Biocontrol of Sugar Beet Seedling and Taproot Diseases Caused by Aphanomyces cochlioides by Pythium oligandrum Treatments before Transplanting

Abstract

IntroductionIn Japan, sugar beets (Beta vulgaris L.) are only cultivated in the Hokkaido region, where a transplanting technique is commonly employed. This technique entails seeding sugar beets in paper pot nurseries for about 45 days of cultivation in a greenhouse, and then transplanting the seedlings in the field. Commercial fungicide-pelleted seeds are typically used to protect sugar beets from seedling diseases. In the Hokkaido region, Pythium spp., Rhizoctonia solani and Aphanomyces cochlioides are the main causal pathogens at the seedling stage of sugar beet 11 . Infection by Pythium spp. primarily causes pre-emergence damping-off, while R. solani causes the pre-emergence death of seedlings and damages newly emerged seedlings. On the other hand, A. cochlioides causes little or no preemergence damping-off, but causes extensive post-emergence damping-off that could result in the destruction of entire fields, especially in warm and wet soil 13 . Fungicidepelleted seeds can stably control pre-emergence damping-off, but not post-emergence damping-off, and so the latter type of damping-off caused by A. cochlioides is the main cause of sugar beet seedling loss. Furthermore, after seedlings are transplanted in the field, A. cochlioides can also cause root rot (i.e., Aphanomyces root rot) from late June to the end of the growing season 28,29 . The pathogen is widely distributed throughout sugar beet production areas, persistent for long periods in the soil, and not easily controlled by chemicals and cultivation practices. As a result, Aphanomyces root rot is a chronic problem that could become particularly severe in certain fields or during years when warm and moist conditions prevail. Therefore, new control measures for both post-emergence Biocontrol of Sugar Beet Seedling and Taproot Diseases Caused by Aphanomyces cochlioides by Pythium oligandrum AbstractBiocontrol activities in the oospore suspensions of 17 isolates of Pythium oligandrum (PO) were examined for their effect against post-emergence seedling diseases. The seeds of sugar beet that had been commercially chemical-pelleted to prevent pre-emergence damping-off were sown in Aphanomyces cochlioides-infested soil on trays. PO isolate MMR2 proved most effective in controlling post-emergence damping-off, at a level equivalent to that of applying fungicides. Oospore suspensions stored for 188 days or 379 days at 4℃ were as effective against A. cochlioides post-emergence damping-off as chemical control. Treating soil with PO oospores by mixing suspensions into the surface of soil in paper pot nurseries or by drenching seedlings 32 days before transplanting could control Aphanomyces root rot in the field without additional applications. The control effect conferred by PO suspensions was also demonstrated in vitro. A polymerase chain reaction (PCR) assay used to detect PO indicated that this oomycete could colonize the rhizosphere of sugar beet plants cultivated in the field when applied before transplanting. These results suggest that PO has the potential to c...

Characterization of species associated with Pythium soft rot of ginger and evaluation of Pythium Oligandrum as a biocontrol

“…Our results were consistent with other findings where isolates within the same Pythium sp. might exhibit various degrees of susceptibility or antagonism from P. oligandrum Foley and Deacon, 1986;Takenaka and Ishikawa, 2013). According to Gerbore et al (2014b) soil-borne host pathogens were most vulnerable to mycoparasitism by P. oligandum when the latter was originally recovered from the same rhizospheres as of the pathogens.…”

“…Susceptibility of Pythium spp. to P. oligandrum antagonism can vary greatly among isolates within a species and be influenced by environmental conditions (AlRawahi and Hancock, 1998;Floch et al, 2009;Foley and Deacon, 1986;Takenaka and Ishikawa, 2013). In chapters 4, isolates of P. myriotylum varied in aggressiveness; those recovered from PSR ginger were more aggressive and over a wider temperature range on ginger compared with isolates of P. myriotylum recovered from other host crops.…”

“…and Aphanomyces cochlioides (Abdelzaher et al, 1997;Benhamou et al, 1999;Horner et al, 2012;McQuilken et al, 1990;Ribeiro and Butler, 1995;Takenaka and Ishikawa, 2013). In addition, P. oligandrum has been reported to have the capability of induce disease resistance and promote plant growth of many crops in both in vitro and in vivo studies Brozova, 2002;Gerbore et al, 2014a;Takenaka et al, 2008;Yacoub et al, 2016).…”

“…Of the two seed treatments with P. oligandrum, the pelleting treatment was more effective than the film-coating. However, the protection levels either with fungicidal applications or seed coating with P. oligandrum were still insufficient in controlling damping off in soils with high pathogen potential (McQuilken et al, 1990;Takenaka and Ishikawa, 2013). Al-Rawahi and…”

“…Due to inconsistency in disease control provided by P. oligandrum, it is in general recommended that either multiple applications or co-inoculations of P. oligandrum with other BCAs are more likely to reduce degrees of variability in protection provided by P. oligandrum (Al-Rawahi and Hancock, 1998;Floch et al, 2009;Holmes et al, 1998;Takenaka and Ishikawa, 2013;Gerbore et al, 2014a).…”