Anyone feeding alfalfa or grass hay to their livestock in New Mexico this year is aware that it has become costly — and that's only if you can get it. Drought conditions and low allotments of water for irrigation have resulted in a reduced supply as demand has increased.

The development of alfalfa varieties that are more drought tolerant would obviously be a boon to both consumers and hay producers. Although alfalfa breeders at New Mexico State University have been developing better varieties of alfalfa since 1918, researchers are now combining high-tech genetic analysis with traditional plant breeding practices in this effort.

Ian Ray, a professor in the Department of Plant and Environmental Sciences, currently heads up NMSU's Alfalfa Breeding and Genetics Program. The approach he and Ph.D. candidate Gina Babb are taking in their search for more drought-resistant varieties is called "DNA marker-assisted selection."

"One of the research projects that we've been working on for actually over 10 years now is evaluating the potential to use DNA markers to improve alfalfa drought tolerance, specifically with reference to New Mexico, but hopefully also in a more general context, in areas of the Southern Great Plains and the Southwestern U.S. that are facing water shortages," Ray said.

The first phase of the project was a collaboration a decade ago between NMSU and the Samuel Roberts Noble Foundation, a nonprofit agricultural research center in Ardmore, Okla. Through that partnership, researchers were able to identify DNA "marker alleles" that were common to alfalfa populations that produced more forage and root biomass under low-water conditions. Partial funding for that project came from USDA grants and the Noble Foundation.

The current phase of the project, funded by grants from the Southwest Consortium on Plant Genetics and Water Resources and a Graduate Research Enhancement Grant from NMSU's vice president for research, uses DNA MAS to improve alfalfa forage production in drought-prone environments.

"The project that we have going on here involves transferring the DNA marker alleles, which we previously determined were associated with alfalfa productivity under water deficit conditions, into different types of alfalfa that farmers grow here in the state," Ray said, standing in the test plot late in the growing season. "Then we evaluate the effects of those DNA markers on forage productivity."

DNA markers

Ray indicated that they are not using genetic engineering approaches, where genes are isolated in a lab and then inserted into alfalfa. Rather, they use DNA markers to help them track and select for natural genetic differences for improved drought tolerance that are already present in alfalfa. Then, using traditional cross-breeding techniques, they transfer the DNA markers into alfalfa varieties, some of which are known to be sensitive to drought stress. The productivity of the offspring that carry the markers is then compared with their original varieties under deficit irrigation management to see if improvement in drought tolerance has occurred. 

The field research is taking place at NMSU's Leyendecker Plant Science Research Center south of Las Cruces, where 32 populations of alfalfa derived through the MAS technique were planted in 800 small plots. In this study, about 260 plots are being watered on a standard 14-day interval while the other 540 plots receive water every 28 days to simulate drought stress.

Productivity comparison was accomplished by harvesting all plots on a monthly basis during April, May, June, July, August and October 2011. To accomplish this, a special alfalfa forage-plot harvester, purchased with funds provided by USDA and the New Mexico Hay Association, weighed the biomass of each plot as it was cut. 

The forage weights for each plot were logged immediately, both electronically and manually, by Christopher Pierce, research technician for the program and operator of the harvester. Random hay samples were also collected during each harvest to determine forage moisture content, according to Pierce. This allows the harvest weights to be converted to dry tons per acre, the way farmers traditionally assess forage productivity.

Statistical analysis software programs are employed to analyze the yield date for significant differences in productivity among the different populations.

"It's been a very good year for us, in terms of collecting data," Pierce said. "Since we haven't had a lot of rainfall in 2011, we've actually been able to get six drought-stressed harvests off of our deficit irrigation study, which is pretty uncommon."

In late September, Ray was on site, inspecting the plots. "During 2011, we've documented that we're able to improve the performance of some populations by about 15 percent," Ray said, pointing to one particular field plot. "In general, we're seeing forage yield improvements of 7 to 10 percent — which can be attributed to specific DNA marker combinations that were previously shown to influence forage or root production."

In another part of the field, Ray identified a different MAS population that was developed from a drought-sensitive variety with a very leafy canopy composition. "What excites us about this particular research population is that not only have we improved its ability to out-yield the original variety under limited irrigation conditions, but its nutritive value should be high, as well, because of its leafy composition," Ray said. "So in an ideal world, our goal is to capture both high yield and high nutritive value in future varieties that we'll be releasing."

Ray also emphasized that the plants in this study will be evaluated for forage yield over three years to measure how the DNA markers influence alfalfa productivity over time. After the study is completed in 2013, the root biomass of all the populations will be assessed. This involves undercutting all the field plots with a tractor-pulled V-plow that Pierce built and weighing the root system of each population. Ray speculates that some of the increase in forage productivity may be related to more extensive root systems that enhance the plants' effectiveness in obtaining soil moisture.

"The great thing about this MAS approach is that it helps us track specific alfalfa chromosome segments that possess one or more genes which influence forage yield productivity during drought," Ray said. "In this way we can strategically develop new cultivars that will have improved forage yield capabilities under well-watered or drought-stress conditions."