PHYTOPATHOGENIC FUNGI IN RICE (Oryza sativa) AND THEIR ASSOCIATION WITH Steneotarsonemus spinki (ACARI: TARSONEMIDAE) IN TABASCO, MEXICO.

Abstract

In the tropical regions of the Americas, damages to rice (Oryza sativa) —such as sheath and grain blight, and unfilled spikelets (vaneo)— have been described; they are attributed to the combined effect of the fungus Sarocladium oryzae and the mite Steneotarsonemus spinki. In Mexico, this mite was first detected in 2006, and since then it is reported in the states of Campeche, Tabasco, and Veracruz; however, in those states, the presence of S. oryzae or its association with the mite, is not confirmed. The objective of this study was to identify the fungi that infect rice in three locations in the state of Tabasco. The hypothesis was that the association between S. spinki and S. oryzae results in grain blight and unfilled spikelets. From July 2014 to July 2015, samples were taken from three rice plantations in the municipalities of Cárdenas, Huimanguillo, and Comalcalco, Tabasco, in order to identify the phytopathogenic fungi present in the sites and determine if there is a mite-fungus association that causes unfilled spikelets. In each sampling date 50 plants from each plot were randomly selected at each sampling site. Pyricularia oryzae, Helminthosporium oryzae, Verticillium sp., and Fusarium sp. were identified, S. oryzae was not detected and S. spinki had a maximum incidence of 90% in the rice plants in Cárdenas and Huimanguillo. No trace of S. spinki was found in Comalcalco, but H. oryzae and Verticillium sp. were indeed found in the area —their incidence was less than 1% in the three municipalities. Although unfilled spikelets and sheath and spike blight were observed, the low incidence of phytopathogenic fungi suggests that their association with S. spinki is minimal or non-existent; therefore, unfilled spikelets are caused by the mite and not by its infestation combined with some of the fungi identified.