Arachis pintoi (PROSEA)
Arachis pintoi Krap. & Greg., nom. nud.
- Protologue: In: Wilson, C.T. (Editor): Peanuts - culture and uses: 121 (1973). Leguminosae
- Chromosome number: 2n= 20
- Pinto peanut (En)
- Thailand: thua lisong tao.
Origin and geographic distribution
Pinto peanut originates from the valleys of the Jequitinhonha, Sao Francisco and Tocantins rivers in central Brazil. Since its collection in 1954, it has been distributed to Argentina, Australia, Colombia and the United States, and more recently to many countries in South-East Asia, Central America and the Pacific.
Because of its high degree of shade tolerance, pinto peanut is finding application as a pasture legume in tree plantations, but also as a ground cover in plantations from which grazing animals must be excluded. It is showing potential in intensively managed grass/legume pastures on cleared land.
In vitro digestibility of pinto peanut varies from 60-76%, N concentrations from 2.5-3.0% and P concentrations from 0.18-0.37%. It is well accepted by cattle at all stages of growth. There are 6-8 seeds in pod/g.
A stoloniferous, perennial herb developing a strong taproot on the older crowns and large numbers of small oblate nodules, mostly to 2 mm diameter, on both taproot and subsidiary roots. Stems initially prostrate, becoming ascendant to 20 cm height in dense swards. Leaves tetrafoliolate, margins entire, ciliate; distal leaflets obovate and proximal leaflets oblong-obovate, obtuse at the apex and slightly cordate at the base; leaflets may attain 4.5 cm × 3.5 cm, but are smaller in regularly defoliated stands; the upper surface of leaflets is glabrous and a darker green than the pubescent lower surface. Flowers emerge individually from short axillary racemes and are similar in shape to commercial groundnut ( A. hypogaea L.), but smaller (standard 12-17 mm wide) and yellow. The terminal pod on the peg usually contains a single seed but may contain 2, while pods formed along the peg contain only one. Pod moderately reticulated, 10-14 mm × 6-8 mm, containing mostly a single seed. Seed light-brown, 8-11 mm × 4-6 mm, weighing 0.11-0.20 g.
Growth and development
Seedlings of pinto peanut develop quickly following epigeal germination, and with good growing conditions and several plants per square metre, complete ground cover can be achieved by a network of stolons in less than six months. Flowering commences three to four weeks after emergence and continues through the growing season, appearing to intensify following rain or irrigation. The ovary is borne on a gynophore or peg, which elongates to up to 27 cm after pollination and pushes the ovary up to 7 cm depth into the soil. Seed remains viable in the ground for more than one season.
Other botanical information
The genus Arachis L. has been divided into a number of invalidly published sections based on growth form and gross morphology. A. pintoi is one of two species in the section Caulorhizae Krap. & Greg., (nom. nud.), a section defined by the possession of stolons. The original line collected by G.C.P. Pinto near the mouth of the Jequitinhonha River in 1954 and variously catalogued as GK 12787 (Collection Number), PI 338314 (United States), CPI 58113 (Australia) and CIAT 17434 (Colombia), has been released as cultivar "Amarillo" in Australia. More recent collections of the species differ slightly from the original in leaf shape and size, and internode length.
The climate in central Brazil is humid tropical, with some 1800-2000 mm of rain falling in the October-May wet season, and an additional 200 mm in the June-September dry season. Pinto peanut has been mostly collected in red, sandy-loam alluviums, apparently growing best in low areas which are wet to flooded during the wet season. Soils are generally of low fertility with high Al content. Native vegetation is low forest with a fairly dense canopy. In cultivation, pinto peanut has proven adaptable to soils ranging from sand to clay texture, with low to neutral pH and low to high fertility. It failed to persist on seasonally waterlogged, poorly structured clays. In pot experiments, it has shown a tolerance of soil Mn at levels detrimental to many other legumes, a fair tolerance of soil Al, and a low tolerance of salinity. It is capable of growing under shaded conditions, often appearing more vigorous in shade than in full sunlight.
Propagation and planting
Fresh seed of pinto peanut has a high level of dormancy which may be reduced by drying the seed at 35-40 °C for 10 days. Seed should be inoculated with a specific strain of Bradyrhizobium, which is different from that used on commercial groundnuts. A well-prepared seed-bed is desirable but not essential. Seed should be sown 2-6 cm deep at 10-15 kg seed in pod/ha, followed by rolling. If seed is not available, pinto peanut is readily propagated from cuttings.
Pinto peanut is tolerant of and increases under heavy grazing, but, under light grazing, is not shaded out by taller grasses. It does not require highly fertile soil, but on an oxisol in Colombia it responded to additions of P, K, Ca and Mg.
Diseases and pests
The only information available relates to "Amarillo", which is resistant to the major groundnut diseases, rust ( Puccinia arachidis ) and leaf-spot ( Mycosphaerella spp.). Other fungi ( Phomopsis sp., Cylindrocladium sp. and Colletotrichum gloeosporioides ) have been isolated from leaf-spots, the latter also being associated with black stem lesions in Colombia. None of these diseases causes long-term or serious damage. "Amarillo" has moderate to high resistance to the various root-knot nematodes ( Meloidogyne spp.) but is susceptible to the root-lesion nematode ( Pratylenchus brachyurus ). Leaves of some plants have an apparently non-pathogenic variegation. Rats and mice are attracted to the nuts and can be a problem in stands of pinto peanut.
Being a low-growing, ground cover species, pinto peanut is more readily grazed than hand-harvested. Seed should be dried in the sun or in an artificial drier and stored under cool conditions with low humidity.
In Colombia, pinto peanut had an annual DM production ranging from 5 t/ha growing with Brachiaria dictyoneura (Fig. & De Not.) Stapf, which produced 20 t/ha, to 10 t/ha when grown with B. ruziziensis Germain & Evrard, which produced 11 t/ha. It has yielded 5 t/ha of DM in pure stands under 30% shade in Indonesia and 3 t/ha in full sunlight in Malaysia. Yields of seed in pod from 1-2 t/ha have been recorded.
A number of accessions have been collected, most of which are held by CENARGEN/EMBRAPA in Brazil. A more limited range is held at Texas A & M University (Stephenville, United States), CIAT (Colombia), and ATFGRC (CSIRO, Australia).
Breeding mechanisms are well understood, since Arachis wild types have largely been collected as a source of genetic material in groundnut improvement programmes, but there are no breeding programmes.
Pinto peanut has only been assessed as a forage over the last 10 years. At this stage it appears to have great potential in the wet tropics, especially in more shaded situations under plantation crops.
- Cook, B.G. & Franklin, T.G., 1988. Crop management and seed harvesting of Arachis pintoi Krap. et Greg. nom. nud. Journal of Applied Seed Production 6: 26-30.
- 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 and Education Association Inc., Stillwater, Oklahoma, United States. pp. 47-133.
- Grof, B., 1985. Forage attributes of the perennial groundnut Arachis pintoi in a tropical savanna environment in Columbia. In: Proceedings of the XV International Grasslands Congress, August 24-31, Kyoto, Japan. Science Council of Japan and Japanese Society of Grassland Science, Nishinasuno, Japan. pp. 168-170.
- Lascano, C.E. & Thomas, D., 1988. Forage quality and animal selection of Arachis pintoi in association with tropical grasses in the eastern plains of Colombia. Grass and Forage Science 43: 433-439.
- Oram, R.N., 1990. B. Legumes 21. Arachis (a) Arachis pintoi Krap et Greg. nom-nud. (Pinto peanut) cv. Amarillo. Australian Journal of Experimental Agriculture 30: 445-446.
- Valls, J.F.M., 1983. Collection of Arachis germplasm in Brazil. Plant Genetic Resources Newsletter 53: 9-14.