Submitted to: Sugar Cane
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/1997
Publication Date: N/A
Interpretive Summary: Sugarcane leaf scald has increased in Florida and its effect on yield in commercial fields is not known. Visually determining the frequency of leaf scald at harvest is difficult, if not impossible, because of the large amount of plant material present and some infected plants have no symptoms. Serological and isolation methods were used to estimate leaf scald frequency in commercial sugarcane fields. These techniques when used on the same stalks, identified stalks showing disease symptoms (serological positive) and stalks that were infected showing no external symptoms (serological negative but positive by isolation). Healthy stalks were negative for both tests. Symptomatic stalks ranged from 1.1 to 12.2% in ten commercial sugarcane fields. The frequency of asymptomatic stalks ranged from zero to 16.1%. The frequency of infected stalks (detected by both methods) ranged from 1.1 to 27.2%. Leaf scald reduced most yield components of symptomatic stalks. Estimated yield loss was 2.8% based on the percentage of symptomatic stalks in fields surveyed. These techniques will be useful in estimating leaf scald frequency and losses in sugarcane fields.
Technical Abstract: Serological techniques were evaluated to detect leaf scald symptomatic stalks, since visual observation at harvest is difficult because of pre-harvest burning and tangled stalks. Enzyme-linked immunosorbent assay (ELISA) and dot immunobinding assays (DIA) gave positive results in 99% of the 116 visually symptomatic stalks and 1.4% of the asymptomatic stalks examined. Isolation on selective agar also detected the leaf scald pathogen, Xanthomonas albilineans, in all the serological positive stalks as well as in 16% of the asymptomatic stalks that were negative serologically. Because the serological assay had a high rate of detecting symptomatic stalks and had a low rate of detecting asymptomatic stalks, it was used to estimate symptomatic stalks in ten commercial sugarcane fields. Stalks that were negative serologically using DIA and ELISA but positive using an isolation assay were regarded as infected asymptomatic stalks. The incidence of serological detection of X. albilineans ranged from 1.1 to 12.2% for the ten commercial sugarcane fields surveyed. For the same fields, X. albilineans detection by isolation but not by serology ranged from none to 16.1%. Leaf scald significantly reduced most yield components of sugarcane. Stalk weight was an exception.