RECENT ADVANCES IN STUDIES OF ANTHRACNOSE OF STYLOSANTHES - I - THE BIOGEOGRAPHY OF STYLOSANTHES HAMATA, STYLOSANTHES-SCABRA AND STYLOSANTHES SEABRANA

Three species ''new'' to agriculture, viz. S. hamata allotetraploids, S. scabra and ''Stylosanthes seabrana'' have been recognised following the classification and evaluation of Stylosanthes collections, and cu ltivars have been developed. S. hamata is indigenous to the drier habi tats of the Caribbean Islands, southern Florida, Colombia and Venezuel a. Diploid (2n = 20) and allotetraploid (2n = 40) races are recognised currently. The diploids, from predominantly alkaline soils, require s pecific rhizobia from similar soils. The allotetraploids occur only in Colombia and Venezuela on acid-neutral soils and nodulate freely. S. scabra is an allotetraploid, widespread in South and central America. Accessions nodulate freely and show morphological and agronomic variat ion, which reflects the different geographic and climatic environments of their origin. ''Stylosanthes seabrana'' is a diploid closely relat ed to S. scabra originating from Bahia, Brazil. It has a specific Brad yrhizobium requirement, and occurs at altitudes of 400-1050 m in regio ns with 400-1190 mm annual rainfall and a 2-7 month dry season. This d iploid is a potential forage plant for northern Australia.