Rice leaf endophytic Microbacterium testaceum: Antifungal actinobacterium confers immunocompetence against rice blast disease

Abstract

Genetic and functional characteristics of rice leaf endophytic actinobacterial member, Microbacterium are described. Morphotyping, multilocus sequence analysis and transmission electron microscopy indicated the species identity of the endophytic bacterium, OsEnb-ALM-D18, as Microbacterium testaceum. The endophytic Microbacterium showed probiotic solubilization of plant nutrients/minerals, produced hydrolytic enzyme/phytohormones, and showed endophytism in rice seedlings. Further, the endophytic colonization by M. testaceum OsEnb-ALM-D18 was confirmed using reporter gene coding for green fluorescence protein. Microbacterium OsEnb-ALM-D18 showed volatilome-mediated antibiosis (95.5% mycelial inhibition) on Magnaporthe oryzae. Chemical profiling of M. testaceum OsEnb-ALM-D18 volatilome revealed the abundance of 9-Octadecenoic acid, Hexadecanoic acid, 4-Methyl-2-pentanol, and 2,5-Dihydro-thiophene. Upon endobacterization of rice seedlings, M. testaceum altered shoot and root phenotype suggestive of activated defense. Over 80.0% blast disease severity reduction was observed on the susceptible rice cultivar Pusa Basmati-1 upon foliar spray with M. testaceum. qPCR-based gene expression analysis showed induction of OsCERK1, OsPAD4, OsNPR1.3, and OsFMO1 suggestive of endophytic immunocompetence against blast disease. Moreover, M. testaceum OsEnb-ALM-D18 conferred immunocompetence, and antifungal antibiosis can be the future integrated blast management strategy.

The endophytic fungal community plays a crucial role in the resistance of host plants to necrotic bacterial pathogens

“…Microbacterium is widely present in plant tissues and is a promising agricultural microbial inoculant that can produce many volatile organic compounds to promote crop growth and has antibiotic effects on pathogens (Barnett et al, 2006; Cordovez et al, 2018). Patel et al (2022) reported that Microbacterium testaceum isolated from rice leaves inhibited the growth of Magnaporthe oryzae by producing volatile compounds such as 9‐octadecenoic acid, hexadecanoic acid, 4‐methyl‐2‐pentanol, and 2,5‐dihydrothiophene. After foliar spraying M. testaceum , the severity of rice blast in the susceptible cultivar decreased by more than 80.0%.…”

Impact of bacterial volatiles on the plant growth attributes and defense mechanism of rice seedling

“…Gram staining and biochemical properties were used to characterize isolated endophytic isolates [ 12 , 13 ].The plant growth promoting biochemical properties of isolated rice plant endophytes were explored by investigating the indole-3-acetic acid (IAA) [ 14 ], NH 3 (ammonia) production [ 15 ], phosphate solubilization [ 16 , 17 ], siderophore production [ 18 ], zinc solubilization [ 19 ], Silicate solubilization [ 20 , 21 ], Potassium solubilization [ 22 ], and antagonistic effect of BVCs were observed against the plant pathogen Magnaporthe oryzae [ 23 , 24 ].…”

An updated view of bacterial endophytes as antimicrobial agents against plant and human pathogens

“… Wheat Biocontrol agent, antagonistic activity, plant growth promotion, Tao et al, 2014 ; Tian et al, 2017 Microbacterium sp. Coptis teeta, Rice, Halimione portulacoides Biocontrol agent of blast disease, production of phytohormones or enzymes, plant growth promotion Liu et al, 2020 ; Patel et al, 2022 Gordonea terrae Avicena marina, barley, rice Produce surface-active compounds and pigments like carotenoids that allow survival under different conditions and stress, plant growth promotion Sowani et al, 2018 ; Soldan et al, 2019 ; Burkholderia phytofirmans Grapevine, Switchgrass, Arabidopsis thaliana, White lupin, and maize Growth promotion, promotes plant tolerance to biotic and abiotic stressors Compant et al, 2008 ; Kim et al, 2012 ; Zuniga et al, 2013 ; Kost et al, 2014 Enterobacter sp. Hybrid poplar Growth promotion, hinders the activity of soil-borne pathogens, biofertilizer Doty et al, 2017 ; Ludueña et al, 2019 Gluconacetobacter diazotrophicus Sugarcane, rice, wheat, and sorghum Promote plant growth in drought stress and low nitrogen conditions by fixing nitrogen, create indoleacetic acid to aid in the growth of plants.…”