Craig Edminster2, Don Miller3, Jim Moutray4
IMPORTANCE OF ALFALFA
Alfalfa, called the "Queen of the Forages" is the fourth most widely grown crop in the United States behind corn, wheat, and soybeans. Although there is no published value for alfalfa hay the estimated value is $8.1 billion US. There are 23.6 million acres of alfalfa cut for hay with an average yield of 3.35 tons per acre. The estimated value of alfalfa hay is $102.50 per ton. Alfalfa meal and cubes are exported to other countries with a value of $49.4 million to the US economy. Alfalfa is sometimes grown in mixtures with forage grasses and other legumes. Mixed alfalfa and grass hay is harvested from 37.2 million acres annually. The acreage of all hay harvested including alfalfa per year is 60.8 million with an estimated value of $13.4 billion. When the value of alfalfa as a mixture with other forages is considered the acreage and value of hay is approximately equal to wheat and soybeans in the U.S.
Alfalfa is also important due to its high biomass production. The record yield of one acre of alfalfa is 10 tons/acre (22 Mg/ha) dryland and 24 tons/acre (54Mg/ha) with irrigation. Alfalfa is a widely adapted crop, energy-efficient and an important source of biological nitrogen fixation. The average acre of alfalfa will fix about 200 kg of nitrogen per year, thus reducing the need to apply expensive nitrogen fertilizers.
One of the most important characteristics of alfalfa is its high nutritional quality as animal feed. Alfalfa contains between 15-22% crude protein as well as an excellent source of vitamins and minerals. Specifically, alfalfa contains vitamins A, D, E, K, U, C, B1, B2, B6, B12, Niacin, Panthothanic acid, Inocitole, Biotin, and Folic acid. Alfalfa also contains the following minerals: Phosphorus, Calcium, Potassium, Sodium, Chlorine, Sulfur, Magnesium, Copper, Manganese, Iron, Cobalt, Boron, and Molybdenum and trace elements such as Nickel, Lead, Strontium and Palladium. Alfalfa is also directly consumed by humans in the form of alfalfa sprouts. According to the International Sprout Growers there are approximately $250 million dollars worth of sprouts sold annually in North America. Alfalfa juice is used in some health food products.
Alfalfa hay is used primarily as animal feed for dairy cows, but also for horses, beef cattle, sheep, chickens, turkeys and other farm animals. The value of milk, meat, wool and all other animal products is $132 billion, thus the total value of animal products plus the value of hay reach the $145 billion level. This far exceeds the combined value of all other high value crops.
In addition to the traditional uses of alfalfa as an animal feed, alfalfa is beginning to be used as a biofuel for the production of electricity, bioremediation of soils with high levels of nitrogen, and as a factor for the production of industrial enzymes such as lignin peroxidase, alpha-amylase, cellulase, and phytase.
Environmental concerns of erosion on cropland and use of pesticides suggest that greater acreage will be devoted to forage. The efficient conversion of forages into human foods by ruminants offers an excellent way of using the increased forage acreage and maintaining human food production. This conversion from plant to food and fiber is the basis of the beef, dairy and animal husbandry industry in North America. Alfalfa may well be one of the most complete feeds grown in North America. Its high quality nutrients have resulted in its being used in rations of ruminants, both young and old.
Protein: Alfalfa has one of the highest levels of digestible protein of any forage plant grown. Early cut (late bud, early-bloom stage) alfalfa hay may vary from 16 to over 20 percent protein. Even later cut alfalfa usually will contain at least 12-15 percent protein. The quality of alfalfa protein is excellent, with more than 70 percent of its total protein being digested. Alfalfa is also capable of producing large amounts of protein per acre. A per-acre yield of 5 tons of alfalfa harvested at the proper maturity will yield approximately 1800 pounds of protein per acre. That is equal to 2 tons of soybean meal to the acre!
Energy: Alfalfa is considered to be higher in feeding value than any other forage. It has always been perceived as an excellent source of protein, but is sometimes underestimated as an energy source. A ton of alfalfa hay contains as much total digestible nutrients (TDN) as 25 bushels of corn. Energy is necessary for weight gain, milk production and efficient calving. Some grass hays may analyze as high in digestible dry matter (DDM) as alfalfa, but those hays will not be digested as quickly. Alfalfa will pass through the rumen in about one-half the time as required by grass hay (36 vs. 70 hours). Therefore, animals fed alfalfa hay tend to gain faster, produce more milk and maintain themselves in better condition than those fed other forages.
Minerals: Alfalfa can provide most minerals and vitamins at less cost than if supplied from processed sources. If one pound of alfalfa hay is fed per 100 pounds of bodyweight, the beef or dairy cow will meet its daily requirements for calcium magnesium, potassium, sulfur, iron, copper, cobalt, manganese, zinc and selenium. Phosphorus levels of alfalfa are more moderate, but still high enough that if fed at the above rates will supply about 2/3 of the daily requirements needed. The high level of calcium in alfalfa is especially important for lactating cows, young developing replacement heifers and bulls.
Vitamins: Leafy, green alfalfa hay is unusually high in carotene the precursor of Vitamin A. Vitamin A is the most common beef and dairy cow vitamin deficiency. In addition to many dietary function of Vitamin A, this vitamin also may have some therapeutic values, and be a contributing factor in preventing "shipping fever complex" and other disorders associated with animal stress. Alfalfa is a good source of Vitamin E. "White muscle disease" which sometimes causes serious losses of calves is caused by a deficiency of Vitamin E. Sun-cured alfalfa hay is also a source of Vitamins D and K as well as riboflavin and niacin.
U.S. ALFALFA BREEDING HISTORY
INTRODUCTION OF ALFALFA IN NORTH AMERICA
Alfalfa is an immigrant to North America. It originated near Iran but related forms and species are found throughout central Asia. Alfalfa was brought to Europe and South America by invading armies, explorers, and missionaries as a valuable source of feed to horses Equus caballus and other animals. In 1850, Spanish types of alfalfa germplasm were introduced into the southwestern U.S. from South America. Between 1858 and 1910, three winter-hardy germplasm sources from Europe and Russia were brought into the upper Midwestern USA and eastern Canada. There were two intermediate winter-hardy introductions, one from Iran, Afghanistan and Turkey between 1898-1925 and the other from France in 1947. Non winter-hardy types were introduced from Peru (1899), India (1913 and 1956), and Africa (1924). Essentially all basic germplasm used in the development of present North American cultivars traces to these nine sources of alfalfa.
FALL DORMANCY OF ALFALFA
When alfalfa was first introduced into North America, it soon became apparent that not all alfalfas were alike. Some cultivars could survive the cold climate while other would not. When the source of these cultivars was examined, it was found that varieties originating from cold climates had better winter survival than the material imported from warmer climates. As a result of these observations, alfalfas were classified into two groups, winterhardy and non-winterhardy. Eventually these groups were subdivided, further.
With the expansion of alfalfa into numerous new areas and climates, the development and testing of new alfalfa cultivars increased. As the development of new alfalfa cultivars increased, it soon became more difficult to predict a given variety's winterhardiness because many different alfalfa lines were being crossed together.
As fast as new varieties were being released, this presented a problem to breeders on how to classify their new varieties for winterhardiness. It was not practical to wait around 4-5 years for a winter to be severe enough to sort out which varieties were more winterhardy. For this reason, breeders started looking for other characteristics as a means of predicting winter survival. Numerous cultivars traits were evaluated, such as depth of crown in the soil, size of crown; type of taproot branched or unbranched, etc. Finally a group of researchers noticed that photoperiod or day length and/or low temperatures triggered the majority of winterhardy varieties to quit growing early in the fall. In broad terms, the winterhardy varieties were preparing for winter by shutting down their growth activity and conserving their root reserves to survive the winter. Non-hardy plants were not affected by shortening day length, and/or lower temperatures and they continued to grow abundant top growth in the fall. Therefore, these non-hardy populations often suffered repeated frost damage and eventually depleted their root reserves, making winter survival less probable.
Based on this information alfalfa breeders now had a new means of predicting winter survival. This was not a direct measurement of winter survival, but a prediction based on whether or not a cultivar grew or did not grow top growth late in the fall. This system was later refined in which nine classification or subdivisions of alfalfas were identified based on long term data of check varieties. A graduation of plant height in the fall was established using check varieties. Cultivars in class "1" had little or no top growth in the fall, and were represented by the variety Norseman. Cultivars in class "9" had very tall plant growth and were represented by the variety CUF 101. Nine gradations of fall dormancy were then associated with check varieties based solely on plant height. Cultivars that had the same height as CUF 101 were then classified as having the same dormancy as CUF 101 or fall dormancy of 9.
FALL DORMANCY RATING (pre NAIC 1998)
1=Norseman (cold climates)
9=CUF 101 (warm climates)
FALL DORMANCY RATING (post NAIC 1998)
1=Maverick (Norseman) (cold climates)
3=Pioneer 5446 (Ranger)
11=UC-1465 (warm climates)
This system of using fall dormancy (plant height in the fall) was very useful for a number of years. However, now there is a movement among breeders to further refine the system. Breeding efforts in the past 15-20 years have vastly improved the disease and insect resistance of alfalfa varieties to a point that they are harder to kill in the field. For this reason, moderately winterhardy and non-hardy varieties are now surviving harsher winter conditions than their fall dormancy rating normally indicates. Fall dormancy 5's are now being used where 4's were in the past; 4's are being used where 3's were in the past and so on for all dormancies. The associated yield increase from the more non-dormant material has fueled this trend of using less dormant materials.
This trend has now resulted in breeders describing their varieties in new ways such as " This variety has fall dormancy rating of 5, but the winter survival of a 4". This actually means that the breeder feels the variety has the yield potential of a 5 (with later fall growth), but will survive winter conditions generally associated with a 4. Future descriptions of alfalfa varieties will have fall dormancy rating (based on plant height in the fall) and winter survival ratings based on actual winter survival data.
ALFALFA SEED PRODUCTION
Alfalfa seed is primarily grown in the northwestern areas of the U.S. primarily in the western states of California, Idaho, Nevada, Oregon, Wyoming, and Washington. The approximate yield of alfalfa seed in 1999 for the U.S. is 115 million pounds, with average price of $190 per 100 pounds of seed, thus the estimated value of alfalfa seed is $218.5 million dollars. A fringe benefit to the production of alfalfa seed is the production of honey from bees. In the U.S., $147.7 million dollars worth of honey is produced each year.
DISEASE, INSECTS AND NEMATODES
Alfalfa disease, insects and parasitic nematodes can significantly reduce yields, stand life, and forage quality. It is estimated that over 25% of the U.S. alfalfa hay crop is lost to pest damage annually. This accounts for an estimated $2.5 billion dollar loss annually to the industry. Reduction in farm revenues can be avoided in most cases by using a few common sense approaches. Selection of high yield disease resistant cultivars in combination with proven cultural practices can minimize potential losses. Knowledge of the conditions that promote disease buildup and the ability to recognize the symptoms of each major pathogen or nematode is a substantial tool in being successful in alfalfa hay production.
5 MAJOR DISEASES
Bacterial Wilt - Clavibacter michiganense subsp. insidiosum
Optimal disease conditions - Occurs in cooler northern regions during second or third crop year.
Symptoms - Yellowish-brown discoloration in the woody cylinder of the taproot. Scattered plants become stunted, yellow-green in color.
Control - Resistant varieties
Fusarium Wilt - Fusarium oxysporum
Optimal disease conditions - Can occur in most soil types but damage can be more severe in the presences of nematodes or root feeding insects that create sites for entry into root system.
Symptoms - Stunting of plants; red to reddish brown discoloration inside the root that becomes more severe with age of stand.
Control - Resistant varieties; root knot nematode resistance may also be desirable to complement Fusarium wilt resistance by reducing exposure of the plant to the pathogen by nematode feeding on the roots.
Phytophthora Root Rot - Phytophthora megasperma
Optimal disease conditions - Occurs most often in soils with poor drainage where water stands for an extended amount of time.
Symptoms - Stunting and/or plant death in low areas of fields where water stands. Damaged plants may have taproot girdled at same depth in soil.
Control - Resistant varieties; cultural practices that promote better drainage i.e. deep plowing, laser leveling, planting on beds.
Anthracnose - Colletotrichum trifolii
Optimal disease conditions - Occurs most often in spring or fall and spreads rapidly under warm wet conditions from spores produced on lower stems of infected plants.
Symptoms - Early stages may appear as individual straw colored stems on plants that display a curved top "Shepherds Crook". Diamond shaped lesions will occur on lower part of the stem. Advanced stages will be seen in the crown tissue as a dark black or coal color. Plant death usually occurs at this stage.
Control - Resistant varieties; avoid spreading spores from plant debris on harvest equipment to uninfected fields.
Verticillium Wilt - Verticillium albo-atrum
Optimal disease conditions - Thought to occur only in cooler northern climates until it was identified in the late 1980's in parts of Southern California. The pathogen can be spread by dry or fresh plant material on harvest equipment. Cutter bar blades of mowing equipment are extremely effective in spreading the pathogen spores from diseased fields to healthy fields.
Symptoms - Stunting of plants; yellow "V" shape at the tip of leaves. Leaves may curl along midrib and turn a pinkish color. Stems will remain green after leaves die.
Control - Resistant varieties; clean farm equipment between fields, and mow younger fields before older to prevent spore transfer on mower blades. Cutter bar sanitation with 10% bleach may be useful.
5 MAJOR INSECTS
Potato Leafhopper - Empoasca fabae
Symptoms - Alfalfa yellowing. Feeding of these "jumpy" insects causes severe stunting of the plants and yellowing or reddening of the foliage. Leafhopper damage starts in wedge shaped areas at the tips of the leaves. First cut is not usually affected, but subsequent cuttings may be severely damaged.
Control - Resistant varieties
Alfalfa Weevil - Hypera positica
Symptoms - Most important insect pest of alfalfa in the U.S. Damage from this insect usually starts in early spring when the larvae emerge. The young larvae have black heads and a white stripe down the back. They feed first in the growing tips and then shred the foliage, giving infested fields a grayish cast. The adults are about ¼ inch long and usually are not seen during the day. The pupae may be found in net-like cocoons either on the plants or in debris on the soil. Both larvae and adults are present after the first cutting, feeding on new growth. Remaining larvae soon mature and the new adults leave the fields during the summer, but return in the fall and start depositing eggs.
Control - No resistant varieties commercially available. Biological control agents (parasitic wasps and a fungus) have greatly reduced the impact of the alfalfa weevil in the eastern regions of the country.
Pea Aphid - Acyrthosipon pisum
Symptoms - This large green aphid is common on alfalfa. It builds up huge populations, which cover the stems and terminal buds in cool, wet seasons. It causes damage by sucking plant juices, causing the plants to wilt. Usually, as drier and warmer weather develops, natural controls reduce the infestations. This insect has many natural enemies.
Control - Resistant varieties
Spotted alfalfa aphid - Therioaphis maculata
Symptoms -This tiny aphid is light yellowish green or straw colored, with rows of dark spots on its back. Unlike the pea aphid, it develops under hot, dry conditions. It causes severe stunting and yellowing of plants and will kill seedling stands. It secretes a great abundance of sticky honeydew in which a sooty black fungus may develop. This aphid is most severe in the arid areas of western and southwestern United States.
Control - Resistant varieties
Blue aphid - Acyrthosiphon kondoi
Symptoms -The blue alfalfa aphid was first found in California in 1974 and now occurs in several western and midwestern states. It is similar to the pea aphid in appearance, but can be distinguished by its bluish green coloration in contrast to the yellowish or light green color of the pea aphid. Coloration of the third antennal segment of adults and nymphs and thoracic area of the winged forms can also be used in the field. The third antennal segment of the blue alfalfa aphid is uniform brown in contrast to a narrow dark band at the tip of the third antennal segment in the pea aphid. The thoracic area of the winged pea aphid is light brown, in contrast to a dark blackish brown for the blue alfalfa aphid.
Control - Resistant varieties
3 MAJOR NEMATODES
Stem - Ditylenchus dispsaci
Conditions that promote nematode damage -
- Sandy soil
- Cool moist spring or fall
- Sprinkler irrigation
- Susceptible plant or weed hosts
- In the spring or fall, sporadic white stems or "white flags" may be seen throughout the field.
- Stunting in somewhat circular patterns in the field
- Swollen stem buds
- Shorten internodes and swollen nodes on lower stems
- In advanced stages lower stem may blacken
- Fewer symptoms seen during summer months
Control - Resistant varieties or rotational with a grain crop for 3 years
Root Knot - Meloidogyne
Northern - M. hapla
Southern - M. incognita
Columbia - M. chitwoodi
Conditions that promote nematode damage -
- Sandy soil
- Nematode infection may increase severity of some root diseases such as Fusarium wilt
- Stunting in somewhat circular patterns in the field
- Stand reduction
- Excessive root branching and small galls on roots
- Resistant varieties
- Crop rotation is generally not feasible due to wide host range
Root lesion - Pratylenchus penetrans
Symptoms - Above ground symptoms include stunting and nutrient deficiencies. Root lesion nematodes reduce root growth and inflict black or brown lesions on the root surface. Lesions may fuse to cause the entire root to appear brown. Secondary infections of roots by other bacterial or fungal pathogens commonly occur after invasion.
Control - Crop rotation, fallow, nematicide or resistant varieties (Archer II FD=5)
Many other disease and insects may in fact limit alfalfa production and/or
negatively effect quality of alfalfa hay. They include but are not limited to:
Aphanomyces Root Rot - Aphanomyces euteiches
Alfalfa blotch leaf miner - Agromyza frontella
Alfalfa dwarf/Pierces disease - Vitis vinifera
Alfalfa mosaic virus - Alfalfa mosaic virus
Alfalfa snout beetle - Brachyrhinus ligustici
Alfalfa wart - Urophlytis alfalfa
Blister beetles - Epicauta species
Common leaf spot - Pseudopziza medicaginis
Cloverleaf weevil - Hypera punctata
Clover Root Curculio - Sitona hispidulus
Crown Rot Complex (Combination of Fusarium, Pythium, Rhizoctonia, Phoma and Stagonospora)
Differential Grasshopper - Melanopus differentialis
Downy Mildew - Peronospora trifoliorum
Lepto leaf spot - Lepto sphaerulina briosiana
Meadow spittlebug - Philaenus spumarius
Plant bugs - Lygus species
Pythium - Pythium species
Rhizoctonia - Rhizoctonia solani
Rust - Uromyces striatus
Sclerotinia crown and stem rot - Sclerotinia trifoliorum
Spring Black Stem - Phoma medicaginsis
Stagnospora root rot - Stagonospora meliloti
Stemphylium leaf spot - Stemphylium botryosum
Summer black stem - Cerespara medicaginsis
Yellow leaf blotch - Leptotrochila medicaginis
Witches Broom - Witches Broom
Variegated cutworm - Peridroma saucia
From the time alfalfa was first introduced into North America by immigrants there has been a progressive effort to improve its performance. In the early years this effort was minimal and farmers were satisfied with just knowing what alfalfa would survive on their farms for more than one year. This was reflected in the fact that prior to 1955 only 33 alfalfa cultivars were recognized in the U.S. and Canada, half of which were plant introductions. As time progressed farmers soon discovered that if their alfalfa operation was to remain profitable, better alfalfas were needed. The first effort to improve alfalfa, beyond winter hardiness, was disease resistance. The success of the first varieties with disease resistance and their ability to increase yields and profitability caused a large demand for continued improvements, and by 1977 the number of improved alfalfa varieties increased to 160. Today there are over 300 improved alfalfa varieties being marketed in the U.S. Much of the improvement of alfalfa has been in the area of increased resistance to diseases, insects and nematodes. Today, alfalfa breeding programs routinely breed for 10 distinct dormancy groups and screen for resistance to 5 diseases, 4 insects, and 4 nematodes, in addition to increased forage yield, persistence, and quality. This increased pest resistance has resulted in higher yields and stand persistence in areas where these pests are limiting factors.
The improvements in alfalfa cultivars in the last 25 years have been mainly in the areas of persistence and yield (forage and seed). These genetic improvements have been, for the most part, indirect improvements, since yield and persistence were not selected for directly, but obtained by incorporating higher and higher levels of multiple pest resistance. By reducing yield losses due to an ever-increasing list of pests, higher average yields and increased persistence was obtained over time. Breeders in cooperation with the North American Alfalfa Improvement Conference (NAAIC) and Alfalfa Council have developed a series of standardized tests that can be conducted in growth chambers, greenhouse or in the field. These standardized tests provide a format to properly characterize alfalfa cultivars for marketing purposes (Fig. 3). Standard tests may include plant culture protocol, inoculum culture, inoculation procedure, incubation, rating scale, check cultivars for resistance and susceptibility, source of inoculum, scientists with expertise, correlation to field reaction, races, culture options and alternative methods.
WHAT RESISTANCE MEANS IN ALFALFA
Often there is much confusion over what is actually meant by the term resistance, when used in association with alfalfa varieties. Due to the complex genetic makeup and breeding behavior of alfalfa, breeders have modified the use of the word. Many farmers are familiar with the term resistant in association with other crops in which all the plants of a variety are genetically identical, or uniform, as in the case of hybrids or self-pollinated crops. In this case every individual plant carries resistance in the variety. Alfalfa varieties are different in the sense that every plant within a variety is genetically different.
Some plants in a variety may be resistant while others are susceptible. For this reason alfalfa breeders are forced to describe their varieties based on the average performance of all the individual plants in the variety. Therefore, the term resistant has been subdivided into several groupings based on the percentage of individuals displaying resistance within a variety. The term "high resistance" (HR) describes a variety that has 51% or more of its plants exhibiting resistance. A graduation of resistance (Fig. 1) is used to describe 5 distinct categories with the last being "Susceptible" (S) in which 5% or less of the plants exhibit resistance.
HR = High resistance
R = Resistance
MR = Moderate resistance
LR = Low resistance
S = Susceptible
This rating system is used by alfalfa breeders across the U.S. and is utilized by the NAAIC Variety Review Board in conjunction with its standardized testing procedures in describing alfalfa varieties. At first glance these levels of resistance would appear to be insufficient to provide adequate protection under field conditions, since even a resistant variety has a significant level of susceptible plants. However, repeated studies have shown that each level of resistance displays an appreciable level of benefit that is statistically different from the others. One proposed explanation of this field performance is that the resistant plants are randomly distributed throughout the field in such manner that interrupts the spread of the pathogen (Fig.2). Therefore, a resistant variety needs only 31-50% resistance to effectively disrupt the effect of a pathogen and display significant economic advantage.
Figure 2 - Diagram of resistance levels on field plantings of alfalfa
ALFALFA VARIETIES OF THE 9O'S
Alfalfa development in the last twenty-five years has increased substantially. Most of the emphasis of variety improvement in the 70's and 80's was in the area of pest resistance. Multiple pest resistance provided the framework for improved yield, persistence and quality. These increased levels of pest resistance were for known pests or to new ones such as verticillium wilt in the 70's and aphanomyces in the 80's. Tremendous amounts of resources were and still are committed to development of increased pest resistance in new varieties. However, large yield improvements due to increased pest resistance are now harder to obtain. Adequate resistance levels for most major pests of alfalfa have been obtained and only moderate yield gains are expected with increased resistance to secondary pests.
Alfalfa breeders in the late 1980's began focusing on new ways to improve their varieties. The development of pest resistance was at its peak. Development of multileaf or multifoliate varieties in the late 1980's was one of the first new areas of development. As a result, there has been a renewed interest in the area of "quality" and most breeding programs have made this a new and important criterion for variety development. Different companies are approaching the quality issue in several ways.
Other areas of variety development being used by alfalfa breeders are as follows:
OUR VISION OF THE FUTURE - ALFALFA IN THE FUTURE
Cebeco International Seeds and ABI alfalfa's research and development efforts continue to provide the most advanced traits and characteristics available today- varietal discoveries that add value for your customers and business.
Seed, service and solutions.
1Presentation at the first China Alfalfa Development Conference. China Grassland Society, Beijing Agriculture Committee. May 10-14, 2001.
2Vice President of Marketing, Cebeco International Seeds, Inc.
3Senior Plant Breeder, ABI Alfalfa Inc.
4Director of Research, ABI Alfalfa Inc.