Identification des principaux phytopathogènes du poivre (Piper nigrum L.) de Penja et contrôle du dépérissement lent par Trichoderma asperellum et l’extrait hydroéthanolique de Chromoleana odorata

Abstract

Penja pepper production in Cameroon is threatened by pests and diseases. However, little or no information is available on what pests and diseases are responsible nor what effective control measures to implement. Fungicides are used by the majority of farmers as a means of control. The objective of this work was to identify the main bioagressors associated to principals’ diseases of Penja pepper, evaluate the chemicals treatments used by producers and propose the alternatives solutions including plants extracts and antagonists. To achieve the first two objectives, a survey was carried out among 71 producers and field surveys were carried out in 35 pepper plantations located in three study areas (Njombe-Penja, Loum and Tombel). Plant and soil sampling were assessed to identify main diseases and causal agents. Slow decline of pepper and white root rot were identified as major diseases in Penja pepper plantations. They were present in 42% (slow decline) and 51% (white root rot) of the farmers, causing an average of 5% loss per year, which represents a huge loss of income for the producer. DNA sequencing and phylogenetic analysis of the rDNA ITS regions of the isolates identified Armillaria sp. and Phytopythium sp. as potential pathogens of white root rot and slow decline respectively. The third part of the work was devoted to alternative control methods. The fungicides most commonly used by farmers, Trichoderma asperellum, the aqueous and hydroethanolic extracts of three plants (Chromoleana odorata, Phyllantus amarus, Commelina benghalensis) were tested for their control capacity on Phytopythium sp. Both T. asperellum and C. odorata hydroethanolic extract showed good efficacy in reducing the severity of slow decline by 86.1% and 67.2%, respectively. This severity was negatively correlated with chlorophyll a and carotenoid contents in pepper leaves. It is noted that the main diseases were slow decline, white root rot and the potential pathogens are respectively Phytopythium sp. and Armillaria sp. The different control methods tested against Phytopyhium sp. have shown that T. asperellum and C. odorata are promising alternatives to chemical control. Armillaria sp. being more difficult to control requires more specific research and attention.