Early decline of asparagus in the Netherlands : etiology, epidemiology and management

Asparagus plants on fields cropped with asparagus before establish well but economic life of the crop is only half of that on fresh land. Fusarium oxysporum f.sp. asparagi was identified as the main cause of this early decline. Autotoxic compounds were detected in residues of asparagus roots even 11 years after the crop was finished but evidence for a role of these compounds in the etiology of the disease was not obtained. The pathogen was found on asparagus seed, on one-year-old crowns used as planting material and was isolated from soil, frequently even from fields without an asparagus history. In inoculation experiments, the pathogen caused severe root rot in asparagus, mild root rot occasionally in pea and lupin, and it colonized the roots of many plant species that did not show symptoms. Twenty-four isolates of the pathogen were assigned to 18 vegetative compatibility groups indicating the large genetical diversity of the population in the Netherlands. The potential of nonpathogenic isolates of F. oxysporum to reduce severity of Fusarium root rot was shown in growth chamber and greenhouse tests but not when plants were grown in the field for one year. A new method for reducing soil infestation with Fusarium oxysporum f.sp. asparagi and other soilborne pathogens was developed. It is based on induction of fermentative soil conditions. When fresh broccoli or grass was incorporated into soil that was subsequently irrigated and covered with plastic mulch, oxygen in soil was rapidly depleted and redox potential (Eh) reached values as low as -200 mV. After 15 weeks, populations of F. oxysporum f.sp. asparagi , Rhizoctonia solani , Verticillium dahliae , and Globodera pallida were strongly reduced in inoculum samples buried in soil demonstrating the potential of this approach to control a range of soilborne pathogens