Less Virulent Leptosphaeria biglobosa Immunizes the Canola Plant to Resist Highly Virulent L. maculans, the Blackleg Pathogen

Abstract

Leptosphaeria biglobosa is a less virulent Leptosphaeria spp. that causes blackleg disease in canola. Previous studies from our lab have shown that inoculation with the less virulent L. biglobosa can boost the resistance of canola plants against the highly virulent L. maculans. The objective of this study was to confirm the effectiveness of L. biglobosa as a biocontrol agent against L. maculans utilizing morphology, fluorescence microscopy, gene quantification, and transcriptomic analysis. The in planta development of two Leptosphaeria species inoculated at different time points was assessed using fluorescent protein-tagged isolates which are GFP-tagged L. maculans and DsRed-tagged L. biglobosa. The growth inhibition of L. maculans by pre-and co-inoculated L. biglobosa was supported by no lesion development on cotyledons and no or weak fluorescence protein-tagged mycelia under the confocal microscope. The host defense-related genes, WRKY33, PR1, APX6, and CHI, were upregulated in L. biglobosa inoculated Westar cotyledons compared to L. maculans inoculated cotyledons. The quantification of each pathogen through qPCR assay and gene expressions analysis on host defense-related genes by RT-qPCR confirmed the potential of L. biglobosa “brassicae’ in the management of the blackleg disease pathogen, L. maculans ‘brassicae’, in canola.

Co‐inoculation timing affects the interspecific interactions between phoma stem canker pathogens Leptosphaeria maculans and Leptosphaeria biglobosa

“…Although both Leptosphaeria species were characterised to have hemi-biotrophic lifestyles, differences between these two pathogens in terms of nutritional strategies were reported, with some even referring to L. biglobosa as a 'necrotroph'. 38,39 Additionally, one of the recent investigations of differences in metabolic capacity between Leptosphaeria species reported L. biglobosa to be less specialised, with L. maculans coevolving more strictly with the plant host. 36 Therefore, one of the hypotheses to explain the mechanisms of these interactions is that L. biglobosa utilised the resources more efficiently and potentially caused competitive exclusion of L. maculans by employing a resource-mediated (exploitative) competition strategy.…”

“…Therefore, the differences in metabolic capacity between L. maculans and L. biglobosa may have been due to differences in their nutritional strategies. Although both Leptosphaeria species were characterised to have hemi‐biotrophic lifestyles, differences between these two pathogens in terms of nutritional strategies were reported, with some even referring to L. biglobosa as a ‘necrotroph’ 38,39 . Additionally, one of the recent investigations of differences in metabolic capacity between Leptosphaeria species reported L. biglobosa to be less specialised, with L. maculans co‐evolving more strictly with the plant host 36 .…”

Studying temperature's impact on Brassica napus resistance in order to identify key regulatory mechanisms using comparative metabolomics

“…According to the results obtained in the study of Canola-LM interaction, the elevated temperature might negatively affect the resistance of the R cultivar to LM. The capacity of many pathogens to tolerate and adapt rapidly to circumstances beyond the optimum growth temperature of their host plants may account for the large numbers of adversely affected resistances seen at increased temperatures 24 . Under high-temperature growth conditions, the resistant genotypes of B. napus achieve a state of homeostasis, wherein both the activation and suppression of defensive mechanisms take place.…”

“…With the aim of improvement of our knowledge of the physiology of plant-fungus interactions challenged with high temperature, the canola cultivars, Excel (carrying Rlm7 and QTL, resistant) and Drakkar (without any resistance gene and QTL, susceptible) were infected with ME24 isolate and studied under optimum temperatures (21/16ºC) and elevated temperatures (28/23ºC) at different time intervals after infection. The Rlm7 gene in B. napus is a valuable source of resistance for controlling blackleg disease on oilseed rape 22,23,24 . The effectiveness of the Rlm7 gene for control of LM disease epidemics was more durable than other resistance genes against LM because Rlm7 has been used commercially for more than 15 years; for the time being, this resistance gene is useful in preventing phoma stem canker 22 .…”

Effective control of Leptosphaeria maculans increases importance of L. biglobosa as a cause of phoma stem canker epidemics on oilseed rape

“…However, it has been difficult to distinguish ascospores of L. maculans and L. biglobosa in air samples by visual methods; the timing and abundance of L. maculans and L. biglobosa ascospores released in the air can only be distinguished by speciesspecific qPCR. 12,20,31 Additionally, there is evidence that preinfection by one of the Leptosphaeria species confers increased resistance to the other species, 39,40 which is likely to affect subsequent proportions of the two species in inoculum produced in a local population. This work aims to investigate the contribution of L. biglobosa to phoma stem canker epidemics by distinguishing (i) phoma stem canker caused by L. maculans and L. biglobosa on oilseed rape cultivars with different levels of resistance, and (ii) seasonal differences between L. maculans and L. biglobosa in the timing and abundance of release of ascospores.…”