Fusarium Yellows of Celery
This infosheet was originally authored by R.F. Cerkauskas, Agriculture Canada and M.R. McDonald, University of Guelph. It was reviewed by Janice LeBoeuf, Vegetable Crop Specialist, OMAFRA.
Table of Contents
Fusarium yellows of celery is caused by a soil-borne fungus called Fusarium oxysporum f.sp. apii which causes disease symptoms only on celery and which may result in serious yield and quality losses in infested fields. Historically, this disease caused extensive losses to celery growers from about 1920 until the late 1950s when a resistant celery cultivar, Tall Utah 52-70, was introduced. Many of the subsequent resistant cultivars were descendents of Tall Utah 52-70 and the disease was no longer a threat until a new race of the fungus appeared in California in the 1970s. Since then, race 2 of Fusarium oxysporum f.sp. apii has been reported in Michigan, New York, Texas, and in 1988, it was first observed in Bradford, Ontario.
The fungus infects the plants through the root system. The severity of the disease in the field is closely associated with the degree of infection of the plants. Early infection, such as at time of sowing or transplanting, often leads to more severe yield and quality losses than infection later in the season near the time of harvest. Other factors, such as the soil population levels of the spores, and the weather during the growing season are also important. For example, as the population of these spores increases in the soil, more severe symptoms develop, while the disease appears most severe during warm seasons, and on heavy wet, soils.
Symptoms due to mild or late infections consist of slight stunting, a stiffening of the outer stalks or petioles, and a brown discoloration of the vascular system where water and food materials are transported. The leaves generally become more brittle, with a rougher texture, and curl upward. In severe infection, the outer leaves become yellow first (Figure 1) and the yellowing spreads to other leaves as the disease progresses through the vascular system of the roots and crown. In later stages of disease development, the foliage turns brown and dies (Figure 2).
The distribution of plants with symptoms in affected fields may appear to be patchy since not all plants are affected with the same severity. The fungus is spread when infested soil is carried from affected fields to disease-free fields by farm equipment such as on tractor tires or other farm implements, or on the shoes of field workers. It may be introduced also by use of infested seedling transplants. The fungal spores may be disseminated short distances when flood water containing soilborne spores moves from the higher parts of an infested portion of the field to the lower sections of the disease-free part of the field. Long distance dissemination occurs by windblown soil containing the fungus inoculum.
The fungus persists in soil for many years as dormant spores in the absence of celery, or by colonizing the roots and stems of nonsusceptible host such as sweet corn, cabbage, and especially carrots. The roots of many weeds such as lamb's-quarters, smartweed, barnyard grass, and purslane are colonized also, but remain symptomless and allow the fungus to multiply, thereby increasing the population in the soil in the absence of the celery crop. Thus, short-term fallowing of infested fields is not an effective control measure, and research has demonstrated that even low spore populations in the soil may cause crop failures at harvest. Spore populations of the fungus increase quickly if susceptible celery cultivars or carrots are grown in infested fields. Continuous celery production, and incorporation of celery trimmings back into the soil at harvest will greatly increase spore populations and enhance disease development in the subsequent celery crop since the discarded celery material serves as a food source for the fungus. Rotation with onions or lettuce prevents spore populations in soil from increasing as quickly as with the susceptible celery crop so that after 2 or 3 years moderately resistant celery cultivars may be re-introduced into infested fields and disease severity reduced.
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