Tunisia: The impact of farming systems and culture on Fusarium diseases of cereals.

A knowledge of local farming systems and culture is critical to an understanding of the epidemiology of diseases caused by soil-borne fungal pathogens and the development of management practices. Fusarium diseases are no exception. Studies by the senior authors have shown that Fusarium foot
and root rot (FFRR) caused by F. culmorum is the dominant Fusarium disease of wheat and barley in Tunisia where durum wheat is the major cereal. Crown rot caused by F. pseudograminearum is a minor problem. This contrasts to Australia where crown rot is the dominant Fusarium disease of wheat and barley in most areas. Tunisia has a typical Mediterranean climate – AAR varies from 700 mm in the north to 300 mm on the southern margin of the main grain belt. The rainfall is reasonably reliable in the north and less reliable in
the central and southern areas where late stress is common leading to whitehead formation in plants affected by FFRR. The practice of small-holder sheep herders having the traditional right to heavily graze stubbles is a key factor contributing to the dominance of FFRR. This unique feature of the farming system is deeply embedded in the culture of the region where wheat has been grown for over 2000 years. Furthermore the
demand for baled straw for drought feeding in the arid grazing areas of the south-central region is such that there is little scope for adopting stubble retention practices without significant social upheaval in rural areas. Tunisia is a small country with 6M sheep and desertification continues to adversely affect the rangelands on the fringe of the Sahara. The paucity of cereal residues means there is minimal carryover of the crown rot
pathogen as it persists mainly as hyphae in residues. However F. culmorum can also persist in soil as chlamydospores that presumably form abundantly in infected root systems. Consequently this pathogen has an effective mode of persistence in the absence of residues. While the adoption of direct seeding per se is unlikely to affect inoculum levels, the retention of stubble residues would significantly increase inoculum levels and yield loss. The authors are investigating the impact of various rotations on inoculum levels through temporal
studies at permanent reference sites in commercial fields and field trials.