High nitrogen (N) rate often leads to low yield of rice due to lodging and mutual shading. This study was conducted to ascertain whether silicon (Si) could enhance yield response of rice to higher N rate by enhancing rigidity of plant parts and improving photosynthesis. The effects of Si and N on crop growth, photosynthesis, N use efficiencies and yield of rice were investigated during wet season (June to November) in sub-humid tropical region of India. An increasing trend in crop growth rate with Si at all levels of N was observed. Silicon reduced the flag leaf angle making the leaf more upright and enhanced flag leaf N content. Leaf chlorophyll concentration and single leaf photosynthesis rate were higher with Si compared to without Si at flowering stage. Both N and Si significantly affected panicle number and grain filling.Application of 200 kg SiO 2 ha −1 and 100 kg N ha −1 produced the highest number of panicle per square meter, filled grain per panicle and yield. Significant yield increases ranging from 8.2-16.9% were observed with Si compared to without Si. Both N and Si treatments had significant effects on N uptake and N use efficiency. Agronomic N use efficiency and N recovery efficiency were higher with Si compared to without Si. The highest physiological N use efficiency was recorded with 200 kg SiO 2 ha −1 and 80 kg N ha −1 . Silicon may enhance yield response of rice to higher N rate by improving source (photosynthetic) capacity and sink (reproductive organ) strength.Abbreviations: DMA, dry matter accumulation; FL, flowering; HI, harvest index; MT, maximum tillering; NRE, nitrogen recovery efficiency; NUE a , agronomic nitrogen use efficiency; NUE p , physiological nitrogen use efficiency; PFP N , partial factor productivity of nitrogen; PI, panicle initiation; PM, physiological maturity.
Drought stress is the most devastating abiotic stress which severely affects starch biosynthesis, thus altering the glycemic index (GI) of rice grains. It shortens the period of grain filling by rapidly translocating assimilates to grains, thereby decreasing amylose content (AC), resistant starch (RS), and increasing GI value. Among 30 genotypes tested, ZHU-11-26, IR 20, and Annada differ in exhibiting a much lower reduction in AC and RS which result in insignificant change in GI (<1) under drought stress. Two genotypes (ZHU-11-26 and Pathara) are selected for granule bound starch synthase I expression analysis on the basis of their contrasting GI and RS content. The gene is highly and significantly expressed at the dough stage of grain development and shows a positive association between its expression and RS content. Drought is very common in most parts of the world in the present climate-change scenario, where even mild terminal stress may affect grain filling rate and cause the increment in GI value of grains. In this context, identification of less responsive genotypes with a lesser change in GI under drought stress may help in developing rice varieties for the diabetics even grown under stress-prone environments.
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