Control of fusarium wilt of cucumber by chemical and biological agents

Abstract

The main goal of the study was to search for potential pesticide alternatives for the control of Fusarium wilt of cucumber. Biological control and induction of systemic acquired resistance by chemical and biological agents were the logical choices. The results of the investigation are presented in four separate chapters. Each chapter approached the same problem from a different angle. In the first chapter, the nature of the potential of pesticide pollution was emphasized in the future of disease control. A thorough literature review concerning various aspects of modern control methods is presented. In chapter two, the induction of systemic acquired resistance in cucumber by various agents was investigated. Isonicotinic acid as a chemical agent and Pseudomonas cepacia as a biological agent proved to be the most effective inducers among the five tested. P. cepacia had the greatest effect on hyphal growth and fungal sporulation among all the agents. P. cepacia was able to cause severe deformities in four test pathogens. Isonicotinic acid as a chemical inducer, did not have a similar effect but was able to significantly suppress infection of cucumber seedlings by Fusarium oxysporum f. sp. cucumerinum. Both isonicotinic acid and P. cepacia were able to delay the initial onset of wilt disease and to significantly reduce disease incidence in all test cucumber cultivars either as a stem injection or as a root dip treatment. The third chapter focuses on various possible mechanisms for control of Fusarium wilt in cucumber by nonpathogenic isolates of F. oxysporum f. sp. cucumerenium. Isolate N1 was able to delay the appearance of wilt symptoms. When the time between introduction of N1 into root system and challenge to the system with wilt pathogen was increased the plants had a better opportunity to build up their resistance and reduce infection. Seventy-two days after inoculation of plants previously treated with N1 or C14 (a nonpathogenic isolate) the plants had a mortality ratio of 30, and 55, respectively compared to the 94% of unprotected plants. Various etiological and pathological methods were evaluated in chapter four. A protocol for screening Trichoderma and Gliocladium isolates to select the most efficient one is proposed. Twenty-seven Trichoderma spp. and nine Gliocladium spp. isolates obtained from commercial Egyptian cucumber fields and greenhouses were subjected to the study. When isolate Eg7 of T. harzianum from Egypt was compared with other T. harzianum isolates the level of protection was equal to or greater than the established biological control agents.