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Sudan and sorghum genetic traits offer improved forage potential

Bruce Anderson Published on 30 April 2014
Summer annual forage grasses often are an important part of many hay, silage and pasture plans. Sudans and sorghums can produce much forage even under dry growing conditions. However, these forages tend to be more stemmy and less digestible than many cattle and cattle producers prefer.

Cultural practices like harvest timing, grazing management, seeding rate, row spacing and fertilization can overcome some, but not all, of these limitations. Recent advances in genetic traits provide additional methods to improve the use of these forages. Consider the following traits when selecting sudans and sorghums to plant for forage.

BMR
BMR stands for “brown mid-rib.” It received this name because the mid-rib or vein that runs down the center of each leaf has a brownish tint in summer annual grasses instead of the normal whitish color.

The color of the mid-rib, though, is not what is important. The important characteristic is how the BMR gene affects lignin and forage quality. Lignin is a complex compound that attaches to fiber components like cellulose in the plant. This makes the plant more rigid and the fiber less digestible.

Grasses that have the BMR gene produce less lignin than normal plants. As a result, more of the fiber can be digested by cattle, increasing the energy value of the forage. Since reduced lignin tends to also make the stalk softer, animals often eat more of it, thus reducing waste.

Plants with the BMR gene tend to lodge more easily and yield less than non-BMR plants. Fortunately, plant breeders have overcome most of these negative consequences of the BMR trait. Nonetheless, use care when selecting varieties of BMR-containing sudans and sorghums to plant.

Brachytic dwarf
One of the more interesting and potentially valuable traits that plant breeders have been developing for sudans and sorghums is brachytic dwarf. Historically, sudans and sorghums used as forage have tended to be tall and stemmy, with a tendency to lodge easily.

The brachytic dwarf trait shortens and thickens the internodes between leaves. This produces shorter plants with improved standability, high leaf to stem ratios, and good tillering potential. Despite being shorter, tonnage is very similar to taller sorghums.

The brachytic dwarf trait should be of special value in forage sorghums intended for silage as they have the greatest tendency to lodge. The good tillering potential of many brachytic dwarf varieties also may be valuable in forage programs that harvest sudans and sorghums multiple times.

Male sterile
Male sterile plants do not produce pollen. If no other source of compatible pollen is around, male sterile plants produce no grain so all the sugars and proteins produced by the leaves remain in the leaves and stalk instead of translocating to the grain. This results in higher forage quality and palatability.

Male sterile plants are more susceptible to ergot, however. In addition, pollen from close relatives, like johnsongrass or shattercane or nearby fields of sudans and sorghums, can fertilize male sterile plants and cause them to produce grain.

Photoperiod sensitive
Heading and flowering of most summer annual grasses is controlled primarily by heat units rather than photoperiod. Plants that are photoperiod sensitive, however, do not initiate heading until day length is less than about 12.5 hours.

These plants remain vegetative for most of the growing season. Instead of forming seedheads, photoperiod sensitive plants continue to add new leaves. This allows them to maintain high forage quality and can provide extra flexibility in timing harvest, especially during unfavorable weather.

Forage quality declines very rapidly, though, late in the season once heading and flowering do initiate.

High sugar
Sweet sorghums have been around for decades. Recently, plant breeders have successfully incorporated more of the genetics of high stalk sugar into forage types to increase energy content and palatability.

Combinations
Most beneficial of all is the opportunity to include two or more of these genetic traits into one variety or hybrid. Often, these combinations help overcome weaknesses of certain traits. For example, combining brachytic dwarf with BMR helps reduce the lodging risk associated with BMR and increases the forage quality enhancement of shorter internodes in brachytic dwarf varieties.  FG

Bruce Anderson, Ph.D., is an agronomy and forage specialist for the University of Nebraska – Lincoln.

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