Endophytic effects of Aspergillus oryzae on radish (Raphanus sativus) and its herbivore, Plutella xylostella.

Abstract

We provide evidence that Aspergillus oryzae not only acts as an endophyte in Raphanus sativus, but also works as a plant growth promoter and provides some protection against its herbivore, Plutella xylostella affecting its feeding rate, mortality and fitness parameters, thereby contributing to the pest population suppression. Seed inoculation of radish seeds with the fungus Aspergillus oryzae allowed its establishment as an endophyte promoting plant growth and negatively affecting fitness parameters of its major herbivore, diamondback moth, Plutella xylostella. Endophytic fungi may contribute to the growth of their host plants and enhance resistance to herbivores and diseases. We evaluated the effect of A. oryzae (Ahlburg) E. Cohn as an endophyte in radish (Raphanus sativus L.) on growth and development of the plants themselves and their major herbivore, the diamondback moth P. xylostella (L). A. oryzae colonization rates in leaves were significantly higher than in roots and stems, with a rate of 80% in leaves, 40% in stems and 20% in roots 1week after seed inoculation. Colonization gradually decreased in the various plant tissues, and disappeared completely in roots, stems and leaves within 2, 5 and 7weeks, respectively. A. oryzae did not affect seed germination; however, it promoted radish growth with endophytic plants attaining average heights of 116mm compared to 99.6mm in the controls at the third week post-inoculation. The P. xylostella fitness parameters, consumption, larval and pupal weights, and feeding on the endophytic plants were significantly lower than the controls, while larval mortality was significantly higher. Larvae fed on endophytic plants consumed 0.46mg less leaf matter in the first week post seed inoculation and weighed 0.83mg less as mature 4th instars than controls. We have demonstrated that A. oryzae can establish as an endophyte in R. sativus through seed inoculation providing some plant growth promotion and protection against its herbivore by increasing its mortality and negatively affecting its fitness parameters, suggesting that adopting seed treatments with A. oryzae may be beneficial in the commercial cultivation of radish.