Laboratory experiments were conducted to examine the effect of charcoal addition on N 2 O emissions resulting from rewetting of air-dried soil. Rewetting the soil at 73% and 83% of the water-filled pore space (WFPS) caused a N 2 O emission peak 6 h after the rewetting, and the cumulative N 2 O emissions throughout the 120-h incubation period were 11 ± 1 and 13 ± 1 mg N m −2 , respectively. However, rewetting at 64% WFPS did not cause detectable N 2 O emissions (−0.016 ± 0.082 mg N m −2 ), suggesting a severe sensitivity to soil moisture. When the soils were rewetted at 73% and 78% WFPS, the addition of charcoal to soil at 10 wt% supressed the N 2 O emissions by 89% . In contrast, the addition of the ash from the charcoal did not suppress the N 2 O emissions from soil rewetted at 73% WFPS. The addition of charcoal also significantly stimulated the N 2 O emissions from soil rewetted at 83% WFPS compared with the soil without charcoal addition (P < 0.01). Moreover, the addition of KCl and K 2 SO 4 did not show a clear difference in the N 2 O emission pattern, although Cl − and , which were the major anions in the charcoal, had different effects on N 2 O-reducing activity. These results indicate that the suppression of N 2 O emissions by the addition of charcoal may not result in stimulation of the N 2 O-reducing activity in the soil because of changes in soil chemical properties.

Previous studies have described the development of control methods against bacterial wilt diseases caused by Ralstonia solanacearum. This review focused on recent advances in control measures, such as biological, physical, chemical, cultural, and integral measures, as well as biocontrol efficacy and suppression mechanisms. Biological control agents (BCAs) have been dominated by bacteria (90%) and fungi (10%). Avirulent strains of R. solanacearum, Pseudomonas spp., Bacillus spp., and Streptomyces spp. are well-known BCAs. New or uncommon BCAs have also been identified such as Acinetobacter sp., Burkholderia sp., and Paenibacillus sp. Inoculation methods for BCAs affect biocontrol efficacy, such as pouring or drenching soil, dipping of roots, and seed coatings. The amendment of different organic matter, such as plant residue, animal waste, and simple organic compounds, have frequently been reported to suppress bacterial wilt diseases. The combined application of BCAs and their substrates was shown to more effectively suppress bacterial wilt in the tomato. Suppression mechanisms are typically attributed to the antibacterial metabolites produced by BCAs or those present in natural products; however, the number of studies related to host resistance to the pathogen is increasing. Enhanced/modified soil microbial communities are also indirectly involved in disease suppression. New promising types of control measures include biological soil disinfection using substrates that release volatile compounds. This review described recent advances in different control measures. We focused on the importance of integrated pest management (IPM) for bacterial wilt diseases.

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Bradyrhizobium sp. S23321 is an oligotrophic bacterium isolated from paddy field soil. Although S23321 is phylogenetically close to Bradyrhizobium japonicum USDA110, a legume symbiont, it is unable to induce root nodules in siratro, a legume often used for testing Nod factor-dependent nodulation. The genome of S23321 is a single circular chromosome, 7,231,841 bp in length, with an average GC content of 64.3%. The genome contains 6,898 potential protein-encoding genes, one set of rRNA genes, and 45 tRNA genes. Comparison of the genome structure between S23321 and USDA110 showed strong colinearity; however, the symbiosis islands present in USDA110 were absent in S23321, whose genome lacked a chaperonin gene cluster (groELS3) for symbiosis regulation found in USDA110. A comparison of sequences around the tRNA-Val gene strongly suggested that S23321 contains an ancestral-type genome that precedes the acquisition of a symbiosis island by horizontal gene transfer. Although S23321 contains a nif (nitrogen fixation) gene cluster, the organization, homology, and phylogeny of the genes in this cluster were more similar to those of photosynthetic bradyrhizobia ORS278 and BTAi1 than to those on the symbiosis island of USDA110. In addition, we found genes encoding a complete photosynthetic system, many ABC transporters for amino acids and oligopeptides, two types (polar and lateral) of flagella, multiple respiratory chains, and a system for lignin monomer catabolism in the S23321 genome. These features suggest that S23321 is able to adapt to a wide range of environments, probably including low-nutrient conditions, with multiple survival strategies in soil and rhizosphere.

The primers PCN280f and NEPCN398r were designed for the quantitative detection of the potato-cyst nematode Globodera rostochiensis using real-time polymerase chain reaction (PCR). One, five, 50, 125 and 250 individuals of the second-stage juveniles (J2) of G. rostochiensis were mixed with various stages of vermiform Caenorhabditis elegans to make a total of 500 individuals and DNA was extracted from the nematode mixture. There was a significant correlation (r 2 = 0.9355, P < 0.001) between the threshold cycle values and the number of G. rostochiensis added. When nematodes were extracted from soils artificially infested with G. rostochiensis to various degrees and real-time PCR was conducted using DNA templates from the nematodes extracted, there was a highly significant correlation in the numbers of G. rostochiensis J2 from the real-time PCR method and morphological identification. Real-time PCR sensitively detected a single G. rostochiensis J2 out of 1,000 individuals of free-living nematodes. Similarly, real-time PCR primers RKNf and RKNr were designed for the detection of the root-knot nematode Meloidogyne incognita. This study demonstrated that the real-time PCR assay for the potato-cyst nematode and the root-knot nematode provides a sensitive and reliable means for the rapid quantification of these vermiform pests.