Differential Responses of Soybean Cultivars to Cercospora sojina Isolates, the Causal Agent of Frogeye Leaf Spot in Korea

Abstract

During the summer of 2005, specimens of soybean cultivars (Daepung, Daewon, Hwanggeum and Taegwang) showing frogeye leaf spot (FLS) were obtained from various areas in Korea. Eight isolates identified as Cercospora sojina were inoculated on the adaxial leaf surfaces of 63 Korean soybean cultivars; the disease responses to each isolate were evaluated 14 days and 21 days after inoculation. Based on the disease responses (resistant or susceptible) of the cultivars by the isolates, a set of cultivars (Anpeong, Bogwang, Cheongdu No. 1, Cheongja No. 3, Dachae, Daemang, Jangwon, Namhae, Sowon, Taegwang) were selected and inoculated with seven isolates for further testing pathogenic variance. Interestingly, 6 out of 7 tested C. sojina isolates revealed differential ability in infecting different soybean cultivars. This result may indicate the possibility of new race occurrence or pathogenic variation; this also presents evidence for prevalent FLS occurrence during humid and hot weather in Korea.

Silicon‐Induced Changes in the Antioxidant System Reduce Soybean Resistance to Frogeye Leaf Spot

“…The activities of most of the antioxidant enzymes in the +Si-inoculated plants were enhanced to counteract the increased ROS (mainly O 2 À ) concentration via a mechanism that is most likely mediated by toxins that are released by C. sojina. Although the toxin cercosporin, typically secreted by Cercospora spp., is unknown to be produced by C. sojina (Daub et al 2013), the yellowing surrounding the lesions is considered a consequence from other C. sojina-synthesized toxins (Kim et al 2011). This fact is supported by the positive correlation between both O 2 À concentration and FLSS and O 2 À concentration and FSC found in this study.…”

“…Although some studies have found that the activities of SOD and POX in soybean leaves (Shen et al 2010) and of GPX in cucumber leaves (Zhu et al 2004) increased in the presence of Si, the results of the present study are somewhat unexpected given that Si is believed to affect the plant metabolism and physiology only under stressed conditions (Epstein 1994). Nevertheless, because C. sojina is probably benefited from ROS that are generated in the necrotic tissue as a consequence of toxins secretion (Kim et al 2011), it is tempting to suggest that the Simediated lower robustness of the antioxidant system could explain why Si exacerbated soybean susceptibility to FLS.…”

“…sojina is probably benefited from ROS that are generated in the necrotic tissue as a consequence of toxins secretion (Kim et al. ), it is tempting to suggest that the Si‐mediated lower robustness of the antioxidant system could explain why Si exacerbated soybean susceptibility to FLS.…”

“…), the yellowing surrounding the lesions is considered a consequence from other C. sojina ‐synthesized toxins (Kim et al. ). This fact is supported by the positive correlation between both O 2 − concentration and FLSS and O 2 − concentration and FSC found in this study.…”

“…Because FLS has been controlled mainly by using cultivars with race-specific resistance to C. sojina (Missaoui et al 2007), novel epidemics may occur due to the high genetic variability of the fungus, especially in the context of emerging resistance to strobilurin fungicides (Kim et al 2011(Kim et al , 2013. Therefore, the potential indiscriminate use of Si to control other soybean diseases such as Asian rust may be an additional factor that could increase FLS importance.…”