Chitinase Activity in Stylosanthes guianensis Systemically Protected Against Colletotricbum gloeosporioides

Three- and four-fold increases in chitinase activity were detected in the youngest, fully expanded leaf (L,)of Stylosanthes guianensis cw. Endeavour following inoculation of the second youngest, fully expanded leaf {U)with virulent Type B and Type A isolates of Colletotrichum gloeosporioides compared with chitinase activity in Li leaves of uninoculated plants. Only small increases in (3-1,3-glucanase were detected in L, leaves of systemically protected plants. Ghitinase activity was maximal in leaf L, 36 to 48 h after inoculation of leaf Lj, and this was coincident with the onset of resistance to anthracnose in L, leaves. Ghitinase activity also increased in L, leaves inoculated with a weakly pathogenic isolate of C. gloeosporioides. Resistance developed in these L, leaves to subsequent infection by a virulent isolate of the pathogen approximately 36 h after protectiveinoculation with the weakly pathogenic isolate. Two chitinase isozymes, with molecular weights of 65,000 daltons (pi 3.1)and 54,000 daltons (pi 4.0), were separated from extracts of G. g/oeosponoj(ies-challenged S. guianensis cv. Endeavour leaves. S. guianensis chitinase caused death of C gloeosporioides hyphae, particularly in the presence of ^-1,3-glucanase. Mycelial viability declined as activity of chitinase was increased in mixtures containing a fixed activity of/3-1,3-glucanase.