Chemical and Biochemical Responses of Rice Genotypes against Rice Leaf Folder, Cnaphalocrocis medinalis Guenee
Abstract
Investigations on impact of chemical constitution of leaves on per cent damaged leaves and number of larvae showed the highly significant positive correlation with nitrogen (r=0.8899 and 0.8768) and phosphorus (r=0.7623 and 0.7756, respectively) content. However, per cent damaged leaves and number of larvae showed non-significant positive correlation with magnesium (r=0.2699 and 0.1999), sulphur (r=0.1523 and 0.0310), iron (r=0.1322 and 0.0338,) and zinc (r=0.3023 and 0.3668, respectively) contents. Whereas, per cent damaged leaves and number of larvae showed the highly significant negative correlation with potassium content (r=-0.8240 and -0.7937), non-significant negative correlation with calcium (r=-0.3229 and -0.3243), manganese (r=-0.1946 and -0.2801) and copper (r=-0.1248 and -0.0751, respectively) contents. The results on biochemical constitution of leaves of test genotypes revealed that per cent damaged leaves and number of larvae showed the highly significant positive correlation with crude protein (r=0.9025 and 0.8838), total chlorophyll (r=0.8749 and 0.8234), total soluble sugar (r=0.8338 and 0.8163) and moisture (r=0.5263 and 0.5534, respectively) content.
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Introduction
Rice (Oryza sativa L.) belongs to the family Poaceae and is one of the most important cereal crops worldwide. It serves as a staple food for more than two billion people, particularly in developing countries, where it plays a vital role in food security, nutrition, employment and rural livelihoods (Appala et al., 2018). Rice is grown over 120 million hectares to produce 600 million tonnes of grain with an average productivity of 5000 kg/ha (Jakarpong and Wiboon, 2017). In India, farmers grow many kinds of cereals, among them rice is grown in 43.86 million hectares, the production level is 112 million tonnes and the average productivity is about 2600 kg/ha. Rice is grown in almost all the states in the country. The insect-pest incidence is one of the major constraints for crop failure due to outbreaks of insect-pests have been reported worldwide (Reddy, 2013). Among various pests of rice, rice leaf folder is one of the most serious and most important pest of rice crop in Indian subcontinent.
It was earlier considered a minor pest but now a days it assumed major pest status. The shift in pest status is mainly attributed to changes in crop management practices, increased insecticides applications and weather parameters (Chakraborty and Deb, 2011). According to Bhanu and Reddy (2008), in favorable conditions leaf folder affected crop adversely resulting in severe loss in India. The loss may extend up to 63 to 80 per cent depending on agro-ecological situations as reported by Rajendran et al. (1986). Host plant resistance is an important component of integrated pest management (IPM) for sustainable rice production. Understanding the chemical and biochemical basis of resistance can facilitate the development of resistant varieties, thereby reducing dependence on chemical insecticides. The present study was therefore undertaken to investigate the chemical and biochemical basis of resistance in rice genotypes against rice leaf folder.
Conclusion
The rice genotypes Kala Namak, GNR-5, GNR-3, GRH-2, GNR-7, GR-15, GNRH-1, Mahsuri, GR-17, GNR-2 and NVSR-396 were identified as moderately resistant or least susceptible to rice leaf folder. These genotypes can serve as valuable resistance sources in breeding programmes for developing leaf folder-resistant varieties and strengthening integrated pest management (IPM). Biochemical and nutritional constituents were closely associated with rice leaf folder resistance. Higher nitrogen, phosphorus, crude protein, chlorophyll, soluble sugar and moisture contents were generally associated with greater leaf damage and larval population, whereas higher potassium, phenol and silica contents were associated with reduced infestation. Secondary nutrients and micronutrients showed mostly non-significant relationships with leaf folder infestation, indicating their comparatively limited contribution under the present conditions. Thus, lower N and P and higher K, phenol and silica contents may serve as useful biochemical indicators for identifying and screening leaf folder-resistant rice genotypes.
Limitations of the Study: The study was conducted at a single location (Navsari, Gujarat) over two seasons. The biochemical correlations are associative rather than causal, and the mechanisms underlying the observed associations were not investigated. Future research should include multi-location trials, mechanistic studies (e.g., antixenosis, antibiosis, tolerance), and investigation of the genetic basis of the biochemical traits associated with resistance.
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