Biochemical and histopathological alterations due to root-knot nematode, Meloidogyne graminicola in rice (Oryza sativa L.) and varietal reactions

Abstract

An experiment entitled “Biochemical and histopathological alterations due to root- knot nematode, Meloidogyne graminicola in rice (Oryza sativa L.) and varietal reactions” was undertaken at Department of Agricultural Entomology, College of Agriculture, Vellayani, during 2013-14. A progressive increase in phenol content, defense enzymes viz. Peroxidase (PO), Polyphenol Oxidase (PPO), Phenylalanine Ammonia Lyase (PAL) from both leaf and root after 45 days of nematode inoculation were observed with increase in inoculum levels. The chlorophyll a and b, NPK content and micronutrients viz. Fe, Cu, Zn and Mn were decreased with increase in nematode population. The plants inoculated with 10,000 J2 showed low pH (5.69) compared to the uninoculated plant and was significantly different from all other treatments. The starch, protein and total sugar content decreased 41.44, 41.89 and 44.95 per cent respectively in plants inoculated with 10,000 J2 compared to uninoculated plants. A progressive decrease in plant growth and yield parameters were observed with increase in population levels of nematode. The maximum reduction in plant height, fresh weight of plant, dry weight of root and dry weight of shoot and the yield parameters like thousand seed weight and number of seeds per panicle were observed in plants inoculated with 10,000 J2. Histochemical studies revealed that an accumulation of polysaccharides, proteins and nucleic acid in epidermal, cortical and stelar region of root progressively increased with increase in population density of nematode. Giant cells were formed near the xylem and phloem cells. The xylem and phloem vessels were disorganized. In studying the varietal reaction of ten popular rice varieties of Kerala against M. graminicola, all the varieties were suceptible to the nematode. Minimum number of galls (51.8) and egg mass (64.60) per plant was observed in the variety Uma and was on par with Pavizham. On the basis of egg mass index, all other varieties were highly susceptible except Uma. The PO and PPO activity of Uma, Karthika, Pavizham and Bhadra were higher than that of TN1 (Suceptible check). In Uma, the nematode population in soil and root was minimum and on par with Karthika and the reproduction rate also minimum in Uma. Based on the results of the study, M. graminicola can be considered as a potential threat to the cultivation of rice. Uma showed better performance against root knot nematode than all other varieties.