Heterokaryon Incompatibility and Heterozygous Diploid Production in Tomato Wilt Isolates of Verticillium dahliae

Abstract

Auxotrophs derived by UV or N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis from three North American, three European and four Australian tomato wilt isolates of Verticillium dahliae were used to investigate heterokaryon compatibility. Ninety 'crosses' involving race-1 and race-2 isolates were attempted using mixed conidial suspensions and a 'hanging drop' technique. Crosses between North American and Australian isolates failed to produce heterokaryons over a 20 d period but within each of these two groups of isolates (with one exception) the frequency of heterokaryon formation was 100%. In crosses involving the three European isolates the frequency of heterokaryon formation varied from 0 to 100%. Two of the European isolates produced heterokaryons both with North American and with Australian isolates. Prototrophic diploid conidia were recovered from 13 of the 30 crosses that produced heterokaryons. The rate of diploid production was greatest in crosses showing 100% compatibility but rare diploids were recovered from two crosses which had produced no observable heterokaryotic growth on minimal medium. The formation of heterozygous diploids between race-1 and race-2 isolates of V. dahliae indicates the potential for the genetic analysis of pathogenicity through the parasexual cycle.

Assessment of vegetative compatibility of race-2 tomato wilt isolates of Verticillium dahliae in Japan

“…They reported that crossing between North American isolates and Australian isolates failed to produce heterokaryons, but the isolates were fully heterokaryon-compatible within each group, whereas European isolates showed variable compatibility with both the North American and Australian isolates. O'Garro and Clarkson (1988b) pointed out the homogeneity in the North American and Australian isolates and stated that race designation did not appear to affect compatibility. Results of vegetative compatibility among Japanese isolates of V. dahliae race-1 and race-2 also suggested the homogeneity of the Japanese isolates.…”

“…O'Garro and Clarkson (1988b) studied the extent of heterokaryon incompatibility between V. dahliae race-1 and race-2 isolates from different geographical origins. They reported that crossing between North American isolates and Australian isolates failed to produce heterokaryons, but the isolates were fully heterokaryon-compatible within each group, whereas European isolates showed variable compatibility with both the North American and Australian isolates.…”

“…The origin of V. dahliae race-2 was examined by use of auxotrophic mutants and it was shown that each V. dahliae race-2 isolate was complemented only by isolates from the same geographical location (O'Garro and Clarkson, 1988b). O'Garro and Clarkson (1988b) supposed that each V. dahliae race-2 isolate coincidentally emerged from the local population of V. dahliae race-1.…”

“…O'Garro and Clarkson (1988b) supposed that each V. dahliae race-2 isolate coincidentally emerged from the local population of V. dahliae race-1. Verticilliurn dahliae was classified into four VC groups using nitrate nonutilizing (nit) mutants Rowe, 1990, 1991).…”

Difficulty to establish vegetative compatibility of Japanese isolates of Verticillium dahliae Kleb. using melanin-synthesis deficient mutants.

“…Heterokaryon compatibility groups suggested the existence of diverse genetic populations in imperfect fungi (6). It was examined by using complementary auxotrophic mutants (23,31) or color mutants (28). V. dahliae formed black microscletrotia where melanin granules concentrated in cell wall layers (36).…”