[in Japanese]

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[in Japanese]

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[in Japanese]

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Rot symptoms are serious yield loss factors in the production of lotus in Tokushima Prefecture, Japan. The objective of this study was to evaluate the effects of solarization on soil temperature, the density of F. oxysporum, one of the causal agents of rot symptoms, and lotus yields in different fields in Tokushima Prefecture. A survey demonstrated a significant relationship between the densities of F. oxysporum and occurrences of lotus rhizome rot. Average soil temperatures at a depth of 15 cm were 25.5°C and 29.3°C in control and solarized fields, respectively. The maximum soil temperature was 34.3°C in control and 41.4°C in solarized fields. Cumulative times above 30°C were 28–70 h in control and 81–1079 h in solarized fields. Significant reductions in the densities of F. oxysporum were observed in solarized fields but not in non-solarized fields. Solarization improved yields of lotus: the average yield was increased by 79% as compared to that of the previous cropping season. The present study revealed that solarization reduced the density of F. oxysporum in soil and, thereby, increased lotus yield.

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One hundred twenty antibiosis-positive and 34 antibiosis-negative heat-resistant bacteria (Bacillus spp.) were isolated from the surface-sterilized roots and the rhizosphere soils of tomato seedlings grown in Afghanistan soils and evaluated for their biocontrol potential against the root-knot nematode Meloidogyne incognita. Firstly, antibiosis properties of the isolates were tested using the tomato Fusarium-wilt pathogen. Then, effects of culture-filtrates of the selected isolates on the second stage juveniles (J2) mortality and egg-hatch were evaluated. Among antibiosis-positive isolates, 12 showed significantly higher J2 mortality (83.6 ± 1.5%) and lower egg-hatch (14.2 ± 2.3%) and were selected for further experiments using tomato plants. Antibiosis-negative isolates showed relatively lower J2 mortality (30.9 ± 7.6%). The antibiosis-positive isolates Kh2-27, Kh2-30, B7-2, and B1-6 decreased the nematode damages to tomato plant by 57.7%, 55.8%, 57.7% and 61.5%, respectively. The other eight isolates also significantly decreased damage to tomato plant. The antibiosis-negative isolates Kh2-5 and B7-12 also decreased the root-knot disease to a similar degree to those of the antibiosis-positive isolates, suggesting that antibiosis was not the main factor for the root-knot disease suppression. Phylogenetic analysis based on the 16S rDNA sequences and the physiological properties indicated that the antibiosis-positive isolates are closely related to B. subtilis and B. tequilensis. The two antibiosis-negative isolates were closely related to B. megaterium species. These results indicate the capability of heat-resistant bacteria as a biocontrol tool for the management of the root-knot nematode under local environmental conditions in Afghanistan.

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Sclerotia of Cenococcum geophilum tend to be particularly abundant near its mycorrhiza as spherical grains of about 0.05–4 mm in diameter. In this study, we examined sclerotium propagules to investigate the persistent structure of sclerotia in forest soils. Sclerotia were collected from the surface A horizon of Luvisols in the Harz Mountains (HRZ) of central Germany, Podsols on Mount Ontake in central Japan, and Andosols on the Lake Tazawa plateau in northeastern Japan. For comparison, we examined sclerotia from the surface and buried humic layer beneath tephra of an 11th-century eruption of Mount Myoko in central Japan. The sclerotia from the different study areas basically resembled each other, although HRZ sclerotia exhibited the greatest physical strength. On the basis of sclerotia bulk density, Fourier transform infrared spectrum, and accelerator mass spectrometry ¹⁴C ages, we conclude that young and fresh cell material of HRZ sclerotia support their physical strength. The physical strength of the sclerotia could be initially regulated by internal structure and cell wall properties (e.g., thickness, chemical composition, and confluency of cells), which might be differentiated by genetic variation. The length of time spent in soil and decomposition intensity, which can be regulated by the soil environment, may be secondary factors regulating the physicochemical characteristics of sclerotia

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