Developing N use efficient potato varieties requires exploring the genetic basis of nitrogen use efficiency (NUE) and associated agronomic and physiological traits. In order to identify QTLs for NUE and NUE-related traits, and to determine the relationships between the traits and QTLs in potato, a diploid potato mapping population (CxE) was evaluated in the field in Ethiopia under low and high N fertilizer levels. QTL detection was performed using interval mapping and multiple QTL mapping (MQM). A total of 52 putative QTLs were identified for ten traits, of which 28 QTLs were detected under low N availability while the remaining 24 QTLs were detected under high N conditions. Several QTLs were location and N level specific, suggesting the presence of QTL x environment interaction. A region on linkage group V (21-38 cM) accumulated the largest number of QTLs. This region coincides with the earliness locus encoded by the CDF1 gene, suggesting that earliness has a profound influence on NUE. A putative second QTL region on linkage group V located 20 cM from the earliness locus (38-56 cM) and a region on linkage group IV (60-72 cM) might be useful other regions to focus on, for NUE improvement in potato. To verify the stability of the identified QTLs and to use these for the detection of possible candidate genes, further multi-environment trials with larger population size may be required. ResumenEl desarrollo de variedades de papa eficientes en el uso del N requiere de la exploración de las bases genéticas en la eficiencia del uso del nitrógeno (NUE) asociadas a caracteres agronómicos y fisiológicos. A fin de identificar QTLs para NUE y para rasgos relacionados con NUE, y para determinar las relaciones entre los caracteres y QTLs en papa, se evaluó un mapa de población de papa diploide (CxE) en el campo en Etiopia en niveles bajos y altos de fertilizante nitrogenado. La detección de QTL se efectuó usando mapeado a intervalos y mapeo múltiple de QTL (MQM). Se identificaron un total de 52 posibles QTL para diez rasgos, de los cuales 28 QTL se detectaron en baja disponibilidad de N, mientras que los restantes 24 se detectaron en altas condiciones de N. Varios QTL fueron específicos para localidad y nivel de N, sugiriendo la presencia de la interacción QTL x ambiente. Una región de agrupamiento ligado V (21-38 cM) acumuló el mayor número de QTLs. Esta región coincide con el locus de precocidad codificado por el gen CDF1, lo que sugiere que la precocidad tiene una influencia profunda en NUE. Una supuesta segunda región QTL en el grupo de ligamiento V localizado a 20 cM del locus de precocidad (38-56 cM) y una región del grupo de ligamiento IV (60-72 cM) pudiera ser útil para enfocarse en otras regiones, para mejoramiento de NUE en papa. Para verificar la estabilidad de los QTL identificados y para usarlos en la detección de posibles genes candidatos, se pudieran requerir ensayos multiambiente posteriores con tamaños mas grandes de población.
Developing cultivars that use nitrogen more efficiently is a sustainable strategy for reducing nitrogen use in crop production. To assess the genetic diversity for nitrogen use efficiency (NUE) and related traits in potato, a total of 97 (88 for the Western-European market and 9 Ethiopian) cultivars were evaluated at two nitrogen levels (40 kg/ha and 120 kg/ha) for 24 quantitative traits in Debre-Tabor and Injibara (Ethiopia) in the 2013 main rainy season (June to September). Highly significant variation was found among genotypes for almost all measured traits. Plant height, NUE, tuber yield, and yield-related traits and model parameters for canopy development (maximum canopy covers area under the canopy curve) were significantly affected by N levels across locations. Dutch cultivars had more rapid initial canopy development and matured earlier than the Ethiopian cultivars at both N levels and locations. A hierarchical cluster analysis grouped the cultivars in 9 and 11 genetically distinct classes at low and high N, respectively. The genetic component accounted for a large portion of the phenotypic variation for plant height, tuber number per plant, average tuber weight, and NUE under both N regimes, as indicated by a high heritability. Strong phenotypic correlations were observed between NUE and tuber number per plant, days to maturity, tuber dry matter %, maximum canopy cover, and area under the canopy curve under both low and high N conditions. The result is indicative to set the best parental line selection criteria for crossing purpose and utilize the cultivars for further potato NUE breeding programmes.
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