AbstractA previously undescribed species of Helminthosporium was isolated from leaves of P.R. 980 and P.R. 1059 showing lesions resembling those of brown stripe. The conidia of the new Helminthosporium isolate resemble those of H. rostratum but the long, constricted, cylindrical rostrate conidia, characteristic of this fungus, are absent. The conidia of H. holmii, another allied species, also were examined. The conidia of the new species are smaller in diameter than those of H. holmii. In view of the variations in size and shape and the absence of the characteristic rostrate conidia, the new fungus is given the name Helminthosporium portoricensis n. sp. Results of the cultural studies indicated that the newly described species has the same optimum temperature and pH range as that of H. rostratum and H. holmii. This new isolate grew comparatively faster, however, than the other two species on potato dextrose agar. Among the varieties tested, P.R. 1207, P.R. 1028, and P.R. 1048 seemed to be particularly resistant to portoricensis.
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