Induction of systemic resistance by mixtures of antagonist bacteria for the management of crown rot complex on banana

Abstract

Among nine native bacterial strains isolated from banana fruit surface and rhizosphere and six bacterial strains introduced from the culture collection, three native strains viz., non-fluorescent Pseudomonas (NFP 6 ), Pseudomonas fluorescens (Pf3a), and Bacillus subtilis (BS 1 ); and two bacterial strains from culture collection viz., Azospirillum (AS1) and Azotobacter (AZ1) have recorded maximum inhibition of mycelial growth of crown rot pathogens (Lasiodiplodia theobromae and Colletotrichum musae) under in vitro condition. When these effective bacterial strains were treated on banana fruits under in vivo, significant reduction of crown rot disease and increased shelf life of banana was observed. However, bacterial strains applied as three way combinations (NFP 6 ? Pf3a ? BS 1 ) had greater effect compared with individual and two way combination of bacterial antagonist treatments. The effect of crown rot disease reduction was also comparable to that of fungicide Benomyl (0.1%) both under cold and room temperature storage conditions. Besides, the induction of defense-related enzymes such as phenylalanine ammonia-lyase (PAL), peroxidase (PO), polyphenoloxidase (PPO), and the accumulation of phenolics in banana fruit due to the application of bacterial antagonists were also studied at five different time intervals viz. 0th, 1st, 3rd, 5th and 7th days after treatment. When banana fruits treated with bacterial antagonists (individually and also in different combinations) and challengeinoculated with crown rot pathogens, up to fourfold increase in defense-related enzymes and 3.6 fold increase in phenolic content was observed compared with control. The activity of these defense-related enzymes and phenolic content had gradually increased from 1st day after treatment to 3rd after treatment and reached their peak on 5th day after treatment. Among the bacterial antagonists which have been applied individually and in different combinations, the banana fruits treated with three-way antagonist mixture, i.e., NFP 6 ? Pf3a ? BS 1 recorded maximum induction of defense-related enzymes and accumulation of phenolics compared with individual and two-way combination of antagonist mixtures. This study suggest that the increased induction of defense-related enzymes and phenolic content due to the treatment of banana fruits with bacterial antagonists might have involved in the reduction of crown rot severity and in turn increased the shelf life of banana fruits.

Plant growth promoting rhizobacteria (PGPR) induces resistance against Fusarium wilt and improves lycopene content and texture in tomato

“…Similarly, mango trees sprayed with P. fluorescens FP7 recorded a greater amount of the enzymes against Colletotrichum gloeosporioides infection ( Vivekanadan et al, 2004). Mixture of Pseudomonas (NFP6), P. fluorescens (Pf3a), and B. subtilis (BS1) was found to induce defence reaction in banana against crown rot caused by Lasiodiplodia theobromae and Colletotrichum musae under in vivo conditions (Sangeetha et al, 2010). Phenolics are known to have fungitoxic effect and a role in strengthening the host cell wall.…”

“…The PGPR are known to act as biocontrol agents through competition for ecological niche/substrate and production of siderophores, antibiotics, hydrogen cyanide and fungal cell wall lysing enzymes (Glick and Bashan 1997;Wang et al, 2000;Saravanakumar et al, 2007). PGPR are also involved in induced systemic resistance (ISR) against many diseases in a wide range of crops (Kloepper and Beauchamp, 1992;Liu et al, 1995;Chen et al, 2000;Sangeetha et al, 2010). Although the application of PGPR and their effects on disease or pest control and yield have been well established for a wide range of crops, information on fruit quality in terms of lycopene content and texture is very limited.…”

Utilization of chitinolytic bacterial isolates to control anthracnose of cocoa leaf caused by Colletotrichum gloeosporioides

“…Recently, the use of naturally occurring bacteria (Sangeetha et al, 2010;Akinbode and Ikotun, 2008;Mahadtanapuk et al, 2007) and antagonistic fungi (Adekunle and Ogbebor, 2009;Akinbode and Ikotun, 2008;Shovan et al, 2008) for biocontrol of Colletotrichum spp. has been recognized.…”

“…The lytic activity of bacteria is one of a number of mechanisms that has been implicated in biocontrol (Alabouvette et al, 2006). Recently, the use of naturally occurring bacteria (Sangeetha et al, 2010;Akinbode and Ikotun, 2008;Mahadtanapuk et al, 2007) and antagonistic fungi (Adekunle and Ogbebor, 2009;Akinbode and Ikotun, 2008;Shovan et al, 2008) for biocontrol of Colletotrichum spp. has been proposed.…”

Bacterial antagonists and hexanal-induced systemic resistance of mango fruits against Lasiodiplodia theobromae causing stem-end rot

“…Combined application of two or more biocontrol agents with preferred substrates, which in turned out to be more efficient than either of them alone (Narayanan et al 2016). Therefore, use of compatible bacterial antagonist as consortia would emphasize more effective against postharvest diseases (Sangeetha et al 2010). Induction of defense enzymes has been reported against several postharvest pathogens by bioinoculants (Peeran et al 2014;Wang et al 2014;Guo et al 2015).…”