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Subject: Botany × Author: Amandeep Kaur × End date: 2018 × Start date: 2012 × Thesis Type: Ph.D ×
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    Physiological basis of nitrogen use efficiency in maize (zea maysl.) at various rates of applied nitrogen
    (PAU, 2012) Amandeep Kaur; Bedi, Seema
    Field and laboratory experiments were conducted at Punjab Agricultural University, Ludhiana during kharifseason in the years 2009 and 2010 respectively to study the physiological basis of nitrogen use efficiency in maize (Zea mays L.) at various rates of applied nitrogen. Six maize genotypes (hybrids and their parents) i.e., long duration PMH1 (parents LM13, LM14) and short duration JH3459 (parents CM143, CM144) were raised under five nitrogen levels viz; recommended (RDN), RDN+25%, RDN+50%, RDN-25% and RDN-50% respectively. Various ecophysiological traits viz; leaf area, leaf area index (LAI), fraction of PAR intercepted by plants (FRI), intercepted photosynthetically active radiation (IPAR), radiation use efficiency (RUE) were significantly improved with the application of nitrogen at higher than the recommended rates in both long and short duration genotypes. Low nitrogen levels increased anthesissilking interval and shortened the duration of grain filling. It also caused a reduction in grain yield and its determinants mainly harvest index, 100-kernel weight, cob weight, above ground biomass, shelling percentage, cob length and diameter, number of kernel rows per cob and number of kernels per cob. The various physiological traits such as plant height, crop growth rate, relative growth rate, dry matter accumulation, root-shoot ratio etc. were significantly increased with the application of 25% and 50% higher nitrogen than the recommended. The applied nitrogendose also affected the content of various biochemical constituents (total soluble sugars, total soluble proteins, total starch content, chlorophyll content as well as the activity of various enzymes viz., nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT) and PEP carboxylase). Path coefficient analysis showed that various traits such as RUE, LAI, FRI, IPAR, GS and NR activity had the maximum positivedirect contribution to grain yield in both set of maize genotypes (long and short duration). Therefore, these traits should be used as target traits to improve maize grain yield at both high and low nitrogen levels. The various quality parameters (starch, proteinand oil) in grains of both long and short duration genotypes were maximum in the treatment RDN+50%. Aminoacid content (total free amino-acids, tryptophan and methionine content) was significantly decreased with the decrease in nitrogen (RDN-25%; RDN-50%) than the recommended. In contrast, there was a decreasing pattern in nitrogen use efficiency (NUE), nitrogen remobilization efficiency (NRE) and nitrogen harvest index (NHI) values with increasing fertilizer rates in both long and short duration genotypes. Hybrids i.e. PMH 1 (long duration) and JH 3459 (short duration) were more responsive to variations in nitrogen supply than their female and male parents. Moreover, the high nitrogen use efficiency for hybrids (PMH1, JH3459) as compared to their parents (LM13, LM14 ; CM143, CM144) was associated with greater PAR interception during the growth period , high radiation use efficiency (RUE), more harvest index (HI), high photosynthetic capacity associated with increased acitivity of PEP carboxylase enzyme and high chlorophyll content in leaves, high nitrogen metabolic efficiency, increased activity of nitrogen metabolism enzymes (nitrate reductase, glutamine synthetase and glutamate synthase) leading to higher nitrogen harvest in dex. Keywords:GOGAT, GS, maize, nitrogen, NR, NUE, PAR, PEP carboxylase, RUE, yield