ABSTRACT
Summary The cerrados of the west central region of Brazil occupy 180 million ha and are classified as well-drained, tropical savannas. The Brazilian cattle population numbers 110 million, almost 60% of which is found in the cerrados. To improve the nutrition of the grazing animal, attention has been focused on cultivated pasture species, particularly tropical legumes. None of the commercial legume cultivars can be recommended for large areas of the cerrados. Species such as leucaena (Leucaena leucocephala [Lam.] de Wit) are not adapted to these acid, infertile soils with a high aluminum content, while Stylosanthes Sw. species are highly susceptible to the fungal disease anthracnose (Colletotrichum gloeosporioides Penz.). 185In 1978 an evaluation program was initiated to select legumes that (1) grow and produce seed on acid soils under aluminum and water stress, (2) persist under grazing, and (3) tolerate pests and diseases. The work is being conducted at the Cerrados Agricultural Research Center, near Brasilia, at lat 15°S and altitude 1,000 to 1,100 m. Annual rainfall is 1,500 mm, mostly distributed in a 6-month wet season, and mean annual temperature is 21°C. Nine hundred legume accessions from thirteen genera have now been established as spaced plants on the 2 major soil types of the region. The pH of the soils is 4.6, with aluminum saturation in excess of 70%. Known nutrient deficiencies were corrected. Results are reported for 352 of the accessions over a 2-year period. The most promising genus is Stylosanthes. Seventeen accessions of S. guianensis (Aubl.) Sw., S. capitata Vog., S. scabra Vog., and S. viscosa Sw. have combined good adaptation to acid soil conditions and good tolerance to pests and diseases. All S. guianensis accessions belong to a distinctive group of fine-stemmed, highly viscous ecotypes currently referred to as the “tardio” group. Their outstanding attribute is tolerance to anthracnose, the major limiting factor to the use of the genus in the region. Seed of the selected accessions is being multiplied for evaluation under grazing. The number of accessions of Stylosanthes has been increased further within the program. None of the other genera have shown the potential of the genus Sylosanthes. New Calopogonium Desv. and Galactia P. Br. accessions were no more productive than commercial control cultivars. Aeschynomene L. accessions were highly susceptible to anthracnose, while those of Pueraria DC., Teramnus P. Br., Vigna Savi, and Centrosema (DC.) Benth. species grew relatively poorly. Zomia J.F. Gmel. accessions were very vigorous, but all plants were very susceptible to an insect/virus/fungus complex. Tolerance has been found in new ecotypes of Z. brasiliensis Vog. Most Desmodium Desv. species showed poor vigor and were affected by the disease little-leaf mycoplasma. Observations are continuing with these other genera, but introductions are being made on a more limited scale.
