The effect of inoculum density on uredospore germination and infection of corn by Puccinia polysora, the cause of Southern corn rust
Phytopathology 71(7): 769
Uredospores of Puccinia paysora Underw. were deposited by gravitational settling on the upper surface of 2 × 2-cm leaf pieces of field corn (Pioneer 3369A), which were immediately given a dark 16-hr dew period at 25 C and then were floated on 21/1 kinetic in sterile tap water at 27 C. At spore densities of 530, 3,800, 11,200, and 16,000/cm2, germination percentages on leaves were 51, 43, 7, and 4 (respectively) and pustules/cm2 were 23, 57, 82, and 65 (respectively). Single spore inoculations (one spore/leaf piece) resulted in 13-19 pustules/100 inoculations. Appressorium and substomatal vesicle formation, calculated as percentages of germinated spores, did not differ significantly at the various inoculum densities. These data indicate that inhibition of germination is the primary factor that reduces infection efficiency of inoculum at higher densities.