Padmavathi Chintalapati

Initial evaluations of the System of Rice Intensification in India and elsewhere focused mainly on its impacts on yield and income, and usually covered just one or two seasons. Researchers at the ICAR-Indian Institute of Rice Research have conducted a more comprehensive evaluation of SRI methods over six years (six wet and six dry seasons), comparing them with three alternatives: modified, partially mechanized SRI (MSRI) to reduce labor requirements; direct-seeded rice (DSR) as an alternative method for growing rice; and conventional transplanting of rice with flooding of fields (CTF). Grain yield with SRI methods was found to be about 50% higher than with CTF (6.35 t ha⁻¹ vs. 4.27 t ha⁻¹), while the MSRI yield was essentially the same (6.34 t ha⁻¹), 16% more than with DSR (5.45 t ha⁻¹). Water productivity with SRI methods was 5.32–6.85 kg ha-mm⁻¹, followed by 4.14–5.72 kg ha-mm⁻¹ for MSRI, 5.06–5.11 kg ha-mm⁻¹ for DSR, and 3.52–4.56 kg ha-mm⁻¹ for CTF. In comparison with CTF, SRI methods significantly enhanced soil microbial populations over time: bacteria by 12%, fungi by 8%, and actinomycetes by 20%. Biological activity in the rhizosphere was also higher as indicated by 8.5% greater dehydrogenase and 16% more FDA enzymes in soil under SRI management. Similarly, an indicator of soil organic matter, glucosidase activity, was 78% higher compared to CTF. SRI enhanced the relative abundance of beneficial microbial-feeding nematodes by 7.5% compared to CTF, while that of plant-pathogenic nematodes was 7.5% lower under SRI. Relative to conventional methods, SRI management reduced GHG emissions by 21%, while DSR reduced them by 23%, and MSRI by 13%, compared to standard rice-growing practice. Economic analysis showed both gross and net economic returns to be higher with SRI than with the other management systems evaluated. While the six-year study documented many advantages of SRI crop management, it also showed that MSRI is a promising adaptation that provides similar benefits but with lower labor requirements.

Initial evaluations of the System of Rice Intensification in India and elsewhere have mainly fo-cused on its impact on yield and income and have usually covered just one or two seasons. Re-searchers at the ICAR-Indian Institute of Rice Research conducted a more comprehensive evalua-tion of SRI methods over six years (six wet and six dry seasons), comparing these methods with three other rice crop management systems: modified, partially mechanized SRI (MSRI); direct-seeded rice (DSR); and normal transplanting with inundated fields (NTP). SRI grain yield was found to be about 50% higher than with NTP (6.35 t ha-1 vs 4.27 t ha-1), while the MSRI yield was essentially the same (6.34 t ha-1) and 16% higher than with DSR (5.45 t ha-1). Compared to NTP, SRI methods significantly enhanced soil microbial populations over time, bacteria by 12%, fungi by 8%, and actinomycetes by 20%. Indicators of biological activity in the rhizosphere were also higher, dehydrogenase by 8.5% and FDA enzymes by 16%. Glucosidase activity, an indicator of soil organic matter, was 78% higher. Relative to normal transplanting methods, SRI reduced GHG emissions by 21%, while DSR reduced them by 23% and MSRI by 13%, which indicated pos-itive effects of the alternate and improved methods over normal transplanting. Economic analy-sis showed that both gross and net economic returns to be higher with SRI than with MSRI and the other management systems evaluated. While the six-year study documented many ad-vantages of SRI crop management, the MSRI version evaluated is a promising adaptation that provide similar benefits but with lower labor requirements.

The System of Rice Intensification (SRI) developed in Madagascar has spread to many parts of the world, including India. This study assessing insect pest prevalence on rice grown with SRI vs. conventional methods at multiple locations in India was prompted by reports that SRI-managed rice plants are healthier and more resistant to pest and disease damage. Field experiments were conducted under the All-India Coordinated Rice Improvement Project over a 5-year period. The split-plot design assessed both cultivation methods and different cultivars, hybrids and improved varieties. Across the eight locations, SRI methods of cultivation showed a lower incidence of stem borer, planthoppers, and gall midge compared to conventional methods. Whorl maggots and thrips, on the other hand, were observed to be higher. Grain yield was significantly higher with SRI management across all locations. Higher ash, cellulose, hemicellulose, as well as silica content in rice plants under SRI management could explain at least in part the SRI plants’ resistance to pest damage. Analysis of guild composition revealed that in SRI plots, there were more natural enemies (insect predators and parasitoids) present and fewer crop pests (phytophages). A meta-analysis that considered other published research on this subject revealed a lower incidence of dead hearts, white ear-heads, and leaf folders, along with higher grain yield, in SRI plots.

The rice leaf folder,Cnaphalocrocis medinalisGuenée (Lepidoptera: Crambidae), an important foliage feeding insect in rice,Oryza sativaL. (Poaceae), is widely distributed throughout Asia, causing frequent outbreaks and considerable yield losses. Mutants of the rice strain Samba Mahsuri (MSM) represent unique plant material and are explored here for the first time for resistance to the rice leaf folder. Stringent rapid field screening for two consecutive seasons led to the identification of 10 lines as moderately resistant, with low damage area as well as low damage score. Upon assessment of various morphological traits potentially contributing to the resistance, damage area was negatively correlated with leaf length and positively with leaf width. Among the biochemical traits, leaf nitrogen content was positively correlated with leaf folder damage whereas silica was negatively correlated. Oviposition preference by leaf folder adult moths and larval settling preference were low on MSM 139 and MSM 127. We also observed that leaf folder larvae took more time for leaf selection (3.1 min) and making a primary fold (41.5 min), with more head swings (846) in moderately resistant MSM lines. Similarly, in these lines, leaf folders showed a low intrinsic rate of increase (r_m = 0.15 females per female per day), low weekly multiplication rate (2.85), and low net reproductive rate (R₀ = 137.5 females per female per generation) with increased generation time (T = 32.8 days) and doubling time (4.5 days), indicating their relatively poor population growth potential. Overall, the moderately resistant mutant lines we identified showed reduced ovipositional preference and larval settling preference, extended larval developmental period with low survival, reduced primary fold length, and an increased number of binds and head swings with a low intrinsic rate of increase resulting in reduced population build‐up. These lines possessing a good genetic makeup have a great potential to be used in breeding programs for the development of leaf folder resistant varieties.

Rice leaffolder, Cnaphalocrocis medinalis is one of the key foliage feeding insects of great concern throughout Asia as it results in significant yield losses. High visibility of damage is triggering farmers to apply toxic pesticides for its management. Therefore, it is vital to identify new stable sources of resistance for leaffolder. Phenotyping of 160 recombinant inbred lines (RILs) of a cross between a resistant parent, W1263 and a susceptible parent, TN1 using a rapid field screening method for three seasons resulted in identification of nine RILs as stable sources of resistance to rice leaffolder. Phenotypic frequency distributions were found continuous indicating that the resistance is a quantitative trait governed by polygenes. Phenotypic data for three seasons were analyzed using Genotype and Genotype × Environment Interaction (GGE) analysis for identification of stable resistant lines. Additive main effect and multiplicative interaction (AMMI) analysis showed that 86.41% of the total sum of square of damaged leaf area was attributed to genotype (GEN) effect; 0.48% to environment (ENV) effects and 5.68% to genotype by environment (G × E) interaction effects. Damage area, damage score and leaf length showed very high broad-sense heritability across three environments. However, leaf width had low heritability indicating higher environment influence. Phylogenetic analysis grouped these 160 RILs and parents into five clusters based on resistant reaction. AMMI and GGE biplot analysis revealed that stable genotypes G8 (MP114) and G3 (MP108) with lower damage area and damage score can be utilized in developing cultivars with leaffolder resistance.

BACKGROUND: Among the neonicotinoids, imidacloprid and thiamethoxam have been frequently used in planthopper endemic areas. Wherever leaffolder incidence occurs along with planthoppers in rice fields, use of neonicotinoids has resulted in increase in leaffolder population. The present study was carried out to verify and confirm the resurgence, as well as to identify factors contributing to resurgence. RESULTS: In imidacloprid‐ and thiamethoxam‐applied plots, a 17.5–217.5% increase in leaffolder population over the untreated control was observed. Neonicotinoids showed moderate toxicity to eggs with 60% survival, while 37–60% of larvae reached adult stage. The larval duration was also reduced. Fecundity was stimulated, with a 6.2–37.21% increase over the untreated control. A significant positive correlation was observed between larval population and total soluble sugars in thiamethoxam treatment ( r = 0.9984, P ≤ 0.01). CONCLUSION: Stimulated fecundity on neonicotinoid‐sprayed plants, coupled with reduced larval duration and low egg toxicity, could be the major factors contributing to the upsurge of leaffolder. This study aids in cautioning farmers to be more vigilant while using imidacloprid and thiamethoxam, particularly in rice fields where leaffolder exists alongside planthoppers. © 2015 Society of Chemical Industry

The rice leaf folder, Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) is a predominant foliage feeder in all the rice ecosystems. The object

Influence of leaffolder feeding on chlorophyll, PS II activity and plant–water relations, effect of larval density on leaf damage and time course studies on larval feeding behaviour on altered physiological changes in TN1 rice culture were studied. Quantification of yield losses in the field caused by leaffolder was also assessed. Leaffolder damage resulted in 57% reduction in chlorophyll content, 23% reduction in PS II activity and 23% reduction in relative water content in comparison with control. Rice leaffolder larva folds the leaf and scrapes the green tissue from within the fold resulting in scorching and drying of the leaves. Larval density had differentially influenced effective leaf area of rice crop. Larval densities of more than 3 larvae per hill at maximum tillering stage resulted up to 20% unfilled grains, 28–57% reduction in PS II activity and 23% reduction in relative water content in comparison with the control. At flowering stage, flag leaf area damage of above 25% resulted in more than 50% unfilled grains over control, indicating direct effect of yield reduction in rice. Thus, a cumulative effect of loss in chlorophyll, reduced photosynthate availability and altered water relations caused by the leaffolder injury to flag leaf lead to greater yield loss in rice.