Isolation of indole-producing endophytes from mangrove species: growth promoter of Musa acuminate (Lacatan) and biological control agent against Ralstonia solanacearum.

Abstract

Fungal endophytes were isolated from leaves, stems and roots of mangrove plants to investigate its ability to promote growth of Musa acuminata and as biological control agent against Ralstonia solanacearum. The isolates were subjected to IAA-test using Salkoswski’s reagent and agar plug assay. IAA-producing isolates formed red halo with different intensities that is directly proportional to the concentration of IAA produced. Zones of inhibition formed around the agar plugs show that the isolates inhibited the growth of R. solanacearum. M. acuminata plantlets were then infected with the following IAA-forming endophytes to assess the potential of each to promote shoot growth (treatment 1, isolate from leaves Bruguiera sexangula which produced the highest level of IAA, treatment 2, isolate from the roots of Pemphis acidula and treatment 3, isolates from a mixture of both). The height of M. acuminata plantlets were observed every two weeks. Results showed that both treatments 2 and 3 promoted growth of M. acuminata while treatment 1 inhibited increase in shoot length. The latter is due to the high concentration of IAA produced by the isolate that is inhibitory for plant growth. Two isolates showed antimicrobial activity against R. solanacearum. Statistical analysis showed that the The effect of the two isolates against R. solanacearum is the same.