Abstract
Brown leaf spot disease of rice is a dominant lethal disease, caused by the fungus Bipolaris oryzae. The pathogen is an obligate parasite and causes qualitative and quantitative damage to rice crop. The objective of the present study was to investigate what extent the defense related biochemical compounds reflect the distinct categories of resistance phenotypes in rice against brown spot disease. This was done by determining the concentration of Catalase (CAT), Phenylalanine ammonia-lyase (PAL), Polyphenol oxidase (PPO), Peroxidase (POD), and β-1,3-Glucanase enzymes in resistant, moderately resistant and susceptible rice genotypes. The disease resistant phenotypes in rice line (PARC-7) reflect the higher accumulation of CAT, PAL, PPO, POD, and β-1,3-Glucanase. The pattern of enzyme accumulation was similar in all resistant genotypes. The rice genotypes with moderately resistant phenotypes showed significant difference with respect to the concentration of biochemical defense-related compounds. The difference in accumulation of defense related enzymes reflected the level of disease severity (% leaf area covered) on resistant and moderately resistant genotypes. The susceptible rice genotypes showed the minimum concentration of these enzymes, with the lowest concentrations found in the rice variety Bas-2000 (80% Disease Index). The differential defense response in resistant and susceptible genotypes suggests that these enzymes can be used as biochemical markers for early detection of disease resistant genotypes. The study of enzyme accumulation at different time points and at different levels of disease severity helps to understand the resistance mechanisms against brown spot disease in rice.
Highlights
Rice (Oryza sativa) is a major food crop of Pakistan and staple food after wheat, and the third largest crop in terms of area sown
Rice leaves infected by the brown spot disease exhibited lesions appeared on leaves that were originally dark brown in color ranging to purple-brown, with a light brown to grayish center and margins on the leaves were reddish-brown (Figure 1a, Supplementary Figure 2)
Septate mycelia of brown spot pathogen were observed on PDA media (Figure 1b)
Summary
Rice (Oryza sativa) is a major food crop of Pakistan and staple food after wheat, and the third largest crop in terms of area sown (https://reliefweb.int/sites/reliefweb.int/files/resources/Pakistan_ Food_Security_Bulletin_September_2016.pdf). Fungal and bacterial diseases play a vital role in damaging health of rice crops and lessening rice production. In Pakistan, reports reveal that there is a loss of $5 billion due to diseases of rice (Asghar et al, 2007). Biochemical Profiling of Resistant Phenotypes important pathogens of rice are Pyricularia oryzae, Helminthosporium oryzae, and Xanthomonas oryzae, which causes blast, brown spot, and bacterial blight (Singh et al, 2013). Brown leaf spot disease caused by Bipolaris oryzae is one of the distinctive and most damaging disease of rice in the world, because of the extensive distribution of numerous physiological races (Arshad et al, 2008). Brown spot disease is linked with many important epidemics in the world with the most destructive occurring in 1942 that resulted in the Great Bengal Famine. Weeds that serve as alternative hosts and soils are important as sources of inoculum for this pathogen survival (Biswas et al, 2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
