Abstract:
Variability has been reported on wheat for different traits including nitrogen use efficiency (NUE). However there is limited information on NUE variability among wheat cultivars in eastern Ethiopia. Study was conducted to assess genetic variability in NUE among twenty bread wheat cultivars and to assess the association among traits in bread wheat at Haramaya University under two N levels (0 and 41 kg N/ha in 2017 cropping season. The cultivars were evaluated in split plot design with three replications. The main and sub-plot were N fertilizer rate and cultivars, respectively. Data were collected on different agronomic and NUE traits. Nitrogen fertilizer showed significant effect for all traits, except days to heading (DTH) and grain filling duration (GFD), while cultivars exhibited significant difference (p≤.01) for all traits. Interaction of N and cultivars showed highly significant difference (p≤0.01) for all traits, except DTH, GFD, plant height (PH), number of grains per spike (NGPS) and above ground biomass (AGB). Kakaba (at 57.83 days) and Huluka (at 84.83 days) headed earlier and later than others, respectively. The highest and the lowest for GFD were due to cultivars Wane and Huluka, respectively. Alidoro was the tallest and KBG-1was the shortest. Wane and Millennium gave the highest (29.41 ton ha-1) and lowest (15.91 ton ha-1) AGB. The highest and lowest NGPS were from Ogolcho and Hoggana. Early (110.00 days) maturing Katar and very late (132.67days) maturing was Wane. Alidoro developed longest (12.00 cm) SL than with application of 41 kg N/ha and the shortest (6.03cm) without N. Danda’a gave the highest (8.04 ton ha-1) grain yield (GY) than other with 41 kg N/ha and Millennium gave lowest (2.38 tonha-1) without N applied. The highest (47.26 %) harvest index (HI) was obtained from Mitike with 41 kg N/ha while the lowest (9.70 %) from Tusie without N applied. The highest (45.83g) and the lowest (30.67g) thousand kernel weight (TKW) obtained from Lemu and Kingbird. The highest total nitrogen (TN) obtained from Danda’a and the lowest from Bobicho without N applied. The lowest (14.20%) and highest (99.34%) nitrogen harvest index (NHI) were recorded from Huluka and Danda’a without applied N and 41 kg N/ha. The highest 1.02% grain protein content (GPC) obtained from Tusie without N with application of 41 kg N/ha and lowest 0.15% from Kubsa without applied N. But, Hoggana and Kingbird exhibited better GPC for without N than with N. The highest (39.04 gg-1m-2) and lowest (2.89 gg-1m-2) NUE were recorded from without N for KBG-1 and lowest for Kubsa. Trait NUE ranged from 2.89 to39.04 gg-1m-2. Phenotypic coefficient of variation (PCV) values was greater than genotypic coefficient of variation (GCV) values for all study traits. The PCV, GCV, broad sense heritability and genetic advance estimates ranged between low and moderate for most traits. Trait HI and NHI showed significant positive correlation at genotypic and phenotypic level with GY. Genotypically, GY was negatively correlated with DTH, DTM, TN and NUE and positively correlated with TKW, NGPS and GPC. Phenotypically, NHI showed highly significant and positive correlation with GY. Moreover, PH, NSPM, TKW and GPC had positive correlated with GY. Path coefficient analysis revealed that AGB and HI exerted high and favorable direct effects on GY. The maximum positive genotypic direct effect on GY was exerted by HI and highly significant positive genotypic correlations. The below conclusions can be drawn from the present study. Kingbird was found better performance in GY, NHI and NUE. Generally, among all tested cultivars Kingbird was the best cultivar because of its high nitrogen use efficiency and grain yield production. Therefore, if farmers use this cultivar, they can get a benefit of maximizing their productivity, reduce cost of production due to nitrogen fertilizer, at the same time they reduce environmental pollution. However, since this is a one-year result, it is necessary to repeat the field experiment and evaluate the genotypes over several locations and years in order to make conclusive and comprehensive conclusion and recommendations.