Soto Esguerra, Roberto C.

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    Evaluación de tratamientos para el control de hongos asociados a la yautía (Xanthosoma spp. Schott) selección Nazareno y el mal seco bajo condiciones de invernadero y laboratorio
    (2017) Soto Esguerra, Roberto C.; Zapata Serrano, Mildred; College of Agricultural Sciences; Bosques Vega, Ángel; González Vélez, Agenol; Department of Crops and Agro-Environmental Sciences; Colón Ramírez, Silvestre
    The tanier (Xanthosoma spp.) is an edible aroid of nutritional value and of economic importance for many tropical countries. During the past thirty years, the production of tanier in Puerto Rico has decreased by more than 90%. The main factor has been the disease locally known as "mal seco", which causes root rot, reduced yield and death of plants. The purpose of this research was to evaluate different treatments for the control of the fungi associated with the root rot disease on tanier under greenhouse and in vitro conditions. In Phase 1, biological products and a fungicide-bactericide were tested in ‘Nazareno’ in soil managed in two different ways under greenhouse conditions: (1) fallow soil (FAS), without sowing tanier for three years, and (2) soil of continuous use (SC), previously planted with tanier. Eight treatments (Ts) were tested in a randomized complete block design for each soil. No statistical differences between Ts were found. FAS had higher corms and root weights and a lower root damage percentage compared to SC. In Phase 2, fungi were isolated from soil and roots samples obtained from the two soil types. Thirty different fungi strains were identified. Fusarium solani was the only pathogen associated with the root rot disease found in the greenhouse samples and the most frequent in the population. The 30 strains of fungi were evaluated in pathogenicity tests (PT) at greenhouse and in vitro conditions. F. solani, Pythium spp., Rhizoctonia solani and Sclerotium rolfsii were included in the trials. In the greenhouse's PT the only fungi causing significant damage to the buds and inhibiting root development was S. rolfsii. Corm discs were used to determine the virulence of the fungi under in vitro conditions. The most virulent fungi were: Aspergillus niger, F. solani strain 1, F. solani strain 2 and S. rolfsii. In Phase 3, Ts for the control of the pathogenic fungi found in the in vitro PT were evaluated. Trichoderma harzianum and Scolecobasidium spp. were selected as potential biocontrol fungi of the patogens associated with the root rot disease. Two in vitro control experiments were performed: on potato dextrose agar (PDA) and on corm discs. Fungi used were R. solani (Rs), Pythium spp. (Py), F. solani 1 (Fs 1), F. solani 2 (Fs 2) and A. niger (An). Commercial Ts used were CuOH (Kocide 3000®), Serenade® and Bioplex® and the non-commercial ones were the fungi T. harzianum (Thar) and Scolecobasidium spp. (Scol). In the PDA tests, the pathogen growth and the area of inhibition caused by the Ts were measured for seven days in two factorial design assays: one with commercial Ts (6 x 4) and one with non-commercial Ts (6 x 3). CuOH didn’t inhibit the growth of pathogenic fungi with results equal to the Control. Serenade® was better than Bioplex® inhibiting Fs 1, Py and Sr, whereas Bioplex® was better inhibiting Fs 2 and Rs, although not significantly. Thar was able to inhibit the growth of Sr and the other pathogens much more than Scol. In the second experiment, corm discs were inoculated in two different modes and times: pre-treatment (inoculation with the pathogen after the tissue was submerged in the T), and post-treatment (inoculation with the pathogen before the tissue was sprayed with the T). In the pre-treatment trial, CuOH was better in the control of Rs, Scol and Thar were better in the control of An, and Thar in the control of Sr. In the post-treatment trial, Serenade® and Scol were the best Ts. In the simple effects, Scol was better at the control of Sr, Serenade® was better at the control of Fs 1, Fs 2 and Rs, and CuOH at the control of An. The evaluated Ts have potential to give protection to the tanier seed at field level.