Horizontal and vertical droplet dispersion mimicking soybean - Septoria glycines pathosystem
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The horizontal and vertical dispersion of droplets was assessed aiming at studying influence of their numbers and distances on spread of spores of Septoria glycines Hemmi simulating its pathosystem with soybean [Glycine max (L.) Merrill] plants. Two drop diameters (1.8 mm and 3.4 mm) were assessed under two soil conditions: bare soil and soil covered with wheat straw. Results showed that larger drops had greater effect on producing droplets than smaller drops. The number of horizontally dispersed droplets increased with increase on number of drops assessed (5, 10, or 20 drops) on both diameters used; as well as for both soil conditions assessed. The number of droplets vertically dispersed was assessed using only 5 and 10 drops, and increased as drop size increased; mainly under bare soil condition. Twenty drops were also assessed, but such water amount drenched the soil and did not allow recording vertical dispersal of droplets. The epidemic caused by splashes of droplets on bare soil caused infection on a larger number of plants than the epidemic caused by splashes on soil covered with wheat straw. These findings confirm why this is one of the first soybean disease to occur in the field and show in vivo the upward dislocation of S. glycines spores for the first time. Such upward movement was based on the following infection levels: 1 = no infection; 2 = up to 15% of the leaf infected; 3 = up to 30% of leaf infected; 4 = up to 45% of leaf infected; and 5 = more than 60% of the leaf infected.
KeywordsRain drops Epidemiology Brown spot Spore displacement Simulation
The authors are grateful to Dr. Carlos Caio Machado, Dr. Regina M.V.B.C. Leite and Dr. Norman Neumaier for their critical review of this manuscript, and to Luiz C. Benato and Nilson V. Souza for their valuable help. The authors also would like to thank the anonymous reviewers for their help.
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