ORIGINAL ARTICLE Defence-Related Enzymes in Soybean Resistance to Target Spot Alessandro A. Fortunato, Daniel Debona, Arthur M. A. Bernardeli and Fabr  ıcio A. Rodrigues Departamento de Fitopatologia, Laborat orio da Interac ß~ ao Planta-Pat ogeno, Universidade Federal de Vic ßosa, Vic ßosa, Cep 36570-900, Brazil Keywords Corynespora cassiicola, Glycine max, lignin, mechanisms of host defence Correspondence F. A. Rodrigues, Universidade Federal de Vic ßosa, Vic ßosa, Brazil. E-mail: fabricio@ufv.br Received: October 27, 2014; accepted: December 15, 2014. doi: 10.1111/jph.12370 Abstract Target spot, caused by the fungus Corynespora cassiicola, has become a serious foliar disease in soybean production in the Brazilian Cerrado. Information in the literature regarding the biochemical defence responses of soybean to C. cassiicola infection is rare. Therefore, the objective of this study was to determine the biochemical features associated with soybean resistance to target spot. The activities of chitinases (CHI), b-1-3- glucanases (GLU), phenylalanine ammonia-lyases (PAL), peroxidases (POX), polyphenol oxidases (PPO) and lipoxygenases (LOX), as well as the concentrations of total soluble phenolics (TSP) and lignin-thioglycolic acid (LTGA) derivatives, were determined in soybean leaves from both a resistant (FUNDACEP 59) and a susceptible (TMG 132) cultivar. The target spot severity, number of lesions per cm 2 of leaflet and area under the dis- ease progress curve were significantly lower for plants from cv. FUNDA- CEP 59 compared to plants from cv. TMG 132. The GLU, CHI, PAL, POX and PPO activities and the concentration of LTGA derivatives increased significantly, whereas LOX activity decreased significantly on the leaves infected by C. cassiicola. Inoculated plants from cv. FUNDACEP 59 showed a higher PPO activity and concentrations of TSP and LTGA derivatives at 4 and 6 days after inoculation compared to plants from cv. TMG 132. In conclusion, the results of this study demonstrated that the defence-related enzyme activities increased upon C. cassiicola infection, regardless of the basal level of resistance of the cultivar studied. The increases in PPO activity and concentrations of TSP and LTGA derivatives, but lower LOX activity, at early stages of C. cassiicola infection were highly associated with soybean resistance to target spot. Introduction Soybean [Glycine max (L.) Merrill] is considered to be one of the most important crops grown in Brazil and other countries worldwide (Godoy et al. 2012). However, the occurrence of many foliar diseases on soybean has caused significant yield losses (Yorinori 1997; Sinclair 1999). Target spot, caused by the fun- gus Corynespora cassiicola (Berk & MA Curtis) CT Wei., has become an important foliar disease affecting soybean production in Brazil. A symptom of target spot on leaves is the occurrence of small lesions with a very well developed yellow halo, which can reach two inches in diameter, become circular and brownish and may coalesce as they expand (Sinclair 1999; Almeida et al. 2005). When susceptible soybean cultivars are grown under favourable climatic condi- tions (e.g. intense rainfall and high temperatures), premature defoliation can occur (Godoy et al. 2012; Teramoto et al. 2013). The fungus is also able to cause rot in roots and pods and lesions on stems, and it can eventually infect the seeds (Sinclair 1999). Seed treat- ment with fungicides, foliar spray of fungicides and crop rotation are the most used control strategies for target spot management (Almeida et al. 2005). How- ever, due to the absence of resistant cultivars and the occurrence of C. cassiicola isolates resistant to fungi- cides, epidemics of target spot have been frequent in many soybean-growing regions in Brazil (Godoy et al. 2012; Teramoto et al. 2013). As a foliar J Phytopathol 163 (2015) 731–742 Ó 2015 Blackwell Verlag GmbH 731 J Phytopathol