Limits...
Interactions between cauliflower and Rhizoctonia anastomosis groups with different levels of aggressiveness.

Pannecoucque J, Höfte M - BMC Plant Biol. (2009)

Bottom Line: We demonstrated the pronounced deposition of phenolic compounds and callose against weak and non-aggressive AGs which resulted in a delay or complete block of the host colonization.Degradation of pectic compounds was observed for all pathogenic AGs, except for AG 2-2 IIIb.Ranking the AGs based on infection rate, level of induced host responses and pectin degradation revealed a strong correlation with the disease severity caused by the AGs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Phytopathology, Faculty of Bioscience Engineering, Ghent University, Coupure Links, 653, B-9000 Gent, Belgium. joke.pannecoucque@ugent.be

ABSTRACT

Background: The soil borne fungus Rhizoctonia is one of the most important plant pathogenic fungi, with a wide host range and worldwide distribution. In cauliflower (Brassica oleracea var. botrytis), several anastomosis groups (AGs) including both multinucleate R. solani and binucleate Rhizoctonia species have been identified showing different levels of aggressiveness. The infection and colonization process of Rhizoctonia during pathogenic interactions is well described. In contrast, insights into processes during interactions with weak aggressive or non-pathogenic isolates are limited. In this study the interaction of cauliflower with seven R. solani AGs and one binucleate Rhizoctonia AG differing in aggressiveness, was compared. Using microscopic and histopathological techniques, the early steps of the infection process, the colonization process and several host responses were studied.

Results: For aggressive Rhizoctonia AGs (R. solani AG 1-1B, AG 1-1C, AG 2-1, AG 2-2 IIIb and AG 4 HGII), a higher developmental rate was detected for several steps of the infection process, including directed growth along anticlinal cell walls and formation of T-shaped branches, infection cushion formation and stomatal penetration. Weak or non-aggressive AGs (R. solani AG 5, AG 3 and binucleate Rhizoctonia AG K) required more time, notwithstanding all AGs were able to penetrate cauliflower hypocotyls. Histopathological observations indicated that Rhizoctonia AGs provoked differential host responses and pectin degradation. We demonstrated the pronounced deposition of phenolic compounds and callose against weak and non-aggressive AGs which resulted in a delay or complete block of the host colonization. Degradation of pectic compounds was observed for all pathogenic AGs, except for AG 2-2 IIIb. Ranking the AGs based on infection rate, level of induced host responses and pectin degradation revealed a strong correlation with the disease severity caused by the AGs.

Conclusion: The differences in aggressiveness towards cauliflower observed among Rhizoctonia AGs correlated with the infection rate, induction of host defence responses and pectin breakdown. All Rhizoctonia AGs studied penetrated the plant tissue, indicating all constitutive barriers of cauliflower were defeated and differences in aggressiveness were caused by inducible defence responses, including cell wall fortifications with phenolic compounds and callose.

Show MeSH

Related in: MedlinePlus

Degradation of cauliflower cell walls by extracellular produced pectic enzymes of seven R. solani AGs and one binucleate Rhizoctonia AG. Microscopic observations of pectic components in cauliflower cotyledones visualized with ruthenium red (I, III, V & VII) and toluidine blue (II, IV, VI & VIII) staining after 24 h incubation in sterile culture filtrate of liquid pectin medium inoculated with a sterile PDA plug as control treatment (I & II), inoculated with R. solani AG 3 (III & IV), inoculated with R. solani AG 4 HGII (V & VI), after 24 h incubation in sterile culture filtrate of liquid cauliflower medium inoculated with R. solani AG 4 HGII (VII & VIII). Scale bars = 50 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2719643&req=5

Figure 2: Degradation of cauliflower cell walls by extracellular produced pectic enzymes of seven R. solani AGs and one binucleate Rhizoctonia AG. Microscopic observations of pectic components in cauliflower cotyledones visualized with ruthenium red (I, III, V & VII) and toluidine blue (II, IV, VI & VIII) staining after 24 h incubation in sterile culture filtrate of liquid pectin medium inoculated with a sterile PDA plug as control treatment (I & II), inoculated with R. solani AG 3 (III & IV), inoculated with R. solani AG 4 HGII (V & VI), after 24 h incubation in sterile culture filtrate of liquid cauliflower medium inoculated with R. solani AG 4 HGII (VII & VIII). Scale bars = 50 μm.

Mentions: Under the in vitro conditions tested in this study, all Rhizoctonia AGs were capable of producing pectic enzymes which reduced the staining intensity of ruthenium red and toluidine blue (Fig. 2). Compared with the cotyledons of the control treatment, for which both staining protocols resulted in a specific coloration of the cell walls, the cotyledons incubated in the culture filtrate of the eight Rhizoctonia AGs showed a clear degradation of the cell walls, including degradation of pectic compounds as indicated by the absence of ruthenium red staining and pink or purple staining by toluidine blue. No differences were observed between isolates of pathogenic and non-pathogenic AGs, suggesting all isolates produced pectinolytic enzymes that could degrade pectin of cauliflower. Because the extracellular production of pectin degrading enzymes depends upon the growth medium [29], two different liquid media were tested; one which contained citrus pectin and one with cauliflower cell walls. Only the isolate of AG 4 HGII yielded different results for the two media. The culture filtrate of the AG 4 HGII isolate grown on pectin medium did not cause a degradation of pectin, while for the culture filtrate of the cauliflower cell wall medium a clear degradation of the cotyledonous cell walls was detected.


Interactions between cauliflower and Rhizoctonia anastomosis groups with different levels of aggressiveness.

Pannecoucque J, Höfte M - BMC Plant Biol. (2009)

Degradation of cauliflower cell walls by extracellular produced pectic enzymes of seven R. solani AGs and one binucleate Rhizoctonia AG. Microscopic observations of pectic components in cauliflower cotyledones visualized with ruthenium red (I, III, V & VII) and toluidine blue (II, IV, VI & VIII) staining after 24 h incubation in sterile culture filtrate of liquid pectin medium inoculated with a sterile PDA plug as control treatment (I & II), inoculated with R. solani AG 3 (III & IV), inoculated with R. solani AG 4 HGII (V & VI), after 24 h incubation in sterile culture filtrate of liquid cauliflower medium inoculated with R. solani AG 4 HGII (VII & VIII). Scale bars = 50 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2719643&req=5

Figure 2: Degradation of cauliflower cell walls by extracellular produced pectic enzymes of seven R. solani AGs and one binucleate Rhizoctonia AG. Microscopic observations of pectic components in cauliflower cotyledones visualized with ruthenium red (I, III, V & VII) and toluidine blue (II, IV, VI & VIII) staining after 24 h incubation in sterile culture filtrate of liquid pectin medium inoculated with a sterile PDA plug as control treatment (I & II), inoculated with R. solani AG 3 (III & IV), inoculated with R. solani AG 4 HGII (V & VI), after 24 h incubation in sterile culture filtrate of liquid cauliflower medium inoculated with R. solani AG 4 HGII (VII & VIII). Scale bars = 50 μm.
Mentions: Under the in vitro conditions tested in this study, all Rhizoctonia AGs were capable of producing pectic enzymes which reduced the staining intensity of ruthenium red and toluidine blue (Fig. 2). Compared with the cotyledons of the control treatment, for which both staining protocols resulted in a specific coloration of the cell walls, the cotyledons incubated in the culture filtrate of the eight Rhizoctonia AGs showed a clear degradation of the cell walls, including degradation of pectic compounds as indicated by the absence of ruthenium red staining and pink or purple staining by toluidine blue. No differences were observed between isolates of pathogenic and non-pathogenic AGs, suggesting all isolates produced pectinolytic enzymes that could degrade pectin of cauliflower. Because the extracellular production of pectin degrading enzymes depends upon the growth medium [29], two different liquid media were tested; one which contained citrus pectin and one with cauliflower cell walls. Only the isolate of AG 4 HGII yielded different results for the two media. The culture filtrate of the AG 4 HGII isolate grown on pectin medium did not cause a degradation of pectin, while for the culture filtrate of the cauliflower cell wall medium a clear degradation of the cotyledonous cell walls was detected.

Bottom Line: We demonstrated the pronounced deposition of phenolic compounds and callose against weak and non-aggressive AGs which resulted in a delay or complete block of the host colonization.Degradation of pectic compounds was observed for all pathogenic AGs, except for AG 2-2 IIIb.Ranking the AGs based on infection rate, level of induced host responses and pectin degradation revealed a strong correlation with the disease severity caused by the AGs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Laboratory of Phytopathology, Faculty of Bioscience Engineering, Ghent University, Coupure Links, 653, B-9000 Gent, Belgium. joke.pannecoucque@ugent.be

ABSTRACT

Background: The soil borne fungus Rhizoctonia is one of the most important plant pathogenic fungi, with a wide host range and worldwide distribution. In cauliflower (Brassica oleracea var. botrytis), several anastomosis groups (AGs) including both multinucleate R. solani and binucleate Rhizoctonia species have been identified showing different levels of aggressiveness. The infection and colonization process of Rhizoctonia during pathogenic interactions is well described. In contrast, insights into processes during interactions with weak aggressive or non-pathogenic isolates are limited. In this study the interaction of cauliflower with seven R. solani AGs and one binucleate Rhizoctonia AG differing in aggressiveness, was compared. Using microscopic and histopathological techniques, the early steps of the infection process, the colonization process and several host responses were studied.

Results: For aggressive Rhizoctonia AGs (R. solani AG 1-1B, AG 1-1C, AG 2-1, AG 2-2 IIIb and AG 4 HGII), a higher developmental rate was detected for several steps of the infection process, including directed growth along anticlinal cell walls and formation of T-shaped branches, infection cushion formation and stomatal penetration. Weak or non-aggressive AGs (R. solani AG 5, AG 3 and binucleate Rhizoctonia AG K) required more time, notwithstanding all AGs were able to penetrate cauliflower hypocotyls. Histopathological observations indicated that Rhizoctonia AGs provoked differential host responses and pectin degradation. We demonstrated the pronounced deposition of phenolic compounds and callose against weak and non-aggressive AGs which resulted in a delay or complete block of the host colonization. Degradation of pectic compounds was observed for all pathogenic AGs, except for AG 2-2 IIIb. Ranking the AGs based on infection rate, level of induced host responses and pectin degradation revealed a strong correlation with the disease severity caused by the AGs.

Conclusion: The differences in aggressiveness towards cauliflower observed among Rhizoctonia AGs correlated with the infection rate, induction of host defence responses and pectin breakdown. All Rhizoctonia AGs studied penetrated the plant tissue, indicating all constitutive barriers of cauliflower were defeated and differences in aggressiveness were caused by inducible defence responses, including cell wall fortifications with phenolic compounds and callose.

Show MeSH
Related in: MedlinePlus