Evidence that the biofungicide Serenade (Bacillus subtilis) suppresses clubroot on canola via antibiosis and induced host resistance

This study investigated how the timing of application of the biofungicide Serenade (Bacillus subtilis QST713) or it components (product filtrate and bacterial cell suspension) influenced infection of canola by Plasmodiophora brassicae under controlled conditions. The biofungicide and its components were applied as a soil drench at 5% concentration (vol/vol or equivalent CFU) to a planting mix infested with P. brassicae at seeding or at transplanting 7 or 14 days after seeding (DAS) to target primary and secondary zoospores of P. brassicae. Quantitative polymerase chain reaction (qPCR) was used to assess root colonization by B. subtilis as well as P. brassicae. The biofungicide was consistently more effective than the individual components in reducing infection by P. brassicae. Two applications were more effective than one, with the biofungicide suppressing infection completely and the individual components reducing clubroot severity by 62 to 83%. The biofungicide also reduced genomic DNA of P. brassicae in canola roots by 26 to 99% at 7 and 14 DAS, and the qPCR results were strongly correlated with root hair infection (%) assessed at the same time (r = 0.84 to 0.95). qPCR was also used to quantify the transcript activity of nine host-defense-related genes in inoculated plants treated with Serenade at 14 DAS for potential induced resistance. Genes encoding the jasmonic acid (BnOPR2), ethylene (BnACO), and phenylpropanoid (BnOPCL and BnCCR) pathways were upregulated by 2.2- to 23-fold in plants treated with the biofungicide relative to control plants. This induced defense response was translocated to the foliage (determined based on the inhibition of infection by Leptosphaeria maculans). It is possible that antibiosis and induced resistance are involved in clubroot suppression by Serenade. Activity against the infection from both primary and secondary zoospores of P. brassicae may be required for maximum efficacy against clubroot.

Effect of Moisture and Temperature on Disease of Green Foxtail Caused by Drechslera gigantea and Pyricularia setariae

Leaf wetness duration, temperature, intermittent leaf wetness, and delayed leaf wetness were investigated for their influence on disease of green foxtail caused by Drechslera gigantea and Pyricularia setariae to determine the potential of these two fungi as bioherbicide agents in the Canadian prairies. For both fungi, disease severity increased with increasing leaf wetness duration at 15, 20, 25, 30, and 32°C. At 10°C, conidia of both fungi showed minimal germination, regardless of leaf wetness duration; however, an increase in conidial germination, appressoria formation, and disease occurred at 15°C. Conidia of both species showed 80% or greater germination at all temperatures above 15°C, whereas the optimum temperatures for appressoria formation by D. gigantea and P. setariae were 23 and 25°C, respectively. Maximum disease occurred after 48 h of leaf wetness at 32°C for D. gigantea and at 25°C for P. setariae. Disease caused by both fungi decreased when 4 h of continuous leaf wetness was followed by a 20-h dry period, and after an 8-h delay in leaf wetness following inoculation. Both fungi required immediate and prolonged periods of leaf wetness at temperatures of 15°C and above to cause severe disease on green foxtail. The moisture requirements of these fungi may limit their effectiveness as bioherbicide agents in the semi-arid Canadian prairies.

Soil microbial populations, community composition, and activity as affected by repeated applications of hog and cattle manure in eastern Saskatchewan

A field site near Humboldt, Saskatchewan, was annually treated with hog or cattle manure and cropped to canola, spring wheat, barley, and canola from 1997 to 2000. During each growing season, soil was analyzed for microbial populations in terms of activity and community structure, and crops were assessed for root rot and foliar diseases. Microbial activity in soils treated with cattle manure was higher than in soils treated with hog manure or urea. Similarly, nitrous oxide emissions from soil increased with increasing rates of hog and cattle manure. Potential human pathogens, including Rahnella, Serratia, Proteus, Leclercia, and Salmonella species, were identified in soils that received cattle manure, whereas pseudomonads were the dominant species in the hog-manure-treated soil. Fecal coliforms were confirmed in soils that received hog or cattle manure. However, Enterobacteriaceae populations were 10-fold higher in soils receiving cattle manure than in soils receiving the other treatments. Increasing cattle manure rates increased fecal coliform population, but there was no indication that increased hog manure rates increased fecal coliform populations. Addition of urea, hog manure, or cattle manure to the soil did not increase foliar disease in wheat, barley, and canola and had variable effects on root rot incidence in cereals.

Occurrence of Vesicular-Arbuscular Mycorrhizal Fungi in Alberta, Canada

Three V A mycorrhizal fungal species were isolated from soils in Alberta, Canada and examined by scanning electron microscopy and energy-dispersive X-ray microanalysis. Mature spores of Glomus aggregatum developed an outer hyaline wall which contained lower levels of calcium than the middle wall. Examination of G. pansihalos spores revealed a lower level of calcium in the outer evanescent wall as compared to the ornamented wall. When spores of Entrophospora infrequens were examined, the wall of the vesicle was found to contain similar levels of calcium as the ornamented wall of the spore. The significance of the results concerning the presence of calcium in mycorrhizal spore walls is discussed, as is the occurrence of the mycorrhizal species.

A new species of Glomus (Endogonaceae, Zygomycotina) mycorrhizal with barley in Alberta

A new species of endogonaceous fungus mycorrhizal with barley in Alberta is described. Glomus dimorphicum sp. nov. has two types of spores formed singly and in loose, often radiately arranged clusters. This new species produces very few vesicles, and arbuscule formation has so far not been observed.