistance, with the alfalfa Generation 2 population paired with nitrogen amendments (~60kg/ha) being capable of mediating the effects of 8ds/m salinity stress for two months. Generation 2 population also produced the most biomass at 120 days in tandem with the common inoculant strain. However, continuous recurrent selections might have increased in-breeding depression in alfalfa Generation 3 population as demonstrated by reduction of yield compared to Generation 2. This suggests inclusion of different salt tolerant germplasm would be important for further recurrent selection. No treatment was capable of mediating the effects of 16ds/m salinity, and the majority of alfalfa plants were dead after four months of treatments at this level. Interestingly, alfalfa selection under high salt stress has increased plant height. We also observed Generation 3 population in combination with nitrogen amendments (~60kg/ha) exhibited elevated levels of shoot osmoprotectant (Glycine betaine) levels at 120 days. We did not observe clear improvement of alfalfa salt tolerant after inoculating with salt tolerant bacteria H. Maura. However, there was a positive effect of inoculating with biological N fixing E. meliloti at medium salt stress.

What it Means

Recurrent selection for salinity tolerance in alfalfa appears to favour increased performance in both saline and non- saline conditions, especially with nitrogen supplementation. This experiment indicated that nitrogen is a limiting factor in relation to alfalfa growth in saline conditions. As the salt tolerant breeding materials and the check cultivar did not survive under under high salt stress (16dS/m E.C), incoporation of new breeding approaches such as molecular marker assisted selection will be useful for increasing genetic gain in alfalfa salt tolerant breeding.