'Corchosis' of coffee in Costa Rica : A complex disease caused by Meloigogyne Arabicida y Fusarium Oxysporum

Coffee 'corky-root' disease, also called 'corchosis', was first detected in 1974 in a small area of Costa Rica where the root-knot nematode Meloidogyne arabicida is the dominant species. An epidemiological study revealed a constant Meloidogyne spp-Fusarium sp association in case of 'corky-root'. In parallel, there are apparently no cases of 'corky-root' reported in association with Meloidogyne exigua, which is the prevalent root-knot nematode on coffee in Costa Rica.The Fusarium spp. fungi are often cited as components of 'disease complexes' in association with nematodes. Combined inoculations of M. arabicida or M. exigua and Fusarium oxysporum under controlled conditions showed that only the combination M. arabicida with Eoxysporum can induce 'corky-root' symptoms on the roots of C. arabica cv. Caturra or cv. Catuai. E oxysporum alone was nonpathogenic. M. exigua or M. arabicida alone induced galls and reduction in shoot height but did not induce any 'corky-root' symptoms. Coffee varieties susceptible and resistant to M. arabicida were studied under field conditions for five years. All of the susceptible varieties exhibited corky-root symptoms on 40-80% of their root-systems. The resistant varieties which were resistant to M. arabicida but not to M. exigua did not show any corky-root development. These observations lead to the conclusions that 'corky-root' disease has a complex etiology and emphasizes M. arabicida's dominant role as a predisposing agent to subsequent E oxysporum invasions. Consequently, genetic resistance to M. arabicida appears to be an effective strategy against 'corky root' disease. (Résumé d'auteur