Evaluation of Popcorn Cultivars as Resistant Rotation Crops to Columbia Root-knot Nematode A Systems Approach

This study examined the management situation for the Columbia root-knot nematode (Meloidogyne chitwoodi) in potato, using an approach with systems thinking and interactive meetings. The focus of current research for control of this nematode was evaluated. Control practices include crop rotation, and this study also evaluated popcorn cultivars for their potential as resistant rotation crops. Popcorn cultivars were grown in M. chitwoodi race 1 infested soil at the Hermiston Agricultural Research and Extension Center (HAREC), Hermiston, OR. Soil samples were taken soon after planting (initial) and before harvest (final), and the number of M. chitwoodi juveniles / 250 g dry soil was calculated for each sample. A reproduction index was calculated for the nematode reproduction on each cultivar: R value = initial / final population. Cultivars were categorized as good, poorand nonhosts depending on their R values. Popcorn cultivars were also tested for their host status in the greenhouse. Plants were inoculated with approximately 5000 M. chitwoodi eggs (initial), and after 55 days, eggs were extracted from the roots (final). In the field and greenhouse tests, field corn (FC) cv Pioneer 3578 was tested as a good host check. Among cultivars tested in both the field and greenhouse, the seven with the lowest R values as % of FC 3578 were: WOC 9508 (4%), W206 (16%), WOX 9512 (23%), Robust 33-77 (30%), Robust 20-70 (38%), and WOC 9504 (42%). Cultivars more susceptible than field corn were (R values as % of FC 3578 mean of field, greenhouse tests): W 104 (119%) and Robust 90477 (102%). Popcorn cultivars WOC 9531, WOC 9556, WOX 9528, and WOX 9511 were more resistant than field corn but still need to be also tested in the field. Cultivars with R values < 1.0 in field tests can be functional in decreasing or stabilizing nematode populations, thus increasing the effectiveness of prepotato nematicides or winter cover crops. This nematode pest situation was analyzed with use of diagrams showing interacting components of the system. This system includes people, nematodes, and potatoes. Issues and questions emerged as the situation was viewed in a systems manner. Some of these issues and questions were the foci of a Farmer-Scientist Focus Session conducted on June 28th, 1995 in Hermiston, OR. Participants included growers, researchers, and extension educators. The meeting was interactive and facilitated the expression of ideas, perspectives, and concerns of the crop rotation possibilities for controlling M. chitwoodi. The opportunities and challenges using non-host crops in potato rotations were discussed. Growers expressed desire for more agronomic information about currently available poorand non-host cultivars. They did not emphasize a need for a more diverse selection of resistant cultivars. From the grower's perspective, the main opportunity of resistant crop rotation is the integration of suppressive winter cover crops. The main challenge is the small market size for most non-host crops. Additional interactive meetings are needed to stimulate the creation of new ideas and to refine the vision and direction of research in a cooperative manner.