FUNGI ON ROOTS AND STEM BASES OF ASPARAGUS IN THE NETHERLANDS - SPECIES AND PATHOGENICITY

A survey was made to identify the most important soilborne fungal path ogens of asparagus crops in the Netherlands. Ten plants were selected from each of five fields with a young (1-4 y) first planting, five fie lds with an old (6-13 y) first planting and five fields with a young r eplanting. The analysis included fungi present in the stem base and th e roots of plants with symptoms of foot and root rot or showing growth decline without specific disease symptoms. Isolates of each species w ere tested for pathogenicity to asparagus on aseptically grown plantle ts on Knop's agar. Symptoms were caused by Fusarium oxysporum, F. culm orum, Botrytis cinerea, Penicillium verrucosum var. cyclopium, Cylindr ocarpon didymum, Phialophora malorum, Phoma terrestris and Acremonium strictum. F. oxysporum was by far the most common species and was isol ated from 80% of the plants. Not all of its isolates were pathogenic t o asparagus. Symptoms were caused by 67%, 78% and 93% of the isolates obtained from young first plantings, old first plantings and replantin gs, respectively. F. culmorum was isolated from 31% of the plants. Two other notorious pathogens of asparagus, F. moniliforme and F. prolife ratum, did not occur in our samples. Species causing symptoms in the v itro test that were found on more than 5% of the plants were additiona lly tested for their pathogenicity in pot experiments. F. oxysporum f. sp. asparagi caused severe foot and root rot, significantly reduced ro ot weights and killed most of the plants. F. culmorum caused lesions o n the stem base often resulting in death of the plant. P. terrestris, a fungus only once reported as a pathogen of asparagus, caused an exte nsive root rot, mainly of secondary roots that became reddish. The fun gus was isolated in only a few samples and is not to be regarded as an important pathogen in Dutch asparagus crops. P. malorum caused many s mall brown lesions on the stem base and incidentally also on the upper part of small main roots. This is the first report of its pathogenici ty to asparagus. The fungus is one of the organisms inciting spear 'ru st' and it reduced crop quality rather than crop yield. P. verrucosum var. cyclopium and C. didymum did not cause symptoms in pot experiment s. Because of its predominance on plants with foot and root rot and it s high virulence, F. oxysporum f.sp. asparagi was considered to be the main soilborne pathogen of asparagus in the Netherlands.