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Worldwide, papaya is a highly consumed fruit; however, they are very susceptible to the attack of the fungus Colletotrichum gloeosporioides. The fungal cell wall has mostly chitin, which is degraded by the chitinases enzymes that are synthesized as part of the plant's defence system. For diagnose a fungal disease, it is necessary to find a biological indicator as well-referred to as biomarkers which in turn could be detected through biosensors. Until now, there was no information about the activity of the chitinases in inoculated and stored papaya, at different phenological stages (preharvest stage) of the fruit and during storage (postharvest stage). The results showed higher activity of the enzyme in those stages close to the harvest period (c.a. 42 and 113 IU mg−1 protein) and lower activity (0 IU mg−1 protein) at the senescence stage during postharvest; meanwhile, in papayas artificially inoculated with C. gloeosporioides, at both the pre and postharvest stages, the chitinolytic activity increased, although, decreased as storage days progressed. Based on these results, chitinase activity in papaya could act as an indicator of the fungal growth for further use in the design of a biosensor for the detection of this fungus.

Summary Environmental and technological influences complicate the task of achieving disease-free products in the ornamental industry. Research is needed to support progress in the development of integrated environmental, biological, and chemical control techniques for management of diseases in floriculture. However, due to the unavailability of desirable resistance in cultivars and exorbitant cost of chemicals for the management of diseases in ornamentals, the introduction of biological and alternatives methods is believed to be an alternative to chemical methods. Moreover, management practices using a single control measure are not successful in controlling the diseases. For this reason, integrated management practices based on resistant cultivars, chemical methods, biological methods, and alternatives under experimentation (chitosan, extracts, and essential oils) are being adopted for successful management of diseases in ornamentals.

Summary A number of studies have confirmed the in vitro fungicidal effect of chitosan on various phytopathogenic fungal families including among others, Mucoraceae, Pleosporaceae, and Glomerellaceae. Investigations of the morphology and ultrastructure of the chitosan-treated fungi in in vitro studies and during the plant-pathogen interaction of various pathosystems have been carried out by using conventional optical/light microscopy and with other advanced instruments including SEM, TEM, and confocal microscopy. The electrostatic interaction between chitosan and the microorganism is noted by dramatic alterations observed from the damaged structure of the cell wall and plasma membrane. The integrity of organelles including vacuoles was seriously affected, leading in some cases to lysis of the fungal cell. During the host-pathogen interaction, formation of structural barriers by the host, mainly through inter- and intracellular synthesis of phenolic-lignin-like material that stops fungal invasion, was also observed. Fungal growth was not beyond the outer cortical area of the infected tissues, while damage on fungi was similar to those observed in in vitro studies. Microscopic examinations have confirmed the fungicidal and eliciting properties of chitosan.

Summary In this chapter, the major rice diseases and their control methods are described. Results based on the direct action of chitosan against the main pathogenic fungi and bacteria of this crop are presented and discussed. The induction of defense mechanisms of rice mediated by chitosan and their role in plant protection from diseases under both controlled and field conditions are mentioned. Evidence shows that rice protection mediated by chitosan is achieved by a direct action of this biopolymer on the pathogen, and also indirectly by induced resistance. Therefore, enough data prove the feasibility of using chitosan to protect rice against diseases, with advantages over chemical fungicide application.

Rhizopus stolonifer is considered the most important species in the genus Rhizopus . Disease symptoms that characterize R. stolonifer infection are watery areas quickly covered by coarse, gray hairy mycelia forming a mass of black sporangia at their tips. Infection usually occurs during harvest and handling. Due to the wide array of hosts that R. stolonifer can infect and its fast penetration and colonization, it has become an important target to control. Overall, R. stolonifer is controlled using synthetic fungicides; among the various registered fungicides are thiabendazole, benomyl, imazalil, propiconazole and thiocarbamates. The fungicides fluodioxonyl, tebuconazole, fenhexamide and azoxystrobin have also achieved notable control of this fungus. Sanitizers like chlorine, sodium hypochlorite, calcium hypochlorite, ozone and peracetic acid have shown to have good control on Rhizopus . Of the various non-conventional methods under experimentation, antagonists have attracted considerable attention. Bacteria including Pantoe agglomerans , Enterobacter cloacae , Pseudomonas syringae , and Bacillus spp., as well as yeasts of the genera Pichia , Kloeckera , Candida , Cryptoccoccus , Metschnikowia and Acremonium , have exerted a significant control on this fungus. Aqueous plant extracts belonging to the botanical families Amaryllidaceae, Annonaceae, Arecaceae, Bromeliaceae, Caricaceae, Lamiaceae, Lauraceae, Leguminosae, Meliacea, Myrtaceae, Pinaceae, Sapotaceae, Solanaceae and Urticaceae, along with the essential oils of the genera Thymus , Cinnamom , Origanum and Citrus , have also produced excellent results under experimentation. UVC irradiation levels of up to 3.6 kJm 2 showed levels of control up to 50% on R. stolonifer . Chitosan, a widely known chitin derivative, alone or in combination with other natural products, has been able to reduce significantly Rhizopus soft rot on various horticultural commodities at various concentrations. Volatiles, hypobaric atmospheres, salts, minerals, plant phenolics, hot water, wax and salicylic acid have resulted in good control methods with promising applications.