The genetic relationship between the vegetative compatibility groups (VCGs) and between physiological races of Fusarium oxysporum f. sp. lactucae (FOL), the causal pathogen of lettuce root rot, was determined by analyzing the intergenic spacer (IGS) region of its ribosomal DNA. A total of 29 isolates containing a type strain were tested: 24 Japanese isolates, 2 Californian isolates, and 3 Italian isolates. Three races (races 1, 2, and 3) were found in Japan, and race 1 was also distributed in California and Italy. Races 1, 2, and 3 each belonged to a distinct VCG: VCG-1, VCG-2, and VCG-3 (VCG-3-1, VCG-3-3), respectively. Phylogenetic (neighbor-joining) analysis of the IGS sequences revealed that races 1, 2, and 3 coincided with three phylogenetic groups (PG): PG-1, PG-2, and PG-3, respectively. These results indicate that the three races are genetically quite different and have a strong correlation with VCGs and phylogenetic groupings.

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Although the causal agent of yellows of Brassica rapa (turnip, pak choi, and narinosa) in Japan was reported in 1996 to be Fusarium oxysporum f. sp. conglutinans, this classification has remained inconclusive because of a lack of detailed genetic and pathogenic studies. Therefore, we analyzed the taxonomic position of this organism using Japanese isolates of F. oxysporum complex obtained from diseased individuals of various B. rapa subspecies. Phylogenetic analyses using partial sequences of the rDNA intergenic spacer region and the mating-type gene (MAT1-1-1alpha-box) showed that B. rapa and cabbage isolates belong to different monophyletic clades that separated at early evolutionary stages. Additionally, correlations were observed between the molecular phylogeny and the vegetative compatibility groups. Isolates from turnip, komatsuna, and narinosa (B. rapa group) did not show pathogenicity against cabbage or broccoli (B. oleracea group), although they caused severe symptoms on their original host species. In contrast, cabbage isolates had significantly higher (P = 0.05) virulence on B. oleracea than on B. rapa crops. Our results indicate that F. oxysporum complex isolates from B. rapa and B. oleracea are not only phylogenetically distinct but also differ in host specificity. Therefore, we propose a novel forma specialis, F. oxysporum f. sp. rapae, which causes yellows on B. rapa, including turnip, komatsuna, pak choi, and narinosa.

A new bacterial disease has been observed on pea in Shizuoka prefecture, Japan, since 1981. The disease occurs in early autumn when pea plants grow vigorously. The disease is characterized by chlorosis and whitening of apical shoots, including leaflets, stipules, and young pods. Usually, these white top (WT) symptoms are associated with extensive water-soaked lesions on stems and on leaflets at the basal part of the diseased plants. Thirty-four bacterial isolates from WT plants were characterized and identified together with 16 strains of Pseudomonas syringae pv. pisi from common bacterial blight of pea. The bacteria were gram-negative rods, having one to six polar flagella. The results of LOPAT tests were + - - - +, showing that they belong to P. syringe. In stab inoculation on stems, the WT isolates produced WT symptoms with water-soaked spots 14 days after inoculation. The 16 P. syringae pv. pisi strains never induced WT symptoms and, on the contrary, caused the typical bacterial blight. WT isolates were not pathogenic on any other plants tested. Phenotypic properties differentiated WT isolates and P. syringae pv. pisi strains into two groups; one consists of WT isolates and P. syringae pv. pisi group A, the other is P. syringae pv. pisi group B. Two distinct fingerprint profiles were identified by repetitive sequence based-polymerase chain reaction. WT isolates and P. syringae pv. pisi group A belonged to the same fingerprint type in rep-PCR, whereas a distinct fingerprint was shown by strains of the P. syringae pv. pisi group B. We concluded that the WT isolates should be included in P. syringae pv. pisi as a distinct strain in symptom expression.

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