Relative susceptibilities of five fodder radish varieties (Raphanus sativus var. Oleiformis) to Meloidogyne chitwoodi

The fodder radish varieties Anaconda, Contra, Defender, Doublet and Terranova, known to have some partial resistance, were compared to the standard variety, Radical, to estimate their relative susceptibility (RS) for both population dynamic parameters of Meloidogyne chitwoodi and to evaluate Pi dependency. This approach must eventually lead to new screening methods for partial resistance tests. Plants were grown under controlled glasshouse conditions. Twelve densities of nematodes in five replications were used. Five plants per 7 l pot were allowed to grow for a period of 11 weeks until their early flowering stage. Few seedlings of all the varieties at Pi=32 and 64 J2 (g dry soil)-1, and all seedlings exposed to the highest density, Pi=128 J2 (g dry soil)-1, died within a week after germination. Replanted seedlings developed into normal plants. Total yield, expressed as total fresh weight, was not affected by M. chitwoodi. A lower percentage of plants with galls was observed on partially resistant varieties as compared with Radical. For Radical, a maximum multiplication rate (a) of 0.38 and a maximum population density (M) of 6.43 J2 (g dry soil)-1 were estimated. Radical proved to be a bad host for M. chitwoodi with all final populations lower than the Pi. The parameter estimates of (M) for Anaconda, Contra, Defender, Doublet and Terranova were 0.011, 0.006, 0.027, 0.020 and 0.009 J2 (g dry soil)-1, respectively. With Radical taken to be 100% susceptible, this resulted in RSM values of 0.17, 0.10, 0.42, 0.32 and 0.14% of these varieties, respectively, reducing high population levels of M. chitwoodi by more than 98%. There was no correlation between the rMgalls and the RSM values, indicating that scoring the number of galled plants will not provide a suitable measure for partial resistance