Reaction of sugar beet S1 lines and cultivars to different isolates of Macrophomina phaseolina and Rhizoctonia solani AG-2-2IIIB

Interactions of 17 sugar beet lines and cultivars with four isolates of Macrophomina phaseolina (the causal agent of charcoal rot) and one isolate of Rhizoctonia solani (the causal agent of crown and root rot) were studied in separate experiments under greenhouse conditions. The isolates of Macrophomina were taken from their host plants, sugar beet (two isolates), soybean and sesame. In the first experiment, the colonized toothpick was used as inoculum. In the second experiment, six-month-old sugar beet plants were inoculated with barley seeds colonized with M. phaseolina. For the inoculation of sugar beet lines with R. solani, the colonized corn seeds were used. Root symptoms were recorded four weeks after inoculation, by estimating the proportion of the root surface infected by the pathogens, using a 1-9 standard scale. Our results showed a significant difference among lines and cultivars in their resistance to these two pathogens. Line B8618 was found to be considerably resistant to the isolates of the both pathogens. The inoculation methods of Macrophomina isolates had no significant effect on the results. The interaction between isolate and cultivar was not also significant in Macrophomina-resistant lines. Therefore, it appears that the response of sugar beet lines to the tested fungal isolates was not differential. These resistant lines showed a high resistance to all the tested M. phaseolina isolates. Our results revealed that the Macrophomina-resistant lines also showed resistance to R. solani. Furthermore, the sugar beet drought tolerant lines (M293, M362 and M345) were susceptible to the tested M. phaseolina and R. solani isolates.