Daigo Aiuchi

Future Biological Control for Soybean Cyst Nematode

Masanori Koike1, Ryoji Shinya2, Daigo Aiuchi3, Manami Mori1, Rui Ogino1, Hiroto Shinomiya1, Masayuki Tani1 and Mark Goettel4 1Department of Agro-environmental Science Obihrio University of Agriculture & Veterinary Medicine 2Graduate School of Agriculture, Kyoto University 3National Research Center of Protozoan Disease Obihrio University of Agriculture & Veterinary Medicine 4Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge 1,2,3Japan 4Canada

Lack of yield response in potato (Solanum tuberosum L.) to phosphate fertilizer under contrasting soil types varying in phosphate absorption coefficient and available phosphate

ABSTRACT There is growing evidence of excessive use of phosphate fertilizer and high residual soil phosphate levels in arable cropping systems in Japan. However, there is a lack of regional-scale information on the current status of soil-available phosphate as well as its impacts on a potato (Solanum tuberosum L.) cropping system. Although phosphorus is an essential nutrient, there have been confounding reports about the effects of excessive soil-available phosphate on potato tuber yields. This study was conducted in Hokkaido, Japan, to determine the current status of phosphate fertilizer application rate and soil-available phosphate levels, and their effects on tuber yield. In two contrasting soil types varying in phosphate absorption coefficient (PAC), soil and potato tuber samples were collected from 90 and 80 grower fields in Tokachi and Kamikawa districts, respectively, in the 2013 and 2014 growing seasons. The soil samples were analyzed for PAC, available phosphate by the Truog method, and total phosphate along with total carbon and acid-oxalate extractable aluminum. The tuber samples were collected at the harvesting stage for the calculation of yields. This study revealed (1) ongoing excessive phosphate fertilization regardless of high soil-available phosphate levels in potato-producing fields of Hokkaido, (2) no positive impacts of excess soil-available phosphate on tuber yields, and (3) no yield response from the applied phosphate fertilizer in excess of the recommended rate in two contrasting soil types. In conclusion, excess phosphate fertilizer was an unnecessary cost to the growers and could also be a potential harm to the environment, and changes are urgently needed to optimize the input–output balance of phosphate in this agricultural system.

Proboscis infection route of Beauveria bassiana triggers early death of Anopheles mosquito

Entomopathogenic fungi are known to control vector mosquito populations. Thus, understanding the infection dynamics of entomopathogenic fungi is crucial for the effective control of insect pests such as mosquitoes. We investigated the dynamics of Beauveria bassiana s.l. 60-2 infection of Anopheles stephensi by exposing the mosquito to fungus-impregnated filter paper through two infection routes and then comparing the mortality and extent of infection. Fungal development was observed after using this inoculation method with both the tarsus route and the proboscis route, but early mosquito death occurred only after infection through the proboscis route. Fungal hyphae invaded almost all the tissues and organs before or after the death of the host, and fungal invasion of the brain was highly correlated with mortality. Moreover, although all mosquitoes that were alive at various time points after inoculation showed no fungal infection in the brain, fungal infection was detected in the brain in all dead mosquitoes. Our results suggest that fungal invasion of the brain represents one of the factors affecting mortality, and that the proboscis route of infection is critical for the early death of vector mosquitoes.

A selective medium to isolate airborne spores of Microdochium nivale, causing winter wheat scab

Winter wheat scab in Hokkaido, Japan is caused predominantly by Gibberella zeae and Microdochium nivale and can result in significant yield losses. A selective medium for isolation of G. zeae was previously developed, but not for M. nivale. The purpose of this study therefore was to develop a selective medium for isolation of airborne spores of M. nivale. Based on the basic composition of Komada’s Fusarium-selective medium, carbon and nitrogen sources and the most suitable vitamin B component for the basal composition were examined. Hyphal growth of M. nivale was promoted when galactose was replaced with lactose and combined with L-asparagine, while aerial hyphal formation increased with thiamine hydrochloride as the vitamin B source. In antimicrobial composition, colony formation of other filamentous fungi was greatly inhibited by spiroxamine. Thiophanate methyl, to which M. nivale shows resistance, selectively inhibited the growth of Fusarium spp. only. Spore trapping using the selective medium was subsequently performed in a wheat field. M. nivale formed characteristic pinkish colonies on the selective medium in the case of contamination with other filamentous fungi, making differentiation easy. Overall, the findings show that LATTS medium developed in this study is effective for isolation of airborne spores of M. nivale.