Metarhizium Associated with Coffee Seedling Roots: Positive Effects on Plant Growth and Protection against Leucoptera coffeella

Metarhizium species can be mutualistic symbionts of plants. They are able to colonize roots, promote plant growth and provide protection against pests. We previously found Metarhizium robertsii and M. brunneum associated with coffee roots in a diversified coffee system. Here, we investigated whether these fungi, when inoculated in coffee seedlings, can associate with roots, improve seedling growth and indirectly protect against the coffee leaf miner (CLM) Leucoptera coffeella (Lepidoptera: Lyonetiidae). We performed a greenhouse experiment with coffee seedlings using suspensions of each Metarhizium species applied as soil drenches to potted seedlings. We also challenged these plants with CLM infestation (two adult couples per plant). We recovered Metarhizium spp. from most of the seedling roots 43 days after fungal inoculation. Plants inoculated with M. robertsii showed a 30% leaf area increase compared to the control. Both isolates promoted protection against CLM in coffee seedlings, reducing the percentual of leaf area mined and prolonging CLM development time by two days versus controls. Besides this protection provided by Metarhizium, M. robertsii also improves seedling growth. Therefore, these Metarhizium species could be considered for the development of inoculants for coffee seedlings.