Etiological and Epidemiological Aspects of Dry Root Rot in Nurseries and Orchards in Tunisia

摘要

Fusarium spp. are found commonly in the soil of citrus orchards and nurseries. Symptomless infections can occur during seedling production in the nursery and they progress in fruit bearing plants causing dry root rot. Studies were carried out to assess the Fusarium spp. population and its seasonal variation in three Tunisian citrus nurseries and on three different citrus rootstocks (sour orange, Troyer and Carrizo citranges). Monitoring was also carried out under field conditions to study the incidence of dry root rot in Tunisian orchards. Based on morphological and molecular characterization, three Fusarium species were isolated from Tunisian citrus nurseries; F. solani (Mart.)Sacc, F. oxysporum Schlechtend; Fr. and F. proliferatum (Matsush.)Nirenberg. Fusarium spp. populations varied according to the rootstock, the season and the management. In fact, a significant increase in Fusarium spp. populations was related to temperature increase, root activity, soil mix composition, irrigation method, and fertilization. A positive correlation (r=0.74) was observed between Fusarium population in the soil and the degree of fibrous root infection. Specific symptoms of dry root rot were observed in the field on very few citrus trees. Based on these results, dry root rot in Tunisian citrusgrowing activities seems not to be a current threat since almost all citrus varieties are grafted onto sour orange rootstock.