Utilization of fungal and bacterial endophytes for the management of the banana nematode Radopholus similis in East African Highland Bananas.

Abstract

East African Highland bananas (EAHB) (Musa spp., AAA-EA) are a staple food to many smallholder farmers in Uganda. Production is constrained by plant parasitic nematodes (PPN) with the burrowing nematode, Radopholus similis being the major PPN. This damages the root system and results into toppling of banana plants especially on rainy days. Management of R. similis is difficult especially in bananas because these nematodes reside inside the roots. Use of biocontrol agents (BCAs) in the management of R. similis in bananas is encouraged however the age of bananas to be enhanced with BCAs and how many times of enhancement with BCAs (inoculation regime) needs to be established. In this study, effect of cultural filtrates of the BCAs against R. similis was tested in vitro as an initial step in testing the BCAs against R. similis. In the screen house, effect of BCAs and their inoculation regimes on R. similis densities in banana plants was also tested. The effect of BCAs on plant growth was tested in the screen house. Five BCAs i.e., three bacteria endophytes; Coccobacillus spp (1DRB1), Bacillus spp (1HRB3) and Bacillus spp (1HRB4) and two fungal endophytes i.e., Trichoderma asperellum (Asperello T34) and Trichoderma asperellum (Real Trichoderma TRC900) were tested against R. similis. Effect of culture filtrates of BCAs on R. similis was determined as percentage paralysis and mortality of nematodes after in-vitro exposure of R. similis to culture filtrates of BCAs in petri dishes. Percentage (%) paralysis was determined after 3, 6 and 12 hours while percentage mortality was determined after 24 hours. All filtrates of fungal and bacterial endophytes paralyzed R. similis. Filtrates of all fungal and bacteria endophytes killed R. similis with 1HRB4 resulting in highest mortality (75.64%). Effect of BCAs, their inoculation regime on R. similis densities was determined as the total number of R. similis extracted from 5g of root at experiment termination. Effect of BCAs and their inoculation regime on growth of plants was determined by measuring height, fresh shoot weight, dry shoot weight, and fresh root weight. There were significant (P < 0.001) effect on reduction of R. similis densities in plants inoculated with fungal and bacterial isolates compared to the control plants that were not inoculated with BCAs. Inoculation regime with biocontrol agents had a significant (P < 0.05) effect on reduction of R. similis densities in banana plants. Biocontrol agents had significant (P < 0.05) effects on increasing plant growth of banana plants. Inoculation regime however had no significant (P > 0.05) effect on increasing plant growth of banana plants. Results from this study indicate that these isolates have the potential to be used as biocontrol agents against R. similis in bananas.