The control of plant diseases by chemotherapy

Successful chemotherapy is obtained at present with the antibiotics, such as streptomycin, for certain bacterial and virus diseases of plants. Promising results have been obtained with chemotherapeutic chemicals other than the antibiotics in the control of plant diseases caused by species of such fungi as Botrytis, Fusarium, and Phytophthora.     

Modulation of plant resistance to diseases by water-soluble chitosan

Low-molecular-weight water-soluble chitosan with a molecular weight of 5 kDa obtained after enzymatic hydrolysis of native crab chitosan was shown to display an elicitor activity by inducing the local and systemic resistance of Solanumi tuberosum potato and Lycopesicon esculentum tomato to Phytophthora infestans and nematodes, respectively. Chitosan induced the accumulation of phytoalexins in tissues of host plants, decreased the total content and changed the composition of free sterols producing adverse effects on infesters, activated chitinases, beta-glucanases, and lipoxygenases, and stimulated the generation of reactive oxygen species. The activation of protective mechanisms in plant tissues inhibited the growth of taxonomically different pathogens (parasitic fungus Phytophthora infestans and root knot nematode Meloidogyne incognita).     

Scanning electron-microscopy of abscission-zone surfaces of Valencia-orange fruit

Summary The scanning electron-microscope was used to obtain a more adequate view of the separation surfaces exposed when the stem was pulled from the fruit of Valencia orange. Separations were made at 0, 24 and 48 h after ethylene treatment of the fruit. The most noticeable differences are the lessened amount of tearing in proximal vascular bundles at 48 h and decreased rupture of distal parenchyma cells first observed at 24 h.     

Broad spectrum management of plant diseases by phylloplane microfungal metabolites

Plant surfaces are colonised by an array of microbes. These microbes have been implicated in protecting plants against invading pathogens. Studies have demonstrated that metabolites of phylloplane microfungi can induce defence responses in their host plants. This investigation relates to formulation of a biocide from metabolites of Aspergillus niger, Trichoderma viride, Alternaria alternata and Chaetomium globossum, which are common phylloplane colonisers of tropical plants. The biocide was found to reduce disease incidence through induction of alterations in defence physiology of crop plants.     

Diagnosis of viruses infecting essential-oil plant crops by using immunoenzyme analysis

The use of the EIA point technique permitted the detection of viruses affecting essential-oil plants. The method is simple, highly specific, sensitive and can be used for checking seedlings prior to planting.     

Biological control of fungal plant diseases

Research has demonstrated the agricultural potential of biological control. For airborne pathogens as well as for soilborne pathogens similar strategies based on different targets in the life cycle of the pathogen can be distinguished, viz. (1) microbial protection of the host against infection, (2) microbial reduction of pathogen sporulation and (3) microbial interference with pathogen survival. Some successes and failures with respect to these targets will be discussed and include (1) biocontrol of seedling diseases, root pathogens, and post-harvest diseases (2) biocontrol of powdery mildew and Botrytis cinerea (3) biocontrol of sclerotial pathogens. Despite of a lot of research on biological control of plant diseases, the number of products available is limited and their market size is marginal. The market for biological control products is not only determined by agricultural aspects such as the number of diseases controlled by one biocontrol product in different crops but also by economic aspects as cost-effective mass production, easy registration and the availability of competing means of control including fungicides. The future development of low-chemical input sustainable agriculture and organic farming will determine the eventual role of biological control in agriculture.