Evaluation of nitrogen use efficiency of mutant and parental varieties of rice in Chhattisgarh

Introduction

Nitrogen-use efficiency (NUE) is a parameter which indicates the extent of utilization of applied N by the crop and evaluates a crop cultivar. It is also defined as the ratio of grain yield to supplied N. Since, one of the major challenges faced by us is to ensure adequate availability of nutrients and rational use of appropriate fertilizers for agriculture, in view of preventing the unwanted accumulation of reactive N from different sources and improving nutrient use efficiency of crops . Therefore, vital factor for crop improvement in agriculture is improving nitrogen use efficiency for achieving sustainability . Mutation breeding is the process of exposing seeds to mutagens (such as chemicals or radiation) to produce mutants with desired characteristics . It is the most effective and simple way to generate variability in crop plants to select the desired plant phenotype . Compared with other traditional breeding methods , it takes less time to develop varieties through mutation breeding. Indira Gandhi Agriculture University (IGAU) was developed two new high-yielding mutant varieties of paddy (C.G. Javaphool Trombay and Sonagathi Mutant-1) in collaboration with Bhabha Atomic Research Centre (BARC), which are shorter in height and take less duration to ripe. Both the varieties were developed by using physical mutagen gamma rays (300 Gy) through genetic mutation of traditional varieties of paddy Sonagathi and Javaphool. Higher grain yield and higher nitrogen use efficiency are associated with understanding plant traits like root-shoot biomass, root length, root length density, root oxidation activity and crop growth rate, photosynthetic NUE etc. These traits are important in breeding program to develop N-efficient varieties (Ju et al., 2015) [8] . Improvement of dry matter weight, nitrogen uptake ability per panicle and nitrogen uptake intensity per panicle are helpful to improve the amount of nitrogen uptake.

Increase in nitrogen translocation from vegetative organs to reproductive organs (panicles) and decrease of the nitrogen content in sheath, stem and leaves are beneficial for the improvement of nitrogen use efficiency in Indica and Japonica rice varieties with longer growth duration (Hongcheng et al., 2013) [5] .

Materials and Methods

The experimental site "Research Farm of Indira Gandhi Krishi Vishwavidyalaya" lies at 21º 16.885'' N latitude and 81º 42.117''E longitudes with an altitude of 298.56 meter above the mean sea level. Two traditional varieties of paddy and their mutant varieties were laid out in split plot design with varying doses of nitrogen. Grain and straw yields were recorded plot wise and estimation was done on hectare basis. The representative 5 plant samples were selected randomly for taking observations of various morphophysiological parameters like plant height, panicle length, number of effective tillers per plant, number of filled grains per panicle, test weight, grain and straw yield. Nutrient content analysis of plant samples was also done. Likewise, soil samples were pooled and collected from three different sites of plot. Soil pH was determined by electrode pH meter as suggested by Piper (1966) [14] . Electrical Conductivity of soil sample was determined by EC meter by dipping the electrode without stirring as described by Black (1965) [2] . Organic carbon was determined by Walkley and Black's (1934) [18] rapid titration method as described by Piper (1966) [14] . Available N was determined by alkaline permanganate method as suggested by Subbiah and Asija (1956) [17] . Available soil phosphorus was extracted by 0.5 M NaHCO3 at pH 8.5 using Double beam Spectrophotometer as described by Olsen et al., (1954) [12] . Soil available potassium was extracted by 1 N (neutral) ammonium acetate and determined with the help of flame photometer as described by Jackson, (1967) [6] . Total Nitrogen content of plant samples were determined by Kjeldahl's digestion method using automatic KEL plus distillation described by Chapman and Pratt (1961) [3] . Phosphorus content was determined by vanado-molybdate yellow color complex method as described by Jackson (1973) [7] . Potassium content was determined by Flame photometer as described by Chapman and Pratt (1961) [3] . Nutrient uptake was calculated by using the following formula:

The easiest way to calculate NUE is Apparent Nitrogen Recovery (ARN) Where, TUN-total N uptake from fertilized plot (kg/ha) CUN-total N uptake from unfertilized plot (kg/ha) AFN-amount of applied N fertilizer (kg/ha)

Results and Discussion

The results of the study area are presented and discussed as follows:

As per the data recorded, plant height increased with increasing nitrogen levels . This result is in accordance with an experiment conducted by Gewaily et al., (2018) [4] . This may be because of its role in promoting rapid leaf, stem and other vegetative part's growth and development. Among four nitrogen levels, N100 produced highest plant height (149.59 cm), whereas, lowest (129.24 cm) by N0. In case of varieties, highest plant height (155.49 cm) was recorded by V2 (Javaphool parent), whereas lowest (130.97 cm) by V3 (Sonagathi mutant-1). On comparing parent varieties to their mutant types, parent varieties showed significantly higher plant height. The plant height was significantly reduced due to mutation in both varieties . Interaction effect of nitrogen levels and varieties on plant height was found to be nonsignificant.

Number of effective tillers per hill

The results revealed that variety V3 (Sonagathi mutant-1) recorded highest number (6.46) of effective tillers. Among nitrogen levels, application of N100 produced maximum number of effective tillers (6.27). This clarifies that on increasing nitrogen levels , number of effective tillers per hill increases. This is because nitrogen application increases the cytokinin content within tiller nodes and thus enhanced the germination of the tiller primordium (Liu et al., 2011) [10] . On comparing parent varieties to their mutant types , mutant varieties showed significantly higher number of effective tillers per hill than parent varieties . N -0.14, V-0.23, N X V -0.46 CD (p = 0.05) N -0.47, V -0.67, N X V -NS

Panicle length tends to increase with increasing nitrogen level up to N80 and after that it was decreased. Similar trend was also reported by Aparna (2017) [1] . Among all varieties, V1 (C.G. Javaphool Trombay) produced highest panicle length i.e. 27.44 cm whereas, lowest i.e. 24.94 cm by V4 (Sonagathi parent). Application of N₀ resulted in minimum panicle length (Salman et al., 2012) [15] . On comparison, mutant varieties showed higher panicle length and which was at-par with their parents. The highest number of filled grains per panicle (196.43) was produced under N100 and lowest in N0. Result revealed that on increasing N levels , number of filled grains also increased. This is due to adequate supply of photosynthates from the source to the sink (grain). Accumulation of photosynthates to sink depends on the availability of nutrients and genetic potentiality of the crops (Yesuf and Balcha, 2014) [19] . The test weight was not affected due to mutation; therefore Sonagathi varieties had greater test weight than Javaphool. Highest test weight (23.24 gm) was found for V3 (Sonagathi mutant-1) and lowest test weight (10.46gm) was found for V2 (Javaphool parent). Significant differences were observed among two varieties but differences among various nitrogen levels were found to be non-significant. This may be because test weight of variety is genetically inherent character. Interaction effect of varieties with nitrogen levels on test weight was also found to be nonsignificant. Nitrogen use efficiency Among four varieties, V3 (Sonagathi mutant-1) (30.12%) was found to be superior with respect to N-use efficiency over others. In case of nitrogen applications , the highest NUE (29.98%) was observed in N₈₀ (80 kg/ha) levels. Data revealed that NUE firstly increased with increasing N doses up to N₈₀ (80 kg/ha) levels, after that, it decreased at N₁₀₀.

Similar results were found by Shivay Y.S. et al., (200) [13] . Interaction effect of varieties with nitrogen levels (N×V) influenced the grain yield. Varieties Sonagathi mutant-1 (V3) and Sonagathi parent (V4) significantly increased the grain yield up to 80 kg N / ha whereas C.G. Javaphool Trombay (V1) and Javaphool parent (V2) responded only up to 60 kg N / ha. This might be due to higher nitrogen uptake at higher nitrogen supply which ultimately led to biomass production through enzymatic activities like glutamine synthetase, glutamate synthase and glutamate dehydrogenase. (Miflin and Habash., 2002) [22]

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