Effective microorganisms" (EM) are a poorly defined mixture of supposedly beneficial microorganisms that are claimed to enhance microbial turnover in compost and soil. In Costa Rica, EM are used to produce organic compost (bokashi) from banana residues (Musa ssp.). Given the scarcity of scientific data about the effects of EM on the mineralization of plant residues, this study aimed at investigating the effects of EM addition on the decomposition of banana residues during Bokashi production. To this end, the following non-EM treatments were compared to EM Bokashi: Bokashi produced with water (W), with molasses (M) as an EM additive, and with sterilized EM (EMst). Subsequently, the effects of the resulting Bokashi treatments on the growth of young banana plants were evaluated. Compared with non-EM controls, the effect of EM on the mineralization of banana material was negligible. Dry-matter losses of the composts with different EM treatments were similar, with about 78% over 5 weeks. Ergosterol concentration was highest in EM Bokashi (77 lg (g dry soil) -1 ) and lowest in EMst Bokashi (29 lg (g dry soil) -1 ). Microbial biomass carbon (C mic ) and microbial biomass nitrogen (N mic ) were both lowest in EM (C mic = 3121 lg g -1 ; N mic = 449 lg g -1 ), while C mic was highest in Bokashi produced with molasses (3892 lg g -1 ) and N mic was highest in EMst (615 lg g -1 ). Treatment effects on adenylate concentrations and adenylate energy charge were negligible. Application of all Bokashi variants to young banana plants significantly increased shoot growth under greenhouse conditions compared to plants grown in a control soil without amendments. However, these effects were similar for all Bokashi treatments, even if EM Bokashi increased the K concentrations in banana leaves significantly compared to Bokashi produced with EMst and the control. Bokashi produced with only molasses and EM Bokashi decreased the number of root nematodes under greenhouse conditions compared to the control. Overall, the results confirmed the expected influence of composting on the degradation of organic material and the effect of compost application on plant growth. Hower, under the conditions of this study, EM showed no special effects in this, except for increasing the K concentrations in the leaves of young banana plants.
Transmission of Xanthomonas manihotis in botanical seeds of cassava was studied by direct immunofluorescence and enzyme-linked immunosorbent assays. The pathogen was detected in seed embryos and in pollen but not in other tissues of cassava seeds. Healthy and infected seeds showed no signs of damage due to X. manihotis, but approximately 104 cells/ml were detected in infected embryos. Seed transmission varied from 0 to 40%.
Disease surveys conducted in Trinidad between 1985—1987 showed that Cassava Bacterial Blight (CBB) is present in all but one county of the country with disease severity ratings varying from 1—5 depending on day/night temperatures. Field and greenhouse screening identified varieties such as Point Fortin fine leaf and CMC 40 as being resistant whereas M col 22 was moderately resistant to susceptible. Using a combination of antiserum produced to whole cells of Xanthomonas campestris pv. manibotis and a broth enrichment technique, dissemination of the pathogen by flood water was confirmed. The pathogen was detected at distances of up to 300 meters from infected fields. The significance of this mode of pathogen dissemination in initiating primary infection in Trinidad is discussed.
SUMMARY
Fungicide treatment of soil and true potato seed and the use of subsoil as a growth medium significantly reduced pre‐emergence damping‐off caused by Rhizoctonia solani. Attempts were made to determine safe levels of fungicides for soil and seed treatments. For seed, safe levels varied between 0–9% a.i. for pentachloronitrobenzene (PCNB) and 3‐0% a.i. for mancozeb (dithane M‐45).
Fungicides only marginally reduced post‐emergence damping‐off of transplants raised from true potato seed but gave significant increase in yield. The prospects of using fungicide treatment of true seed to control damping‐off in seed beds and in direct field sowing are discussed.
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