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Comparison of Inoculation with Maize Dwarf Mosaic Virus on the Abaxial and Adaxial Leaf Surfaces in Corn. Eugen Rosenkranz, Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Mississippi State University, Mississippi State 39762; Gene E. Scott, Research agronomist, ARS, USDA, and professor, Department of Agronomy, Mississippi State University, Mississippi State 39762. Phytopathology 77:1243-1246. Accepted for publication 27 February 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1987. DOI: 10.1094/Phyto-77-1243.

The effect of inoculating abaxial (lower) versus adaxial (upper) leaf surfaces of corn with maize dwarf mosaic virus (MDMV) was investigated in the field for 2 yr to determine which surface was more susceptible to infection. In both years, plants of three corn hybrids (Ab28A × T226, T226 × T232, and Mo12 × Tx601) had significantly higher disease incidence when inoculated with MDMV strain A (MDMV-A) on the lower than on the upper leaf surfaces. Of 72 comparisons (three hybrids × four replications × six evaluation days) made during 1984, 67 had a higher percentage of diseased plants for inoculation on the lower than upper leaf surfaces. In 1985, 82 of 84 comparisons (three hybrids × four replications × seven evaluation days) had a higher disease incidence for lower-than for upper-surface inoculation. The range in the increase of disease incidence resulting from inoculation of the lower over the upper leaf surfaces amounted to 15–140% in 1984 and 18–130% in 1985. The time of day when inoculation was made, however, affected the magnitude of the difference in disease incidence between the two inoculation sites, being smallest when inoculation was performed at midday. In fact, there was also no statistical difference in disease incidence between plants inoculated, on the same day, on the lower leaf surfaces at midday and plants inoculated on the upper leaf surfaces at sunset. It is suggested that inoculation of the lower surfaces of corn leaves with MDMV-A in the field leads to increased disease incidence because reduced light intensity and enhanced relative humidity cause a high turgor pressure in the abaxial epidermal cells facilitating their wounding for virus entry.