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Japan Late Blight Report

1. Late blight occurrence and LB severity by major production area in the country. What crops were affected (tomato, potato, others)? Disease sources (seed, cull piles, volunteer plants, soil)?

Late blight is common throughout the potato growing regions and progresses very rapidly under cool and wet conditions.

2. LB impact (foliar damage, yield losses, tuber rot occurrences)?  

Without chemical control both foliar and tuber blight can occur throughout the potato producing areas. Yield losses in susceptible cultivars without chemical control can reach 30%. In Hokkaido, tuber blight can cause severe losses occasionally.

3. Fungicide use (amounts, types, etc.)?

4. Other LB control measures (resistant cultivars, forecast systems, none)?

The commercial cultivar ‘Hanashibetsu’ is highly resistant to late blight and can be grown with reduced fungicide applications in some regions. FLABS, a forecasting system for outbreak of late blight, is used in Hokkaido. The validity of Blitecast and Simcast is now under investigation.

5. LB control effectiveness (fungicide or host resistance failures)?

During the past decade two field cultivars, ‘Matilda’ and ‘Hanashibetsu’, were released as commercial cultivars. These cultivars were so highly resistant to late blight that they were considered suitable for farming with reduced or no application of fungicides. ‘Matilda’ was exclusively grown in Memuro town, at the central part of Tokachi district, Hokkaido region [the northernmost island of Japan]. However, ‘Matilda’ blighted unusually earlier in 1998 than the previous years and the reason for weakened field resistance was unknown. As explained below, there is evidence that the population of P. infestans had changed.

A study of P.infestans isolates collected throughout the country in 1988 found that only A2 mating type isolates were resistant to metalaxyl. Since late 1990s, new genotypes expanded in Hokkaido. The predominant genotypes are resistant or intermediately resistant to metalaxyl.

6. Pathogen strains (mating type, fungicide resistance, virulence factors, etc)?

Comparisons of the isoenzyme analysis of P. infestans isolates prior to 1987 and those collected from many locations during 1987-1990 provided evidence of a change in the population genetic structure. The A2 mating type predominated in 1989 in all regions except Tohoku, which is located immediately below the northernmost district of Tokachi, Hokkaido region, a major potato producing area. The proportion of the genotype JP-1 (A2 mating type) increased from 54% in 1987 to 97% in 1993.

After 1995, new genotypes occurred and expanded their distribution in Hokkaido. Before 1997, the genotype JP-1 was highly predominant in the Tokachi district. Genotype A (mating type A1) was detected for the first time in Tokachi during 1998–1999 and increased to 72% of the P. infestans isolates collected 1999. Genotype A produced more lesions on the highly resistant cultivar `Matilda´ than the genotype JP-1 or the genotype B using spray inoculation of sporangial suspension, but all the three genotypes produced progressing lesions using drop inoculation. The results suggest that the reduced field resistance of `Matilda´ was due to the spread of genotype A to Memuro town, where the cultivar was grown

7. Disease risks and/or major needs?

8. Any publications on late blight in the country?

Kato M and Shimanuki T .2002. Reduction of fungicide applications by field resistant cultivars to potato late blight. pp 161 in: Lizárraga C (ed), Late blight: Managing the global threat. Proceedings of the Global Initiative on Late Blight Conference, Hamburg, Germany, 11–13 July 2002. International Potato Center, Lima, Peru.

Kato M and Naito S. 2001. Change of predominant genotypes of Phytophthora infestans in Tokachi district, Hokkaido, Japan and difference of lesion productivity to the field resistant cultivar “Matilda” among genotypes. Journal of Agricultural University of Hebei, China Vol. 24 (2): 11–15. Proceedings of the GILB East and Southest Asia Linkage Group workshop on late blight, 16–20 August, Baoding Hebei, China.

Kato M and Naito S. 1998. Occurrence of new strains of A1 mating types after displacement of an A1 strain by an A2 strain of Phytophthora infestans in Japan, 7^th International Congress of Plant Pathology , 9–16 August 1998, Edinburgh, Scotland, Abstract 22.80.

Kato M, Sato N, Takahashi K, et al.1998. Yearly change of frequency and geographical distribution of A2 mating type isolates of Phytophthora infestans in Japan from 1987 to 1993. Annals Phytopathological Society Japan 64:168–174.

Kato M, Mosa A A , Sato N, et al. 1992. Cultural features associated with mating types of  Phytophthora infestans isolates from potato crops in Japan. Annals Phytopathological Society Japan 58:265–275.

Kato M, Mosa A A , Sato N, et al. 1992. Cultural features associated with mating types of  Phytophthora infestans isolates from potato crops in Japan. Annals Phytopathological Society Japan 58:265–275.

Kishi K. 1962. Studies on the physiological specialization of Phytophthora infestans on tomatoes. 1: On the tomato intermediate and potato types of Phytophthora infestans. Annals Phytopathological Society Japan. 27:172–179.

Mosa A A, Kato M, Sato N, Kobayashi K and Ogoshi, A. 1989. Occurrence of the A2 mating type of Phytophthora infestans on potato in Japan. Annals Phytopathological Society Japan 55:615–620.

Mosa A A, Kabayashi K, OgoshiI A, Kato M and Sato N. 1993. Isoenzyme and segregation in isolates of Phytophthora infestans from Japan. Plant Pathology 42:26–34.

Sato N. 1980. Sources of inoculum and sites of infection of potato tubers by Phytophthora infestans in soil. Annals Phytopathology Society Japan 46:231–240.

Sato N and KATO M. 1993. Improvement of the selective medium and method for the isolation of  Phytophthora infestans. Annals Phytopathological Society Japan 59:568–571.

Sato N, Kato M, Osa A A, et al. 1991. A newspaper bag method for sample collection of blighted potato leaflets for isolation of Phytophthora infestans. Annals Phytopathological Society Japan 57:573–576.

Therrien C D, Tooley P W, Spielman L J, Fry W E, Ritch D L and Shelly S E. 1993 Nuclear DNA content allozyme phenotypes and metalaxyl sensitivity of Phytophthora infestans from Japan. Mycological Research 97:945–950.

9. Is tuber blight an increasing problem?

Yes.

10. Other comments

Recently food crops produced by organic farming and using reduced number of fungicide applications have become popular among consumers. A trend to reduce unnecessary fungicide application is also growing. To satisfy these needs, resistant cultivars are required.

Contact: Masayasu Kato, Japan International Research Center of Agricultural Science. 1-1, Ohwashi, Tsukuba, Ibaraki, Japan. Email: mkato(at)affrc.go.jp