Research article Histo-chemical and biochemical analysis reveals association of er1 mediated powdery mildew resistance and redox balance in pea Chinmayee Mohapatra a , Ramesh Chand a, * , Sudhir Navathe a , Sandeep Sharma b a Department of Mycology and Plant Pathology, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh 221007 India b Marine Biotechnology and Ecology Division, CSIR-Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat, India article info Article history: Received 13 December 2015 Received in revised form 18 April 2016 Accepted 18 April 2016 Available online 23 April 2016 Keywords: Powdery mildew er1 gene Antioxidant enzymes Pea abstract Powdery mildew caused by Erysiphe pisi is one of the important diseases responsible for heavy yield losses in pea crop worldwide. The most effective method of controlling the disease is the use of resistant varieties. The resistance to powdery mildew in pea is recessive and governed by a single gene er1. The objective of present study is to investigate if er1 mediated powdery mildew resistance is associated with changes in the redox status of the pea plant. 16 pea genotypes were screened for powdery mildew resistance in field condition for two years and, also, analyzed for the presence/absence of er1 gene. Histochemical analysis with DAB and NBT staining indicates accumulation of reactive oxygen species (ROS) in surrounding area of powdery mildew infection which was higher in susceptible genotypes as compared to resistant genotypes. A biochemical study revealed that the activity of superoxide dismutase (SOD) and catalase, enzymes involved in scavenging ROS, was increased in, both, resistant and suscep- tible genotypes after powdery mildew infection. However, both enzymes level was always higher in resistant than susceptible genotypes throughout time course of infection. Moreover, irrespective of any treatment, the total phenol (TP) and malondialdehyde (MDA) content was significantly high and low in resistant genotypes, respectively. The powdery mildew infection elevated the MDA content but decreased the total phenol in pea genotypes. Statistical analysis showed a strong positive correlation between AUDPC and MDA; however, a negative correlation was observed between AUDPC and SOD, CAT and TP. Heritability of antioxidant was also high. The study identified few novel genotypes resistant to powdery mildew infection that carried the er1 gene and provided further clue that er1 mediated defense response utilizes antioxidant machinery to confer powdery mildew resistance in pea. © 2016 Elsevier Masson SAS. All rights reserved. 1. Introduction Pea (Pisum sativum L.) is one of the important grain legume crop worldwide mainly used for consumption as green vegetables and dry seeds (Katoch et al., 2010). Pea crop is cultivated in 7.3 million hectares with total production 600 metric tons globally (FAOSTAT, 2013). The productivity of pea is affected by many diseases and insect-pests (Kraft and Pfleger, 2001). Among the various diseases affecting pea, powdery mildew, caused by Erysiphe pisi, is of great significance. It affects all the green parts of the plant and cause yield loss 25e50% (Warkentin et al., 1996). This disease adversely affects the biomass and yield of plants mainly by reducing a number of pods per plant, seeds per pod and plant height (Gritton and Ebert, 1975). The disease spreads rapidly during the dry weather when the nights are cooler (Reilling, 1984). The biological cycle of E. pisi includes germination of conidia (asexual spores) or ascospores (sexual spores), a formation of appressorium and haustorium, development of colonies epiphytically on the host epidermis and production of new spores for repeated infection (Pavan et al., 2011). The most efficient and ecologically sound strategy to manage the disease is the use of resistant cultivars. The pea cultivar Xucai 1 has shown high resistance to E. pisi under greenhouse and field conditions (Sun et al., 2015). The resistance to powdery mildew in pea is governed by a single recessive gene ‘er1’ (Harland, 1948; Pierce, 1948). Later, two other genes for resistance named er2 and Er3 (Heringa et al., 1969; Fondevilla et al., 2007) have also been Abbreviations: SOD, Superoxide dismutase; MDA, Malondialdehyde; CAT, Cata- lase; TP, Total phenol; AUDPC, Area Under Disease Progress Curve; DAB, 3,3- diaminobenzidine; NBT, Nitro blue tetrazolium; ROS, Reactive Oxygen Species; EU g 1 FW, enzyme units per gram fresh weight; TCA, Trichloro acetic acid; TBA, Thiobarbituric Acid; hai, hours after inoculation. * Corresponding author. E-mail address: rc_vns@yahoo.co.in (R. Chand). Contents lists available at ScienceDirect Plant Physiology and Biochemistry journal homepage: www.elsevier.com/locate/plaphy http://dx.doi.org/10.1016/j.plaphy.2016.04.035 0981-9428/© 2016 Elsevier Masson SAS. All rights reserved. Plant Physiology and Biochemistry 106 (2016) 54e63