Np. Orolaza et al., EVIDENCE OF A HOST-SPECIFIC CHLOROSIS TOXIN FROM PYRENOPHORA-TRITICI-REPENTIS, THE CAUSAL AGENT OF TAN SPOT OF WHEAT, Phytopathology, 85(10), 1995, pp. 1282-1287
Spore germination fluid, cell-free culture filtrate, and intercellular
washing fluid from race 5 of Pyrenophora tritici-repentis contained a
host-specific toxin which elicited extensive chlorosis on Katepwa and
6B662, characteristic of the chlorotic symptom induced by the fungus
on the same wheat genotypes. These three sources of toxin showed equiv
alent host specificity. Other races (including races 1 and 3) which ar
e known to induce chlorosis in different wheat genotypes than does rac
e 5 did not produce a detectable level of a chlorosis toxin, as assess
ed by bioassay, when grown in a still liquid culture or during spore g
ermination. Of the 15 plant species tested, only wheat (genotypes 6B66
2, Katepwa, and Neepawa) and triticale (cv. Banjo) developed distinct
chlorosis when inoculated with race 5 or infiltrated with its spore ge
rmination fluid or partially purified culture filtrate. F-2 progenies
from a cross between race 5-susceptible and race 5-resistant wheat gen
otypes were evaluated. Susceptibility of the seedlings to race 5 and t
heir sensitivity to its toxin cosegregated. A ratio of 1:3 (resistant/
susceptible) was observed, suggesting the involvement of a single, dom
inant locus controlling the reaction to the fungus and the toxin. The
chlorosis toxin appeared to be a pathogenicity factor and was designat
ed as Ptrchlorosis toxin.