Rice recycling: a simple strategy to improve conidia production in solid-state cultures.

A Cando‐Narvaez,O Loera,J.E Méndez‐Hernández

doi:10.1111/lam.13614

Abstract

Here we studied at a laboratory scale a potential strategy to revalorize the residual rice remaining at the end of a conventional conidia production process in solid-state culture. The conidia production of Trichoderma asperellum Th-T4 (3) and Metarhizium robertsii Xoch-8.1 started with the use of fresh rice (unrecycled rice) as the substrate (cycle one), and continued with the use of recycled rice in successive cycles of conidia production. The rice remaining at the end of the first cycle was reused without any further sterilization or reinoculation. As a result, it was observed that the conidia production and productivity significantly increased in both fungi. Conidia production in T. asperellum Th-T4 (3) increased from 1 × 109 (first cycle) to 2·9 × 109 conidia per gram of initial dry substrate (con⋅gds-1 ) (second cycle using recycled rice), while in M. robertsii Xoch-8.1, this parameter increased form 5·7 × 108 to 1·4 × 109 con⋅gds-1 . Both fungi grew faster and conidiated earlier when recycled rice was used as the substrate, therefore, conidia productivity was also significantly improved. Furthermore, the use of recycled rice did not affect conidia viability. This is the first report about a recycling methodology completely free of extra-processing steps, and useful to increase conidia production and productivity.

Highlights

The economic losses caused by pests can be as high as 40 % of the total annual yield worldwide, which has led to an excessive dependence on chemical pesticides [1]
Conidia production in T. asperellum Th-Th4 (3) increased from 1.0×109 to 4.9×109 con/gds, while in M. robertsii Xoch-8.1, this parameter increased form 5.7×108 to 3.8×109 con/gds. This strategy did not affect the viability of the conidia produced using recycled rice relative to the conidia produced using fresh substrate
Fungal mycelia quickly covered the rice grains and a uniform conidia layer was observed 3 days after inoculation (Fig. 1b). This point was considered the end of cycle 1, and the incubation was shortly interrupted in order to achieve the harvesting and counting of the conidia

Summary

Introduction

The economic losses caused by pests can be as high as 40 % of the total annual yield worldwide, which has led to an excessive dependence on chemical pesticides [1]. The most widely used fungal biopesticides are made from infectious propagules of the genera Beauveria, Metarhizium, and Trichoderma [3, 4]. The production of these biopesticides can be carried out by submerged fermentation (SmF) or solid-state cultures (SSC) [5]. At the end of a conidia production cycle, around 80 % of the initial substrate that was added remains unused [7]. The reuse of this substrate has been proposed in previous works [8, 9, 10]; the suggested methodologies comprise extra drying, washing, and sterilization steps, which increase the cost of the process

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Conclusion