Proc. 56th Southern Pasture and Forage Crop Improvement Conference, Springdale, AR April 21-22, 2001
Forage Legume Breeding and Evaluation at Auburn University
in the Last 16 Years.
Jorge A. Mosjidis
mosjija@auburn.edu
The breeding program on forage legumes at Auburn University has two main objectives, namely, basic research and development of new cultivars for use as forage and cover crops. Species we work with in cultivar development are sericea lespedeza [Lespedeza cuneata (Dumont de Courset) G. Don], vetches (Vicia spp), crimson clover (Trifolium incarnatum L.), caley pea (Lathyrus hirsutus L.), red clover (Trifolium pratense L.), and white clover (Trifolium repens L.). The more basic research objectives are 1) to identify and evaluate physiological, morphological and molecular traits that can be used as selection criteria in developing germplasm of forages with enhanced persistence, tolerance to environmental stress, yield, seedling vigor and disease resistance; 2) to study population genetics, genetic structure and genotype-environment interactions to formulate selection strategies conducive to the development of improved germplasm through conventional and unconventional breeding techniques; and 3) to assist the National Plant Germplasm System (NPGS) in the evaluation, maintenance and collection of germplasm of forage legume species. Research on topics 1, 2 and 3 has been conducted in red clover, vetches and sericea lespedeza.
Due to the limited space available, I will present only our major accomplishments in cultivar development and selected research on some factors limiting the use of some of the species that we are working with or on breeding methodology. Research on issues of importance to NPGS will not be presented.
Sericea lespedeza.
This long-lived species is well adapted to most of the southeastern U.S. and can provide much needed forage during the summer in the Southeast region. It tolerates low soil fertility and acidity and droughts common to the southern region. Also, it sheds the lower leaves during the growing season to form a protective mat on the soil surface. This leaf litter decomposes to form a valuable source of organic matter and nutrients (Kalburtji et al., 1999). A field with a four year stand of sericea lespedeza grown for soil conservation or biomass production may have about 7600 kg ha-1 of dry matter residues on the surface. Fletcher and Livingston (1949) reported that sericea lespedeza increased total porosity, enlarged the volume of noncapillary pores, increased both the surface water infiltration rate and subsurface transmission rate, and increased air flow rate of eroded soils. The main problems, perceived or real, that limit the use of sericea lespedeza are (1) low palatability due to high tannin content in fresh forage, (2) low forage quality, (3) difficulty in establishing the crop because of poor seedling vigor.
Findings regarding low palatability. There are no palatability problems with hay. Furthermore, a study conducted on low and high tannin plants showed that polyphenols (tannins) are located in vacuoles of paraveinal mesophyll cells that function in photosynthate transport within the leaf. This finding suggested that these substances play an active role in physiological processes of sericea lespedeza plants. It was determined that even very young leaves (1/4 of the final size) and stems of high tannin genotypes had a high level of condensed tannins (Mosjidis et al. 1990), a particular type of polyphenols associated with low palatability. However, field observations indicated that cattle would eat the first few inches from the top of the stems of those high condensed-tannin genotypes suggesting that tissue maturity has more effect on palatability than tannin content.
Findings regarding low forage quality. Assessment of forage quality within the canopy of sericea lespedeza indicates large strata effects on leaf and stem composition for all traits measured except lignin which had the same value across strata (Table 1). Values of NDF, ADF, cellulose, and hemicellulose increased from the top of the stem to the base whereas protein content was reduced. Leaf and stem quality in the top 20 cm (about 8″) was very good.
Findings regarding crop establishment. There are striking difference in germination between fresh seed, unhulled seed stored in a controlled-climate warehouse (about 15C and 55 % relative humidity), and hulled seed stored under ambient conditions prevalent in the Southeast. Storing conditioned seed at ambient conditions severely reduces germinability (Mosjidis 1991). Lower germination is detrimental to the establishment of sericea lespedeza.
Seedling vigor of sericea lespedeza was found to be limited by temperature during germination and by temperature and daylength after emergence (Mosjidis 1990). This research indicated that current planting date recommendation are suboptimal from the point of view of the physiology of sericea lespedeza plants, i.e., the crop should not be established immediately after the last frost as currently recommended but rather several weeks later when the soil temperature is adequate. Optimum germination is 20-30 C (Qiu et al., 1995). However, finding optimum conditions for establishment is easier said than done because soil moisture is another major factor in crop establishment and it is well known that good soil moisture in the Southeast is more likely in early Spring when temperature is suboptimal for the plant. In summary, sericea lespedeza is a risky crop to establish because all the environmental conditions needed for good establishment are difficult to find in the Southeast. Optimum temperature for seedling growth was determined to be 26-30C and 13 h daylength (Mosjidis 1990).
In summary, the forage quality results discussed above indicated that it was important to graze or clip sericea lespedeza when the stems are not too long (10-12″ tall) to reduce palatability problems and to obtain the best quality forage possible. These findings also indicated that there was a need for a sericea lespedeza that could tolerate grazing better than the available genotypes what agreeded with the long standing view to improve grazing tolerance in sericea lespedeza. Consequently we developed the cultivar AU Grazer. Establishment problems can be reduced by using fresh seed of good quality.
Table 1. Leaf and stem composition of sericea lespedeza as affected by canopy strata.
|
NDF |
ADF |
Protein |
Lignin |
Cellulose |
Hemicellulose |
|
|
————————————- g kg-1————————— |
||||||
| Leaves in Strata
Top 10 cm |
338 |
257 |
232 |
52 |
192 |
82 |
| Stems in Strata
Top 10 cm |
456 |
352 |
181 |
68 |
274 |
103 |
Cultivar releases. ‘AU Grazer’, released in 1997, is the first sericea lespedeza cultivar tolerant to grazing (Mosjidis 2001). This cultivar has higher survival and more vigor under grazing conditions than other sericea lespedeza cultivars. Stems are fine and pliable. Field testing under mob grazing (about 80 head of beef cattle were placed in the field for 3-5 days) showed that the populations that make up this cultivar had 50% more stems on average (an indication of survival ability) than the leading cultivar Serala in 1997, the year following mob grazing.
‘AU Donnelly’, a low-tannin cultivar released in 1987 (Mosjidis and Donnelly 1989), has more early spring growth and is higher yielding throughout the season than AU Lotan, the only other low-tannin cultivar commercially available. AU Donnelly averages 6% higher in digestible dry matter and 10% higher in crude protein than AU Lotan at the hay stage. Tannin content is about the same in AU Donnelly as in AU Lotan.
Crimson clover.
It is one of the best species to use as a cover crop because of high early season biomass production and associated N content. The main objectives of the breeding program have been earlier forage growth, increased biomass yield and selection of different flower color types for the horticulture industry. We are currently selecting a pink-flowered type.
Cultivar releases. ‘AU Sunrise’, released in 1997, is the earliest maturing crimson clover cultivar in the market. It was selected and released in cooperation with Mr. Charles M. Owsley and Mr. Malcolm Kirkland, USDA-Natural Resources Conservation Service (NRCS), (Mosjidis et al. 2000). AU Sunrise flowers 5 to 18 days earlier than AU Robin and 12 to 28 days earlier than Tibbee. It is well-adapted to Alabama and Georgia and has been grown successfully in Texas.
Hairy vetch.
Hairy vetch is a cold tolerant species well adapted to most of the USA where it is widely grown as a forage and cover crop. Most of the work done at Auburn University has been on cultivar development. The main objectives of the breeding program have been early maturity and improved biomass and seed yield.
Cultivar releases. ‘AU Merit’, released in 1999, is a hairy vetch (Vicia villosa L.) cultivar that, on average, has a forage yield 4-12% higher than common hairy vetch and flowers on average 7-13 days earlier than the common type; depending on location and year it can flower up to 24 d earlier.
‘AU EarlyCover’ is the only early flowering hairy vetch cultivar commercially available. It was released in cooperation with Mr. Charles M. Owsley and Mr. Malcolm Kirkland, USDA-NRCS, in 1994 (Mosjidis et al. 1994, 1995). AU EarlyCover flowers 23 to 36 days earlier than common hairy vetch. Crude protein content of AU EarlyCover is about 27% (dry matter basis) on or near April 1 in Alabama and Georgia. AU EarlyCover is an excellent cover crop because of its early growth. When this cultivar is harvested or incorporated into the soil as a green manure crop on or around April 1 (about the time when many farmers in the lower South are ready to plant corn), dry matter yield is comparable or superior to common hairy vetch. In many cases, AU EarlyCover could also be a better choice for forage than common hairy vetch. Hairy vetch is commonly used as a legume companion with small grains that is to be cut for silage or hay. AU EarlyCover will work better in such situations because its early maturity (and thus the optimum harvest date) better matches that of the small grains. If hairy vetch is to be used for pasture, AU EarlyCover would be a better choice when early grazing is desired.
Auburn University cooperated in the release of the hairy vetch cultivar ‘Americus’ by the Georgia Agricultural Experiment Station and the USDA-NRCS in 1993 (Surrency et al. 1995).
Common vetch.
Common vetch (Vicia sativa L.) is less winter hardy than hairy vetch which limits the area where it can be grown as a winter crop. However, resistance to some nematodes can be found in common vetch germplasm whereas resistance to nematodes has not been found in hairy vetch. Breeding of common vetch has focused on improved earliness, biomass and resistance to the root-knot nematode [Meloidogyne arenaria (Neal) Chitwood] and soybean cyst nematode (Heterodera glycines Ichinoe), the most important nematodes in the southeastern region of the U.S.A. We are currently field testing lines that are resistant to Meloidogyne arenaria race 2 and Heterodera glycines race 4.
Caley pea.
Caley pea, also called wild winter pea, singletary pea, or roughpea, is a cool-season annual legume introduced from the Mediterranean region. For many years this plant has been used in the southeastern U.S.A. as a livestock forage as well as a cover crop despite the fact that no cultivars have been commercially available. When farmers have been able to locate a commercial source of seed, it has most commonly been a mixture of vetch and caley pea.
Caley pea is mostly grown on heavy clays of the lower Mississippi Delta and on calcareous clays of the Alabama and Mississippi Black Belt areas where it is superbly well adapted and has readily reseeded. Caley pea can be successfully grown in areas too wet or too calcareous for most annual clovers, but is also tolerant of mildly acid soils. It is useful as a temporary ground cover and green manure crop on land which is to be replanted to another crop in mid to late spring, as a source of nitrogen and spring forage in johnsongrass [Sorghum halepense (L.) Pers.] and dallisgrass (Paspalum dilatatum Poir.) hayfields or pastures, and as a wildlife food plant. Hard seed coats allow natural reseeding when stands are not heavily grazed during the seed production period.
Cultivar releases. ‘AU GroundCover’, is the only caley pea cultivar available in the market. It was released in cooperation with Mr. Charles M. Owsley and Mr. Malcolm Kirkland, USDA-NRCS, in 1994. AU GroundCover yielded as much forage as commercial hairy vetch in yield trials (Mosjidis et al. 1994, 1996).
Red clover.
This short-lived perennial legume that is productive for a year in central and southern Alabama but remains productive for about three years in the Blackbelt area and for two years in the northern part of the state. Red clover can be overseeded into cool or warm season perennial grasses or planted in a pure stand. Although is low yielding early in the season (Feb.- March) when other forages have high biomass production, it has the potential to provide high levels of good quality forage throughout summer and often into the fall season. The main objectives of the breeding program are improved persistence and high biomass yields. We are currently field testing improved populations.
From the breeding point of view, one of the most important results from our research on red clover is that knowledge of the correlation between juvenile and mature plant traits is critical in determining the opportunities for early stage selection. We determined that red clover plants and families with low potential yield can be eliminated at the seedling stage. Furthermore, using selection index updating (a method of multistage selection) we determined that early culling at the seedling stage resulted in significant cost savings and increased gain to cost ratio. These results will allow breeders to increase the number of superior plants to be field tested or conduct a more rigorous evaluation of selected plants. This represents a major improvement in breeding methodology for forages, red clover in particular. Among five selection schemes tested for direct selection of mature plant traits, mass selection produced the largest genetic gain. Also, a good correlation between some seedling traits and mature plant performance was found in common vetch and sericea lespedeza.
White clover.
This is a productive species widely adapted to the Southern region that produces good quality forage through early summer. The breeding program has focused on improving persistence especially under grazing conditions, better establishment into a thick sod, drought tolerance and high biomass yields. We will soon field test populations selected for improved persistence and establishment.
References
Fletcher, P.W. and R.B. Livingston. 1949. Structure improvement following legume growth on unfertilized subsoil. Soil Sci. Soc. Am. Proc. 14:347-350.
Kalburtji, K.L., J.A. Mosjidis, and A.P. Mamolos. 1999. Litter dynamics of low and high tannin sericea lespedeza plants under field conditions. Plant and Soil. 208:271-281.
Mosjidis, J.A. 1990. Daylength and temperature effects on emergence and early growth of sericea lespedeza. Agronomy Journal 82:923-926.
Mosjidis, J.A. 1991. Effect of seed processing, storage condition, and genotype on viability of sericea lespedeza seed. Seed Science and Technology 19:623-626.
Mosjidis, J. A. 2001. Registration of ‘AU Grazer’ sericea lespedeza. Crop Science 41:262.
Mosjidis, J.A. and E.D. Donnelly. 1989. Registration of ‘AU Donnelly’ sericea lespedeza. Crop Science 29:237-238.
Mosjidis, C.O’H., C.M. Peterson, and J.A. Mosjidis. 1990. Developmental differences in the location of polyphenols and condensed tannins in the leaves and stems of sericea lespedeza, Lespedeza cuneata. Annals of Botany 65:355-360.
Mosjidis, J. A., C. M. Owsley, M. S. Kirkland, and K. M. Rogers. 1995. Registration of ‘AU EarlyCover’ Hairy Vetch. Crop Science 35:1509
Mosjidis, J. A., C. M. Owsley, M. S. Kirkland, and K. M. Rogers. 1996. Registration of ‘AU GroundCover’ Caley Pea. Crop Science 36:207.
Mosjidis, J. A., C. M. Owsley, M. S. Kirkland, and K. M. Rogers. 2000. Registration of ‘AU Sunrise’ Crimson Clover. Crop Science 40:290.
Qiu, J., J.A. Mosjidis, and J.C. Williams. 1995. Variability for temperature of germination in sericea lespedeza germplasm. Crop Science 35:237-241.
Surrency, D.S., C.M. Owsley, M.S. Kirkland, D.V. McCracken, P.L. Raymer, W.L. Hargrove, J.L. Day, and J.A. Mosjidis. 1995. Registration of ‘Americus’ hairy vetch. Crop Science 35: 1222.
Xie, C. and J.A. Mosjidis. 1995. Seedling selection effects on morphological traits of mature plant in red clover. Theoretical and Applied Genetics 91:1032-1036.