Differences in Susceptibility ofStylosanthes hamatatoColletotrichum gloeosporioides

Abstract

SONODA, R. M., and J. B. BROLMANN. 1980. Differences in susceptibility of Stylosanthes hamata to Colletotrichum gloeosporioides. Plant Disease 64:553-554. Anthracnose incited by Colletotrichum gloeosporioides was more severe on accessions of Stylosanthes hamata indigenous to the southeast coast of Florida with 2N=40 chromosomes than on those with 2N=20 chromosomes. The 2N=40 S. hamata were found in four localized areas and the 2N=20 ecotypes were widely distributed along the southeast coast of Florida. The 2N=40 accessions had a smaller beak on their seedpods and grew more vigorously in forage evaluation tests. Further tests are needed to determine whether the two types are conspecific. Stylosanthes hamata L. is indigenous to the southeast coast of Florida and to various areas in the Caribbean, Central America, and South America (7). It is one of several Stylosanthes spp. being tested as a forage plant in south Florida (2). One of the limiting factors in the use of Stylosanthes spp. is susceptibility to anthracnose incited by Colletotrichum gloeosporioides (Penz.) Sacc. (5). The C. gloeosporioides attacking Stylosanthes spp. in commercial and experimental plantings in Florida was probably introduced on contaminated seed (4). The pathogen was not found in surveys of native stands of S. hamata (10) along the southeast coast of Florida. Most of the S. hamata accessions collected from southeast Florida in the summer of 1979 were highly tolerant to C. gloeosporioides when inoculated (10). Three accessions were moderately susceptible (10). The most susceptible line was similar in pod morphology, ie, short beak, to an accession collected in 1971 that had excellent agronomic characteristics (2) but whose forage yield was reduced by C. gloeosporioides (6). The accession collected in 1971 had 2N=40 chromosomes, whereas most S. hamata accessions have 2N=20 chromosomes (3). A study was conducted to determine if differences in susceptibility of S. hamata indigenous to southeast Florida coincided with differences in chromosome number and pod morphology. MATERIALS AND METHODS Descriptions of S. hamata collected from native stands of the species from Fort Pierce, FL, south to Key West during the past 10 yr (approximately 200 collection sites) were searched for Florida Agricultural Experiment Stations Journal