Chapter 1 - Rhizopus stolonifer (Soft Rot)

Abstract

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 3.6kJm2 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.