Nitrogen use efficiency in bread wheat: Genetic variation and prospects for improvement.

Nitrogen (N) is one of the primary macronutrients required for crop growth and yield. This nutrient is especially limiting wheat yields in the dry and low fertile agro-ecologies having low N in the root zone soil strata. Moreover, majority of farmers in India and South Asia are small to marginal with meagre capacity to invest in costly nitrogen fertilizers. Therefore, there is an immense need to identify lines that use nitrogen efficiently. A set of 50 diverse wheat genotypes consisting of indigenous germplasm lines (05), cultivars released for commercial cultivation (23) and selected elite lines from CIMMYT nurseries (22) were evaluated in an alpha-lattice design with two replications, a six-rowed plot of 2.5m length for 24 agro morphological, physiological and NUE related traits during two consecutive crop seasons in an N-depleted precision field under two different N levels of 50%-N50 (T1) and 100%-N100 (T2) of recommended N, i.e., 100 kg/ha. Analysis of variance revealed significant genetic variation among genotypes for all the traits studied. About 11.36% yield reduction was observed at reduced N levels. Significant correlations among NUE traits and yield component traits were observed which indicated pivotal role of N remobilization to the grain in enhancing yield levels. Among N-insensitive genotypes identified based on their yielding ability at low N levels, UASBW13356, UASBW13358, UASBW13354, UASBW13357 and KRL1-4 showed their inherent genotypic plasticity toward N application. The genotypes with more yield and high to moderate NUtE can be used as parents for the breeding of N efficient genotypes for marginal agro-ecologies. Low N tolerant genotypes identified from the current investigation may be further utilized in the identification of genomic regions responsible for NUE and its deployment in wheat breeding programs. The comprehensive data of 24 traits under different nitrogen levels for diverse genotypes from India and global sources (mainly CIMMYT) should be useful for supporting breeding for NUE and thus will be of great help for small and marginal farmers in India and South Asia.

First report of Fusarium poae Causing Fusarium head Blight of Wheat in India.

Wheat is one of major cereal crops with paramount importance that is cultivated across the globe. Fusarium head blight (FHB) is a catastrophic disease of wheat which has recently risen to prominence due to its direct impact on the quality and quantity of wheat on a global scale. During a field survey conducted in Rabi 2021-22, wheat spikes showing characteristic symptoms of head blight were observed in northern parts of the Karnataka, India, in the districts Bagalkote, Belagavi and Dharwad. The infected spikelets from the heads with symptoms of infection were washed well in distilled water and surface sterilized using 1% sodium hypochlorite solution. They were further washed using sterilized distilled water to remove the traces of sodium hypochlorite. These spikelets were then transferred to sterile potato dextrose agar (PDA) plates under aseptic conditions. The plates were incubated at a temperature of 27±1°C for ten days to obtain good fungal growth. The fungus produced white to orangish pink, dense mycelia and hyaline septate hyphae. Macroconidia were sickle-shaped measuring 35.7 to 52.6 x 3.2 to 5.1 µm, dorsoventrally curved with an elongated basal cell ending in a prominent long foot; the apical cell was also elongated, tapered, slightly curved. Spores had 3 to 4 cells and formed on monophialide. Microconidia and chlamydospores were present only in a few isolates. Fungal genomic DNA was extracted from all the established isolates using CTAB (Cetyl-trimethyl ammonium bromide) method (Murray and Thompson, 1980). The ITS region of r-DNA and translation elongation factor-1 alpha (TEF-1α) genes of the ten isolates were amplified using ITS1/ITS4 primer pair (White et al. 1990) and the species-specific EF1F/EF1R primer pair (O'Donnell et al., 1998) respectively, to detect and distinguish within Fusarium species. The results exhibited 95% similarity with Fusarium poae with GenBank Accession No. XMO44849482.1. which was previously reported as a causal agent of Fusarium head blight of wheat in Georgia, USA. The TEF1-α sequences were deposited in the GenBank and the accession numbers from OP716756 to OP716765 were obtained. For the pathogenicity test, spore suspension containing a load of 108 conidia ml-1 was prepared from ten days old Fusarium poae culture and sprayed on the healthy wheat heads of the susceptible variety UAS-304 during anthesis stage by using hand atomizer. Control plants were sprayed in a similar manner with sterile distilled water. In order to enhance disease development and increase the accuracy of the evaluation, humidity was maintained for 72 hours post-inoculation period by covering each spike with a plastic bag and misting at least once daily. The characteristic head blight symptoms were observed in the inoculated wheat spikes. No symptoms were noticed in the water-treated control. The plants initially showed bleaching in single spikelet after seven days of inoculation, which eventually spread to the entire spike. After fourteen days of inoculation, the spikes showed blighted appearance with pinkish or orangish mass of mycelia grown on the affected region. The pathogen was further reisolated from the infected plants and examined under the microscope. The similar morphological features as that of the originally inoculated pathogen was observed, hence fulfilling Koch's postulates. To our knowledge, this is the first report of Fusarium poae causing head blight of wheat in India. Keeping the current climate change scenario in view, the plausibility of this pathogen causing a major havoc in the near future must not be ignored, considering the fact that it has a wide host range and highly evolving nature. The ubiquity of the Fusarium head blight recently in northern parts of Karnataka urges the need to conduct further studies on the variability, distribution and management of the pathogen.