Arachis glabrata (PROSEA)
Arachis glabrata Benth.
- Protologue: Linn. Soc. London, Trans. Bot. 18: 159 (1841).
- Family: Leguminosae
- Chromosome number: 2n= 40 (tetraploid)
Arachis prostrata Benth. (1841).
- Rhizoma peanut (Am).
Origin and geographic distribution
A. glabrata and its near relatives are native to Brazil, Argentina and Paraguay in a large triangular area between 13°S and 28°S. Over the last 50 years, various sets of the group have been sent to Australia and the United States, and more recently to India, Thailand, Malaysia and Indonesia.
Although A. glabrata is primarily used as a high quality forage legume for intensively grazed pastures on infertile, acid soils, it also has potential for soil conservation and as an ornamental. It has proven useful for hay production in Florida, and is showing promise under coconuts in Indonesia.
In the United States, in vitro organic matter digestibility (IVOMD) values ranging from 45-68%, and N concentrations from 1.6-2.9%, have been measured in DM from stands cut twice a year. Up to 74% IVOMD and 3.5% N have been measured from stands cut every two weeks. In Australia, IVOMD of 6-week-old regrowth of seven accessions varied from 70-77% with N varying from 2.5-3.5%. Phosphorous levels in the DM largely reflect soil P levels, and have been measured from 0.15% in A. glabrata growing in extremely infertile soils to 0.52% in well-fertilized soils.
Herbaceous perennial with erect to decumbent unbranched, hollow above-ground stems 5-35 cm long, 2-3 mm thick, arising from a mat of rhizomes which range in thickness from 3-5(-10) mm. Rhizomes which form a dense mat in the top 5 cm of soil arise from the deep, woody taproot; roots covered with a multitude of small, oblate nodules. Leaf glabrous to sparsely pubescent, tetrafoliolate; leaflet ranging from linear-lanceolate to oblanceolate, obovate or cuneate up to 4 cm × 2 cm; apex acute to mucronate, base mostly obtuse; petiole grooved, up to 7.5 cm long, 1-2 mm diameter with pulvinus 10-15 mm above axil; stipules linear-lanceolate, falcate, up to 3 cm long, adnate to the petiole and membranous below the pulvinus; petiolule about 1 mm and rachis 10-15 mm long. Flowers sessile, axillary; hypanthium filiform, tubular, up to 10 cm long, pilose, containing the ovary at its base; standard more or less orbicular, 15-25 mm wide, yellow, soft orange to brilliant orange without red veins on back. Fruit set geocarpic, but usually scarce; fruit ovoid ca. 10 mm × 5-6 mm. Seeds ovoid, whitish.
Growth and development
Because seed set is rare, A. glabrata is usually propagated from rhizomes. With adequate temperature and moisture, shoots usually emerge 2-3 weeks after planting; dense swards develop as rhizomes form and extend the margins of the stand at up to 2 m per year in the absence of competition, or 5-30 cm per year with grass competition. Accessions differ in rate of spread. Despite often dense flowering, few seeds are set, except in some accessions prior to dense sward development. Seedlings are usually quite large before they form rhizomes.
Other botanical information
Although not validly published according to the International Code of Botanical Nomenclature, there is a system of classification in common use which divides the genus Arachis L. into a number of sub-generic sections and series, based largely on the diversity of growth habits within the genus. Section Rhizomatosae Krap. & Greg. (nom. nud.) which comprises the rhizomatous types is divided into series Prorhizomatosae Krap. & Greg. (nom. nud.) and Eurhizomatosae Krap. & Greg. (nom. nud.). The former is a group of delicate diploids, the latter is a group of more robust tetraploids of which A. glabrata is a member. In the absence of current description, it is not clear which of the 100 extant representatives of the Eurhizomatosae actually belong to A. glabrata . The foregoing description of A. glabrata was drawn from a diverse set of Eurhizomatosae . Four cultivars of A. glabrata have been released in Florida: "Arb", "Arblick", "Florigraze" and "Arbrook". "Arb" and "Arblick" were selected initially, based on productivity and spreading ability respectively; "Florigraze" was selected because it combined both characteristics, and "Arbrook", the most recent release, because it is more drought-tolerant than "Florigraze" but is of similar productivity. One accession known as the Maiwa peanut (probably the Australian accession CPI 12121) has persisted well in Indonesia.
A. glabrata is productive from about latitudes 30°N and°S to near the equator. It has persisted in areas receiving rainfall as low as 750 mm per year but is probably best suited to areas receiving 1000-2000 mm. It grows successfully on soils with textures ranging from sands to clays provided they are well-drained. While apparently preferring acid soils, it has produced good yields on neutral to slightly alkaline soils. It grows well on soils low in P. Unlike many tropical legumes, A. glabrata can compete successfully with sward-forming grasses such as bahia grass ( Paspalum notatum Flueggé), narrowleaf carpet grass ( Axonopus affinis A. Chase), pangola grass ( Digitaria eriantha Steudel) and bermuda grass ( Cynodon dactylon (L.) Pers.).
Moderate to heavy grazing pressures are necessary for best performance. It grows best when mean monthly temperatures are above about 20 °C. Although tops are cut by frost, plants regrow vigorously with the onset of warmth and moisture. During very dry conditions, top growth may die off, but rhizomes mostly survive, providing a nucleus for recovery.
Propagation and planting
A. glabrata is best propagated from rhizomes. While pieces of rhizome as short as 5 cm may strike, it is generally considered best to plant 30 cm square pieces of rhizome mat about 1.8 m apart. Alternatively, the rhizomes can be teased out, broadcast over the soil surface and disked in. In either case, it is best to plant about 3.5 m3of rhizomes/ha at a depth of 3 cm in clay soils to 6.5 cm in coarse sands. It is generally not necessary to inoculate rhizomes. A clean seed-bed is preferable, to minimize competition for the developing plants. Ideally, rhizomes should be produced in sandy soils for ease of digging. Planting appears to be most successful when rhizomes are dormant.
Weeds should be controlled during establishment. This can be achieved through manual weeding or through use of pre- and post-emergence herbicides such as trifluralin or vernolate, post-emergence applications of alachlor and dinoseb, and routine applications of bentazon or 2,4-DB for broadleaf weed control, and sethoxydim and fluazifopbutyl for grass control, as required. Mowing reduces shading from taller weeds and promotes spread of A. glabrata . A dressing of P fertilizer may be advisable if soils are extremely low in P. However, liming is rarely necessary.
Diseases and pests
A. glabrata is rarely troubled by insects or disease. It is immune to the common groundnut leaf-spots caused by Cercospora arachidicola and Cercosporidium personatum , and most accessions are immune to groundnut rust ( Puccinia arachidis ). Although susceptible to other leaf-spots caused by Phyllosticta and Stemphylium , and to white mould ( Sclerotium rolfsii ), these diseases have not caused serious long-term damage. Resistance to root-knot nematodes ( Meloidogyne spp.) has been recognized in a number of studies.
Low-growing accessions are best used in grazed pastures. Taller-growing accessions also lend themselves to hay-making or cut-and-carry systems.
Dry matter yields of up to 16 t/ha have been measured in Florida and up to 12 t/ha in Australia. Yields of only 5 t/ha have been obtained in Malaysia and Indonesia, but these may have been influenced by shading from rubber and coconuts.
Large collections are held by various germplasm banks at Texas A & M University (Stephenville, United States) and North Carolina State University (Raleigh, United States), at CENARGEN/EMBRAPA (Brasília, Brazil) and at ICRISAT (Patancheru, India). A more limited set is held at ATFGRC (CSIRO, Australia) and QDPI (Gympie, Queensland, Australia).
"Florigraze" is the result of a chance intra-specific cross in Florida. While A. glabrata is compatible with species from sections Arachis and Erectoides Krap. & Greg. (nom. nud.), the resultant hybrids are infertile. An intersectional rhizomatous hybrid, more productive than either parent, has been developed in Tamil Nadu, India.
A. glabrata is a persistent, very productive, high-quality forage, well-adapted to the often infertile, acid soils and heavy grazing pressures encountered in the humid and sub-humid tropics and subtropics. The main constraint to evaluation and adoption is the need to propagate from rhizomes. With the development of mechanical methods or with the availability of manual labour for propagation, A. glabrata may prove to be one of the more useful forage legumes in South-East Asia.
- Gregory, M.P. & Gregory, W.C., 1979. Exotic germ plasm of Arachis L. interspecific hybrids. The Journal of Heredity 70: 185-193.
- Gregory, W.C., Gregory, M.P., Krapovickas, A., Smith, B.W. & Yarbrough, J.A., 1973. Structure and genetic resources of peanuts. In: Wilson, C.T. (Editor): Peanuts - culture and uses. A symposium. American Peanut Research & Education Association, Inc., Stillwater, Oklahoma, United States. pp. 47-133.
- Prine, G.M., Dunavin, L.S., Glennon, R.J. & Rouch, R.D., 1986. "Arbrook" rhizoma peanut, a perennial forage legume. University of Florida, Gainsville. Agricultural Experiment Station Circular S-332. 16 pp.
- Prine, G.M., Dunavin, L.S., Moore, J.E. & Rousch, R.D., 1981. "Florigraze" rhizoma peanut, a perennial forage legume. University of Florida, Gainsville. Agricultural Experiment Station Circular S-275. 22 pp.