By Chiseche Mwanza, Akshara Bathini, Trevor Palone, Greg Lutgen, Hannah Turner, Peggy Lamb and Jamie Sherman
Whether it is advantageous to die sooner or later is an important question for cereal crops, including barley. Timing of plant development is under both genetic and environmental control. For example, the timing of reproduction, called heading in barley, is impacted by barley genes, but can also be delayed by cooler weather or occur earlier in hot, dry weather. The same is true for the timing of plant maturity and mortality, a process called senescence. Genes program when death occurs in barley, but heat and drought can hasten, while cool temperatures and moisture can delay. In much the same way mother nature selects for the timing that works best for reproduction, plant breeders can also select for traits depending on environmental conditions and needs of growers and end users.
The timing of heading and maturity are of critical importance to barley yield and malt quality. The time from heading to maturity is often referred to as grain filling, during which starch and protein are transferred from the leaves into the seed, establishing both yield and malt quality. Extending grain fill can have both negative and positive effects depending on the environment.
When not to stay green?
Rich Horsley, the barley breeder at North Dakota State University, kindly provided stay green germplasm to both the Montana State University’s breeding program and to Australian researchers. Farmers in North Dakota found that staying green meant barley matured too late, delaying harvest, and increasing the chances of preharvest sprouting. So, in parts of the U.S. with plenty of rain during grain fill, staying green was a disadvantage.
When to stay green?
A common weather pattern in Montana is terminal drought. Spring barley in Montana generally heads in late June and early July, with grain fill extending into August. The barley producing regions throughout Montana often have little to no precipitation with high heat during this time, necessitating irrigation to ensure high malt quality with low protein and plump kernels. However, irrigation increases grower costs and the likelihood of disease, requiring pesticide application. Varieties requiring irrigation to make malt are risky for dry land farms, which encompasses about 80% of Montana’s farmland.
The Montana State breeding program has incorporated Horsley’s stay green types into breeding lines since 2015 and tested them under dry land and irrigation through a diverse range of weather conditions. To demonstrate the utility of extended grain fill to dry land production, we have instituted several studies: 1) Compared more than 200 stay green and non-stay green breeding material in two locations (one that is generally hot and dry and the other generally cooler and wetter across three seasons with varying levels of precipitation and temperature). 2) Evaluated non-stay green vs stay green lines at four different nitrogen rates over five years. 3) Genetically dissected the stay green trait and identified six important gene regions. 4) Developed sister lines varying genetically only at each of the six gene regions for study in a variety of treatments and environments to better understand the best deployment of the stay green trait. Important findings of all these studies are summarized below.
Advantages of extended grain fill:
- Stay green lines had higher yield in many dry land environments
- Stay green lines had better malt quality (higher percent plump grain, lower percent grain protein, higher malt extract, and better modification with lower β glucan and higher S/T).
- Stay green lines have higher percent plumps and lower percent protein under varying nitrogen rates.
- Stay green lines exposed to heat and drought during grain fill have more productive tillers and lower grain protein.
- Stay green lines tend to have a greater percent of deep roots and those roots are slower to senesce during grain fill.
The goal of our breeding program is to ensure growers can produce malt quality barley in Montana, where about 80% of available farmland is without irrigation. To ensure malt quality, protein levels must be moderated. A management decision made every year is the amount of nitrogen fertilizer to apply based on the anticipated yield potential. Therefore, nitrogen rates are determined at the beginning of the cropping season before the environmental conditions that impact yield potential are understood. When the environment does not support the predicted yield potential, nitrogen rates that are too high can cause grain protein to be too high and the percent plump grain to be too low for acceptable malt quality. If soil Nitrogen is too low, then the full formation of grain is not supported. Importantly, one of the stay green gene regions appears to scavenge nitrogen when fertility is low, potentially lowering nitrogen fertilizer use, an opportunity currently being researched.
Mini-rhizotron deep scans from a field trial in Havre, MT showing (left) stay green and (right) non-stay green roots. (Trevor Palone, 2024)
Benefits to the malt barley industry when staying green:
- Growers can produce high quality malt barley on dry land under variable management decisions and weather conditions.
- Malt barley can be produced more sustainably at lower cost, decreasing irrigation and potentially some pesticides.
- High quality malts are available to end users under variable weather conditions.