Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2001
Publication Date: 5/15/2001
Citation: Keinath, A.P., Farnham, M.W. Zool 2001. Effects of wirestem severity on survival and head production of transplanted broccoli and cabbage. Plant Disease. 85:639-643. Interpretive Summary: Broccoli and cabbage crops are commonly established by planting seed in trays followed by transplanting of resulting seedlings to the field. Transplantation and subsequent establishment of a productive crop are challenges in producing these vegetables. Typically, young seedlings have very tender tissues and are susceptible to stem and root rot fungi that can ndamage or kill them. It is not unusual for seedlings to become infected even before they are transplanted. Sometimes, transplants infected with fungal rot die in the field or become stunted and fail to produce any vegetable. In other cases, infection has no serious repercussions, plants outgrow the disease, and ultimately produce a harvestable vegetable at maturity. It would be useful if producers could know if seedlings with a given level of disease are likely to survive and produce and if using a given set of infected plants will result in a productive crop. Two-week-old dseedlings were purposely infected with a fungus called Rhizoctonia and disease was allowed to develop. Two weeks after inoculation, plants were rated for level of disease. Seedlings with high, intermediate and low levels of infection were transplanted to the field and survivability of plants two and six weeks after transplanting and head yield of plants at maturity were evaluated. In general, transplants with high levels of disease had very low survivability and produced few marketable heads. Transplants with low levels of disease exhibited good survivability and yield. These results show that low levels of infection should not significantly reduce stand and yield in transplanted broccoli or cabbage. This information should prove valuable to vegetable extensionists advising cole crop producers and to the producers themselves.
Technical Abstract: Field experiments were conducted with transplants of Brassica oleracea with known severity levels of wirestem, caused by Rhizoctonia solani anastomosis group 4. Seedlings of broccoli and cabbage were grown in steamed soil infested with 5 to 25 sclerotia/kg of R. solani. Two weeks after inoculation, plants were separated into five severity classes based on wirestem symptoms, then transplanted into fumigated field plots in the spring and fall of 1995. The percentage of plants with and without above-ground symptoms was assessed at 2 and 6 weeks after transplanting. Marketable-sized heads were harvested eight times. Percent symptomless plants, percent surviving (symptomless plus symptomatic) plants, and percentage of plants producing a marketable-sized head decreased as wirestem severity increased. In general, transplants of both crops with >75% stem girdling had lower percent survival and produced fewer marketable eheads than healthy transplants in both experiments. Percentage of plants producing a marketable-sized head was highly correlated (P=0.0001) with percent symptomless plants at 14 days after transplanting and percent surviving plants at 42 days after transplanting.