Mamoru Satou

Physiological races and vegetative compatibility groups of butterhead lettuce isolates of Fusarium oxysporum f. sp. lactucae in Japan

Races were identified among butterhead lettuce isolates of Fusarium oxysporum f. sp. lactucae collected from three geographical areas of Hokkaido, Shizuoka, and Fukuoka in Japan by inoculation tests using Fujinaga’s race differential cultivars of lettuce (i.e., Patriot, Costa Rica No. 4, and Banchu Red Fire). Eighteen isolates from Shizuoka and Fukuoka were designated race 3, with two unknown vegetative compatibility groups (VCGs) that differed from Ogiso’s VCG 1 and 2. These two new VCGs were obtained from both Shizuoka and Fukuoka. On the other hand, three isolates from Hokkaido were classified as race 1 and identified as VCG 1, which represents a VCG of crisphead isolates from Nagano.

Pathogenicity Groups in Fusarium oxysporum f. sp. lactucae on Horticultural Types of Lettuce Cultivars

Isolates of Fusarium oxysporum f. sp. lactucae obtained from six localities in Japan were divided into three patho-genicity groups. Group 1 was highly pathogenic to lettuce cultivars of crisphead and red leaf types and was less pathogenic to butterhead and green leaf type cultivars. Group 2 was highly pathogenic to butterhead type and less pathogenic to crisphead and leaf types. Group 3 was less pathogenic to all lettuce types than groups 1 and 2. These results indicated pathogenic differentiation in F. oxysporum f. sp. lactucae, roughly relating to horticultural types of host lettuce cultivars.

Development of sequence tagged site markers to identify races of Fusarium oxysporum f. sp. lactucae

By random amplified polymorphic DNA (RAPD) analysis of the representative isolates of each race of Fusarium oxysporum f. sp. lactucae, RAPD fragments of 0.6, 1.6, and 2.9 kb were obtained. The 0.6-kb RAPD fragment was common to the representative isolates of all three races. Amplification of the 1.6- and 2.9-kb fragments were unique to the isolates of races 1 and 2, respectively. Sequence tagged site (STS) marker FLA0001, FLA0101, and FLA0201 were generated from the 0.6-, 1.6-, and 2.9-kb RAPD fragments, respectively. Polymerase chain reaction (PCR) analysis showed that FLA0001 was common to all 49 isolates of F. oxysporum f. sp. lactucae. FLA0101 was specifically generated from all 23 isolates of race 1 but not from races 2 or 3. FLA0201 was specifically amplified from all 12 isolates of race 2 but not from races 1 or 3. In two isolates of F. oxysporum f. sp. lactucum, PCR amplified FLA0001 and FLA0101 but not FLA0201. On the other hand, these STS markers were not detected from isolates of five other formae speciales. Because these STS markers were not generated from isolates of other plant pathogenic fungi, bacteria, or plant materials examined in this study, PCR analysis combined with the three STS markers should be a useful means for rapid identification of races of F. oxysporum f. sp. lactucae.

Cutting rot of chrysanthemum (Chrysanthemum morifolium) caused by Plectosporium tabacinum

Cutting rot of chrysanthemum was found on cuttings of cv. Jimba No.2 in 2008. The cuttings were imported, then transplanted in Aichi Prefecture. Root development was not initiated in about 30% of the cuttings. The cut stem ends developed black discolouration and decay. When healthy cuttings were the fungus isolated from diseased cuttings, these cuttings developed the same disease symptoms. The characteristics and morphology of the fungal culture were identical to those of Plectosporium tabacinum. We propose that the new disease be named cutting rot of chrysanthemum.

Appearance of race Pfs:5 of spinach downy mildew fungus, Peronospora farinosa f. sp. spinaciae, in Japan

The races for the causal agent of spinach downy mildew Peronospora farinosa f. sp. spinaciae were identified by inoculation of race-differential cultivars. One isolate was identified as Pfs:5s and the others belonged to a new race. This is the first report of race Pfs:5 and another new race in Japan.

Leaf mold of tomato caused by races 4 and 4.11 of Passalora fulva in Japan.

Leaf mold of tomato was found on cv. Momotaro-fight in 2003 in Ehime Prefecture. The symptoms were marginal indefinite yellowing on the upper leaf surface, and downy, gray to brown sporulation on the lower surface underneath the spots. The symptoms and morphology were the same as seen with Passalora fulva. The fungal isolates were identified as races 2.4, 2.4.11, 4, and 4.11 by inoculation tests. Races 4 and 4.11 have never before been found in Japan.

A New Race of Spinach Downy Mildew in Japan

A new race of spinach downy mildew caused by Peronospora effusa occurred in Fukui, Japan. The fungus was capable of affecting spinach cultivars resistant to races 1, 2, 3 and 4, but not some other cultivars. Thus, the fungus had different pathogenicity from race 3 and race 4 of the pathogen and was considered to be a new race of spinach downy mildew in Japan.

First report of downy mildew of carnation caused by Peronospora dianthicola in Japan

Yellowish lesions with downy, gray growth developed on the leaves of carnations (Dianthus caryophyllus) in a greenhouse in Hokkaido Prefecture, Japan, in March 2011. We identified the fungus on diseased plants as Peronospora dianthicola on the basis of the morphologies of the conidia, conidiophores, and oospores. To confirm pathogenicity of the fungus, we inoculated healthy plants with a conidial suspension of the fungus, and the plants developed the same signs and symptoms as the naturally infected plants. We then reidentified P. dianthicola from the diseased lesions. This is the first report of downy mildew of carnation in Japan.

First report of spinach downy mildew caused by race Pfs:8 of Peronospora farinosa f. sp. spinaciae in Japan.

The race of field isolates of Peronospora farinosa f. sp. spinaciae (Pfs), causal agent of spinach downy mildew, were identified using race-differential cultivars. One isolate was similar to race Pfs:6. Three isolates were identified as race Pfs:8, the first time the race has been reported in Japan as far as we know. The differential reaction caused by the other two isolates did not match any known to be caused by races Pfs:1 through Pfs:11; thus, this strain appears to a new pathogenic strain in Japan.

First report of downy mildew of statice caused by Peronospora statices in Japan

In June 2013, plants of hybrid statice (Limonium spp.) cultivar Misty Blue in a greenhouse in Hokkaido Prefecture, Japan, were observed to have yellowish leaves with gray to white downy growth on the surface, mainly on the abaxial side. The present report describes the identification of the causal pathogen as Peronospora statices based on its morphology and the internal transcribed spacer of its ribosomal DNA (rDNA-ITS) sequences. After inoculation of statice seedlings with the isolate, the original symptoms were reproduced. This is the first report of downy mildew of statice in Japan.