Phytotoxic and cross-protective effects of culture filtrate of Rhizoctonia solani isolates on Zea mays

The present study was undertaken to examine the phytotoxicity of culture filtrates of R. solani isolates Udm, Del, Dho, Rch, Mtp and Bpn on the seed germination and seedling growth of Z. mays. Cross protection by weak pathogenic isolates was also examined against the most pathogenic isolates in the study. The findings revealed significant variability in phytotoxicity of the culture filtrates of 6 isolates on seed germination, seedling growth and severity of disease symptoms; the isolates Udm and Del being the most aggressive on the host and also in macroscopic interactions with other 5 isolates. However, when maize seeds were pretreated with culture filtrates of 6 isolates, the aggressiveness of Udm and Del was reduced. Severity of symptoms by Del was most effectively reduced compared to Udm. Mtp isolate showed best result in cross protection, reducing the severity of symptoms to 53% for Udm and 50% for Del isolate. However, seeds pretreated with Udm and Del isolates also showed a slight reduction in severity of symptoms. This reveals that increased concentration of the culture filtrate in pretreatment of maize seeds may provide better cross protection against the same R. solani isolate infecting the host. The study highlights the use of culture filtrate as biotic stress for screening of resistant germplasm, which can save manpower, expenses, and time.