Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/1999
Publication Date: N/A
Interpretive Summary: Seedlings of the cole crops cabbage, broccoli, and cauliflower are susceptible to a fungal disease called wirestem. This disease can kill the seedlings or damage the stem so that the plant remains stunted. Plants infected with wirestem typically fail to produce a harvestable vegetable and crop yields are reduced in disease-infested fields. This research was undertaken to determine if different strains and different forms of the fungus cause different levels of disease when they are artificially used to infect cabbage plants. Our goal is to gain the necessary information to develop a program for selecting resistant cultivars of cole crops. Results showed that one group of disease strains caused more disease than another group of strains. We also identified particular strains that were very damaging to plants and other strains that caused no disease. These results indicate that plant scientists can apply a preparation of a damaging strain to effectively evaluate plants for resistance to wirestem. This information will allow scientists to search for better levels of resistance than have currently been observed and to conduct systematic efforts to increase wirestem resistance through breeding. Ultimately, a farmer should be able to minimize crop losses due to wirestem and increase the profitability of cole crop production by choosing a resistant variety identified using an approach recommended by this research.
Technical Abstract: Three-week-old seedlings of cabbage cv. Bravo were inoculated with either infested cornmeal-sand cultures (91,000 colony-forming units per kg soil) or sclerotia (50 per kg soil) of one of ten isolates of anastomosis group (AG) 2-1 or 4 (five isolates each). Wirestem incidence (percentage of diseased and dead plants), severity on hypocotyls and roots (rated on a 1-10 scale), and plant fresh weight were assessed two weeks after inoculation. Wirestem incidence and severity were greater and plant weight was lower with cornmeal-sand inoculum than with sclerotial inoculum. As a group, isolates belonging to AG4 were significantly more virulent than those of AG 2-1. Within each AG, isolates could be separated based on virulence with either inoculum type. Use of sclerotial inoculum of a virulent isolate of R. solani AG 4 is recommended for future screening of cole crop germplasm based on uniformity of infection and ease of preparing and quantifying inoculum.