Vegetative Compatibility Groups and Aggressiveness of North American Isolates of Colletotrichum coccodes, the Causal Agent of Potato Black Dot.

The vegetative compatibility of 123 isolates of Colletotrichum coccodes from North America (United States and Canada) originating from potato, tomato, pepper, and mint was tested using nitrate-nonutilizing (nit) mutants. The North American isolates did not anastomose with previously selected European/Israeli vegetative compatibility group (VCG) testers; therefore, eight isolates were selected as VCG testers for the North American population. The 123 isolates distributed to seven VCGs at 1.6, 1.6, 4.0, 8.1, 13.8, 19.5, and 36.6%, with 14.6% of the isolates not assigned to any of the seven VCGs. Among the North American (NA)-VCGs, the average frequency of the nit1/nit3 nit mutants was lower (P < 0.05) for isolates belonging to NA-VCG1 than for isolates belonging to the NA-VCGs 2, 3, and 5. In contrast, the frequency of NitM nit mutants did not vary (P > 0.05) among the NA-VCGs and was collectively 5.14%. The results also indicated significant (P < 0.05) differences among NA-VCGs and European/Israeli (EU/I)-VCGs regarding the frequency of nit mutants. The aggressiveness trials of the North American isolates to potato indicated that plants infected with isolates belonging to NA-VCG2 and NA-VCG5 had more (P < 0.05) sclerotia on the roots and crowns than plants infected with isolates belonging to NA-VCGs 1 and 3. The plants infected with isolates belonging to NA-VCG2 had sclerotia formed higher (P < 0.05) up the stem than the plants infected with isolates belonging to NA-VCGs 1, 3, or 5. The plants infected with isolates assigned to NA-VCG2 had more (P < 0.05) infected progeny tubers than the plants infected with isolates belonging to NA-VCGs 1, 3, or 5; and the plants infected with isolates belonging to NA-VCGs 1, 2, and 5 yielded fewer (P < 0.05) potato tubers than the noninoculated control plants. A naming system for the population of C. coccodes based on the continent source of the population, the VCG number, and the isolate's code was suggested.

Colonization of Potato Plants after Aerial Infection by Colletotrichum coccodes, Causal Agent of Potato Black Dot.

Colonization of potato plants by Colletotrichum coccodes after artificial inoculation of stems was modeled in relation to the severity of chlorosis and necrosis on foliage using logistic regression. C. coccodes internally colonized the stems up to 24 cm above the inoculation court (mean of 11.3 ± 7.7 cm and 14.1 ± 9.3 cm in 2003 and 2004, respectively), and completely colonized the stem below the inoculation court including the roots (mean of 13.2 ± 3.1 cm and 12 ± 2.3 cm in 2003 and 2004, respectively). C. coccodes grew significantly faster from the inoculation court toward the roots, stolons, and tubers than toward the plant apex. Internal stem colonization was restricted before senescence but rapidly increased as the plants started to senescence, suggesting that physiological events associated with plant senescence activated fungal growth and plant colonization. The results showed no relationship between C. coccodes growth and plant colonization and the development of chlorosis and necrosis severity of leaves. The severity of chlorosis and necrosis on foliage in this study was the outcome of natural plant senescence, and was not caused by the fungal colonization. Therefore, chlorosis and necrosis severity is an inaccurate tool to diagnose infection in potato by C. coccodes and does not indicate the presence or amount of C. coccodes in potato plants. Disease assessment for C. coccodes in potato plants should not rely on severity of chlorosis and necrosis. Black dot assessment should be carried out by isolation and quantification of the fungus from stem and root tissues or by polymerase chain reaction techniques before plant senescence.

Effect of Seed-Tuber Generation, Soilborne Inoculum, and Azoxystrobin Application on Development of Potato Black Dot Caused by Colletotrichum coccodes.

The effect of azoxystrobin on potato black dot and the role of seed- and soilborne inocula of Colletotrichum coccodes in the development of black dot were evaluated in the field using two potato seed generations (generation 1 and 3) of the susceptible cvs. Norkotah Russet and Russet Burbank over 3 years (2002 to 2004). Plants of Norkotah Russet and Russet Burbank treated with azoxystrobin had 13 and 23% higher yields, respectively, than nontreated plants in 2003. Disease severity on both cultivars was reduced 19 to 81%, and 22 to 81% on above- and belowground stem sections, respectively, when plants were treated with azoxystrobin. Plants of both cultivars that were treated with azoxystrobin had 9 to 26% less infected progeny tubers than the nontreated plants. These results indicated the efficacy of azoxystrobin to reduce black dot severity on both stems and progeny tubers. The roles of seed- and soilborne inocula in disease development were evaluated in 2003 and 2004 using generation 1 and 3 seed tubers. The incidence of C. coccodes in generation 1 mother tubers of Norkotah Russet and Russet Burbank were 2 and 16% in 2003, respectively, and 0 and 30% in 2004, respectively. The incidence of C. coccodes in generation 3 mother tubers of Norkotah Russet and Russet Burbank were 14 and 49% in 2003, respectively, and 12 and 38% in 2004, respectively. Generation 1 plants of Norkotah Russet had 36 and 13% greater yield than generation 3 plants in 2003 and 2004, respectively. In 2004, generation 1 plants of Norkotah Russet and Russet Burbank had 26 and 15% greater disease severity, respectively, on belowground stem than generation 3 plants. Generation 1 plants of Norkotah Russet had 7.5 and 11% more infected progeny tubers in 2003 and 2004, respectively, than generation 3. Significant differences for yield reduction and incidence of infected progeny tubers between the two seed generations were not recorded for Russet Burbank, suggesting that the effect of inoculum source of C. coccodes on black dot severity may be cultivar specific.

Vegetative Compatibility Groups in Colletotrichum coccodes, the Causal Agent of Black Dot on Potato.

ABSTRACT Black dot of potato, caused by Colletotrichum coccodes, is a disease of growing economic importance, but the degree of genetic diversity and pathogenic differentiation among isolates is unknown. Using nitrate auxotrophic (Nit) mutants, we characterized vegetative compatibility groups (VCG) diversity for C. coccodes for 110 isolates originating from Israel, The Netherlands, and France. We recovered frequencies of nit1 and NitM mutant classes at 38.5 and 7.2%, respectively, and selected 12 isolates as tester isolates. Using these testers, we defined four multimember VCGs at 7.3, 35.5, 20.0, and 10.0% frequency in this sample. Thirty isolates (27.3% of all tested isolates) could not be assigned to any of the major groups, and showed only self-compatibility. The frequency of recovery of Nit mutant sectors was highest in isolates from VCG4, with 50.9 and 13.6% recovery for nit1 and NitM, respectively. However, we did not detect differences in the frequency of mutant classes among the three countries of origin. In pathogenicity tests, isolates from VCG3 were the most aggressive to potato, as expressed by high stem colonization levels and sclerotia density on root and crown. These results suggest that there is significant VCG diversity in this species and that this VCG diversity may be correlated with pathogenic characteristics or specialization.

Inherited inverted duplication of X chromosome in a male: report of a patient and review of the literature.

Nineteen cases of duplication of segments of the long arm of chromosome X have been published in 13 males and in 6 females. We report an additional case of a male with growth and mental retardation, growth hormone deficiency, compensated primary hypothyroidism, distinctive anomalies of the face, hypoplastic genitalia, and hypotonia in whom inverted duplication of a segment in the long arm of X chromosome was diagnosed, 46,Y, dup (X)(q21.2q13.3), and mosaicism was demonstrated in his mother's X chromosome. The rearranged segment was diagnosed utilizing high resolution G-band technique and FISH studies, using chromosome X total chromosome probe and DNA XIST probe. This appears to be the first report of a patient with duplication of Xq and hypothyroidism.