POSSIBILITIES OF CROSS-PROTECTION AGAINST FUSARIUM WILT BY NON-PATHOGENIC ISOLATES OF FUSARIUM F.SP. DIANTHI
The intensity of the effects depended on the period between pre-inoculation with the non-pathogenic isolates and the inoculation with the pathogenic isolate and on the concentration of both the non-pathogenic and pathogenic isolates.
The best effects were seen when the time interval was c. 7 days. Pre-inoculation with a suspension of spores of 106 spores per ml was more effective then with a suspension of 103 spores per ml. After inoculation with a suspension of 103 spores per ml of the pathogenic isolate fewer plants were attacked than after inoculation with a suspension of 106 spores per ml. After one year, disease percentages were 15–30 compared to 100 in the non pre-inoculated treatment after a half year.
Experiments on rooting cuttings in a substrate, to which spores of non-pathogenic isolates of F. oxysporum f.sp. dianthi were added, were not succesfull. No roots were formed. Only when the medium was drenched with a solution of spores one week after the start of the rooting period cuttings with a normal root system were obtained. The non-pathogenic F. oxysporum could be isolated from the plants.
The pre-treated rooted cuttings were planted in lightly contaminated soil or in steamed soil, which was inoculated later, after different intervals, with a pathogenic isolate of F. oxysporum f. sp. dianthi. The pre-treated plants were attacked at a later stage and to a lesser extent than non pre-treated plants.
The results of the experiments indicate a process of cross-protection. More research however has to be done to incorporate this process of partial control into the whole complex of Fusarium wilt control.