Influence of Solar Radiation and Vapour Pressure Deficit on Transpiration Efficiency of Rainfed Sorghum

Besides assimilation, plant water relations are important aspects of physiological basis of productivity of crops in water limited environment. The relationships of photosynthesis rate, transpiration rate, leaf water potential and stomatal conductance with photosynthetically active radiation (PAR) and vapour pressure deficit (VPD) during pre-flowering (panicle initiation to ear emergence) and grain filling (from anthesis to maturity) stages of a sorghum hybrid (cv. CSH-6 ) grown under rainfed conditions were studied. Photosynthesis rate declined when PAR was above 1300 μmol m⁻² s⁻¹. during both the growth stages. Higher transpiration rate during grain filling stage at higher PAR caused the transpiration efficiency to be lower than during pre-flowering stage when PAR was above 1200 μmol m⁻²s⁻¹.Leaf water potential and stomatal conductance decreased with increase in PAR. Leaf water potential was higher during pre-flowering than during grain filling stage but maximum photosynthesis rate was similar during both the growth stages. Changes in VPD did not qualitatively alter the relationships of the physiological variables with PAR.
Decreasing photosynthesis rate and LWP at high PAR suggest that photosynthesis rate was limited by low leaf water potential when PAR was optimal, and by low PAR even when leaf water potential was high in rainfed sorghum during rainy season.     

Tagging of Brown Planthopper Resistance Genes in F2s of IR50 × Ptb33 of Rice by Using Bulked Segregant Analysis

Brown planthopper(Nilaparvata lugens St?l) is one of the most damaging pests causing hopper burn in rice,and thereby reducing the productivity and also the quality of the product.The effective management strategy to control this pest is the identification and transfer of desirable genes to local rice cultivars.The most important approach for developing resistant cultivars is the identification of markers,which can help in marker-assisted selection of more durable resistant genotype.The susceptible parent IR50 and the resistant parent Ptb33,and their F2 populations were used in bulked segregant analysis for identification of resistant genes with random amplified polymorphic DNA marker(RAPD) primers.The primers OPC7 and OPAG14 showed both dominant and susceptible specific banding pattern so called co-dominant markers.Moreover,OPC7697 and OPAG14680 showed resistant specific bands and thus being in coupling phase,whereas OPC7846 and OPAG14650 showed susceptible specific genotypic bands in bulked segregant analysis.Therefore,the coupling phase markers,OPC7697 and OPAG14680,are considered to be more useful in marker-assisted selection of rice genotypes in crop improvement.