VIEW ARTICLE

Biochemistry and Cell Biology

Characterization of Sugarcane Response to Bipolaris sacchari: Inoculations and Host-Specific HS-Toxin. Brian L. Bournival, Cellular and Molecular Biology Research Unit, Experiment Station, Hawaiian Sugar Planters’ Association, 99-193 Aiea Heights Dr., Aiea, HI 96701; Harold S. Ginoza, Susan Schenck, and Paul H. Moore. Cellular and Molecular Biology Research Unit, Experiment Station, Hawaiian Sugar Planters’ Association, 99-193 Aiea Heights Dr., Aiea, HI 96701. Phytopathology 84:672-676. Accepted for publication 21 April 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-672.

Twenty-seven sugarcane clones inoculated with Bipolaris sacchari, causal agent of eyespot disease, were classified as susceptible or resistant based on the presence or absence of distinct chlorotic halos surrounding lesions on leaves. Under the inoculation conditions used in this study, all lesions on resistant plants were smaller than 3 mm; the proportion of lesions larger than 3 mm on susceptible clones ranged from 0.2 to 82.2%. The total number of lesions was not related to resistance or susceptibility. All clones classified as resistant to B. sacchari were insensitive to a host-specific toxin (HS-toxin) produced by the pathogen, whereas all susceptible plants produced a water-soaked streak when 1 µl of partially purified HS-toxin was placed in a hole punched in a leaf segment. These results indicated that sensitivity to HS-toxin was an important factor in determining whether the pathogen could cause disease symptoms on the plant. Measurement of toxin-induced electrolyte leakage was not as reliable for differentiating between resistant and susceptible clones. In most susceptible individuals, the degree of disease severity was correlated with the level of sensitivity to HS-toxin; however, there were three clear exceptions, suggesting that in some clones, other factors besides sensitivity to HS-toxin might be involved in determining the extent of symptom expression.