Expression of Putative Defense Responses in Cannabis Primed by Pseudomonas and/or Bacillus Strains and Infected by Botrytis cinerea

Abstract

Cannabis (Cannabis sativa L.) offers many industrial, agricultural, and medicinal applications, but is commonly threatened by the gray mold disease caused by the fungus Botrytis cinerea. With few effective control measures currently available, the use of beneficial rhizobacteria represents a promising biocontrol avenue for cannabis. To counter disease development, plants rely on a complex network of inducible defense pathways, allowing them to respond locally and systemically to pathogens attacks. In this study, we present the first attempt to control gray mold in cannabis using beneficial rhizobacteria, and the first investigation of cannabis defense responses at the molecular level. Four promising Pseudomonas (LBUM223 and WCS417r) and Bacillus strains (LBUM279 and LBUM979) were applied as single or combined root treatments to cannabis seedlings, which were subsequently infected by B. cinerea. Symptoms were recorded and the expression of eight putative defense genes was monitored in leaves by reverse transcription quantitative polymerase chain reaction. The rhizobacteria did not significantly control gray mold and all infected leaves were necrotic after a week, regardless of the treatment. Similarly, no systemic activation of putative cannabis defense genes was reported, neither triggered by the pathogen nor by the rhizobacteria. However, this work identified five putative defense genes (ERF1, HEL, PAL, PR1, and PR2) that were strongly and sustainably induced locally at B. cinerea’s infection sites, as well as two stably expressed reference genes (TIP41 and APT1) in cannabis. These markers will be useful in future researches exploring cannabis defense pathways.

The bud rot pathogens infecting cannabis (Cannabis sativa L., marijuana) inflorescences: symptomology, species identification, pathogenicity and biological control

“…The establishment of bud rot pathogens such as B. cinerea can be reduced by pre-emptive colonization of the inflorescence with biological control agents, which are able to establish in sufficient numbers on the inflorescences. Future research aimed at understanding the biochemical basis for susceptibility of the inflorescence to pathogens, as well as the concomitant changes in host gene expression (Balthazar et al 2020) and associated changes in the composition of the microbiome (Busby et al 2017), should provide useful avenues towards the management of these destructive bud pathogens.…”

Diseases of Cannabis sativa Caused by Diverse Fusarium Species

“…In C. sativa, treatment with PGPR reduced incidence of diseases caused by pathogenic fungi. Five putative defense genes were "strongly and sustainably induced locally" in C. sativa at the infection sites of Botrytis cinerea (Balthazar et al, 2020). Many growers add mycorrhizal inoculum to C. sativa production systems to increase plant quality, but there are no reports on using these microorganisms alone or in combination with other microbial pesticides for control of disease.…”

Exploiting Beneficial Pseudomonas spp. for Cannabis Production

“…Pioneering assays of microbial inoculants in cannabis, using P. putida, P. protegens, Pseudomonas synxantha and Pseudomonas simiae among other PGPR microorganisms, have already successfully increased several indicators of biomass and fiber yield, such as total plant weight and/or stem length, diameter, and weight (Jin et al, 2014;Conant et al, 2017;Pagnani et al, 2018;Balthazar et al, 2020;Comeau et al, 2021;Kakabouki et al, 2021a,b). Further studies are needed to assess the full agronomic potentials of this promising avenue with indicators considering fiber quality, such as internode length and bast fiber content (Jin et al, 2014), fiber width (Müssig and Amaducci, 2018), pectin and lignin content reduction and fiber decortication efficiency (Petit et al, 2020).…”

“…Conversely, a recent study concluded that drenching the soil with P. synxantha, P. simiae and/or Bacillus spp. rhizobacteria did not protect hemp against Botrytis foliar infection and failed to trigger defenserelated gene expression in hemp leaves (Balthazar et al, 2020). This unsuccessful attempt was tentatively attributed to a lack of production of ISR-inducing compounds by the bacteria, or to the inability of hemp to perceive such compounds in the rhizosphere (Beneduzi et al, 2012).…”