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Light-regulated asexual reproduction in Paecilomyces fumosoroseus

¹ Departamento de Biotecnología y Bioingeniería, Centro de Investigación y Estudios Avanzados del IPN, Av. Instituto Politécnico Nacional 2308, San Pedro Zacatenco, CP 07360, México DF, Mexico
² Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, AP 70-242, 04510 México DF, Mexico
³ Departamento de Ingeniería Genética de Plantas, Unidad Irapuato, Centro de Investigación y de Estudios Avanzados del IPN, AP 629, 36500 Irapuato Gto., Mexico

Correspondence
Alfredo Herrera-Estrella
aherrera{at}ira.cinvestav.mx

The entomopathogenic fungus Paecilomyces fumosoroseus has been successfully used in the control of several insect pests. Asexually produced spores (conidia) are the means for dispersal and transmission of the entomopathogen; upon contact with the insect cuticle they germinate and penetrate the host. In model fungal systems it has been found that phototropism, resetting of the circadian rhythm, the induction of carotenogenesis and the development of reproductive structures are controlled by blue light. The effect of light quality on conidial yield of P. fumosoroseus was investigated. Incubation in total darkness resulted in continued vegetative growth and lack of reproductive structures. In contrast, growth of the fungus in continuous illumination or under a night–day regime resulted in prolific formation of conidiophores bearing abundant mature conidia. Conidiation was photoinduced in competent mycelia by a single pulse of blue light and colonies were competent only after they had grown at least 72 h under total darkness. The fluence–response curves generated with blue light indicated that the minimal fluence required for the photomorphogenetic response was 180 µmol m^-2 and the half-maximal response was at 400 µmol m^-2. A fluence of 540 µmol m^-2 was enough to saturate the system, inducing the maximum production of 2·12x10⁸ conidia per colony. Higher light intensities markedly decreased conidiation, suggesting the occurrence of a process of adaptation. The authors propose the existence of a dual light-perception system with at least two photoreceptors in P. fumosoroseus, one promoting and one inhibiting conidiation.