28.
One hundred and sixteen isolates of
Fusarium oxysporum f. sp.
lactucae obtained from 85 fields in three crisphead lettuce-producing areas in Nagano Prefecture, Japan were typed for races using
differential cultivars Patriot, Banchu Red Fire and Costa Rica No. 4. They were also grouped into vegetative compatibility
groups (VCGs) using complementation tests with nitrate non-utilizing
(nit) mutants. Two California strains reported as
F. oxysporum f. sp.
lactucum, a type culture of
F. oxysporum f. sp.
lactucae, and 28 avirulent isolates of
F. oxysporum obtained from crisphead lettuce were included for comparison. Among Nagano isolates, 66 isolates were identified as race 1,
and 50 as race 2. Race 1 strains derived from Shiojiri and Komoro cities and race 2 from Kawakami village and Komoro city.
All isolates of race 2 were biotin auxotrophs, and the race could be distinguished based on its requirement for biotin on
minimal nitrate agar medium (MM). Pathogenic isolates were classified into two VCGs and three heterokaryon self-incompatible
isolates. Strong correlations were found between race and VCG. All the race 1 strains were assigned to VCG 1 except self-incompatible
isolates, and all the race 2 strains to VCG 2. The 28 avirulent isolates of
F. oxysporum were incompatible with VCG 1 and VCG 2. California strains was vegetatively compatible with VCG 1, and they were assigned
to race 1. Based on vegetative compatibility, these two races of
F. oxysporum f. sp.
lactucae may be genetically distinct, and
F. oxysporum f. sp.
lactucae race 1 is identical to
F. oxysporum f. sp.
lactucum.
Received 7 May 2002/ Accepted in revised form 6 September 2002
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