Heterodera trifolii associated with Fusarium root of Trifolium subterraneum in Northern Tunisia

Abstract

Larvae and cysts of species of Heterodera Schmidt were recovered from soil samples taken from the rhizosphere of subterranean clover, Trifolium subterraneum L., growing on experimental fields in the Ras Rajel, Sedjenane, and Grombalia-Cap Bon regions of northern Tunisia in 1974 and 1975. The samples were taken from sites where severe clover decline was detected (Fig. O. The diseased plants were often severely stunted and in most cases supported by a deformed and rotted, primary and secondary root system (Fig. 2). Several cultivars examined also exhibited various degrees of leaf reddening and to a lesser extent leaf chlorosis. Cysts were found on the roots of the Australian cultivars, Clare, Yarloop, Geraldton, Woogy, Mt. Barker, Woogenellup and on 11 Tunisian ecotypes. The number of cysts per 100 ml of soil ranged from 1 to 115 and the number of eggs and larvae per cyst between 80 and 120. The nematode was identified in Bonn as H. trifolii Goffart, 1932 and the identification verified by colleagues in Munster, Wageningen and St. Albans. The fact that populations of H. trifolii in New Zealand do not develop on the above mentioned cultivars indicates that a great deal of variation exists within the species (Yeates et al., 1972). This is believed to be the first report of this nematode causing economic damage to subterranean clover in the field and the first report of this nematode in Africa (Thomas and Taylor, 1968). Two species of Fusarium, F. oxysporum Schlecht ex Fr. and F. avenaceum (Fr.) Sacc., were consistently isolated from H. trifolii diseased plants. The rate of recovery seemed to be positively correlated with the presence and population density of H. trifolii. Both species of Fusarium are associated with a similar form of T. subterraneum decline in Australia (Kellock and McGee, 1972). The possibility that an interaction exists between H. trifolii and the two species of Fusarium is being studied. The author expresses his thanks to German Agency for Technical Cooperation, Ltd. for financial support and to the staff of INRAT Tunis, for technical support.