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Systematic-Host Assay of Sugarcane Mosaic Virus. Jack L. Dean, Research Plant Pathologist, Crops Research Division, ARS, USDA, Canal Point, Florida 33438; Phytopathology 61:526-531. Accepted for publication 30 November 1970. DOI: 10.1094/Phyto-61-526.

Sugarcane mosaic virus was quantitatively bioassayed by systemic infection of seedlings of Sorghum bicolor with a degree of accuracy previously considered attainable with plant viruses only by local-lesion assay. Two inocula differing from each other by 10% in viral concentration consistently gave highly significant differences in percentage of test plants infected. Mechanical methods for planting and inoculating permitted handling large numbers of test plants with relatively small effort. The number of plants required was reduced by certain precautions for controlling random variation: (i) the use of sized, disease-free seed; (ii) uniform filling of pots with thoroughly mixed soil; (iii) fumigation of the soil in place in the pots; (iv) uniform depth of planting of the seeds; (v) uniform irrigation of the growing test plants; and (vi) elimination of position effects by growing the test plants in pots arranged in a circle on a rotating table. Data on the number of primary infection sites per systemically infected plant suggest that sometimes the methods for handling large numbers of test plants might profitably be used to extend the range of local-lesion assays. These data also suggest that mass handling techniques could make possible the efficient use of systemic infections for the separation and purification of virus strains, just as single local lesions are commonly used for this purpose.

Additional keywords: Infection sites, local-lesion assay, Sorghum, Saccharum.