Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 19, 2010
Publication Date: July 18, 2010
Citation: Li, S., Hartman, G.L., Boykin, D.L. 2010. Agressiveness of Phomopsis longicolla and other Phomopsis species on soybean. Plant Disease. 94:1035-1040. Interpretive Summary: Phomopsis seed decay (PSD) of soybean is a major cause of poor quality of soybean seeds. The disease is caused primarily by a fungus (mold). The use of resistant cultivars is the most effective method for controlling PSD. Selection of aggressive (causing severe disease symptoms) fungal isolates is important to evaluate resistance in soybean varieties. Differences among 48 fungal isolates were found based on measurements of disease levels in greenhouse experiments. Soybean isolate PL16 from Mississippi caused the shortest shoot length while the velvetleaf isolate P9 from Illinois caused the greatest shoot lesion length. These aggressive isolates can be used to identify soybean breeding lines with PSD resistance, thus improving soybean production where this disease occurs. Since weeds could harbor aggressive pathogen isolates for PSD, field management practices with proper weed control strategies could be beneficial for soybean production in regard to occurrence of PSD.
Technical Abstract: Phomopsis seed decay of soybean is a major cause of poor quality of soybean seeds. The disease is caused primarily by the fungal pathogen, Phomopsis longicolla. In this study, aggressiveness of isolates of P. longicolla from soybean and other Phomopsis spp. from other hosts were compared by inoculating 2-week old soybean plants of cv. Williams 82. There were significant (P = 0.0001) differences among isolates based on stem length and stem lesion length. Soybean isolate of P. longicolla PL16 from Mississippi caused the lowest stem length while the non-soybean isolate of P. longicolla P9 from Illinois caused the greatest stem lesion length. The type isolate of P. longicolla PL31 (Fau 600) was one of the three most aggressive isolates among all 48 isolates tested. The velvetleaf isolate P9 from Illinois was the most aggressive among 13 isolates (11 Phomopsis spp. and two P. longicolla isolates) from non-soybean hosts, and caused the shortest stem length and the greatest stem lesion length. There was a significantly (P = 0.0001) negative correlation between the stem length and stem lesion length. This study provided the first evaluation of aggressiveness of P. longicolla isolates from different geographic origins and the first demonstration that Phomopsis spp. isolated from cantaloupe, eggplant, and watermelon infected soybean. Knowledge about the variability of the pathogen is important for selection of isolates for breeding for broad-based resistant soybean lines to Phomopsis seed decay.