Abstract
Breeding for nitrogen use efficiency (NUE) is important to deal with food insecurity and its effect on grain quality, particularly protein. A total of 1679 hybrids were evaluated in 16 different trials for grain yield (GY), grain quality traits (protein, starch and oil content) and kernel weight (KW) under optimum and managed low soil nitrogen fields in Kiboko, Kenya, from 2011 to 2014. The objectives of our study were to understand (i) the effect of low soil N stress on GY and quality traits, (ii) the relationship between GY and quality traits under each soil management condition and (iii) the relationship of traits with low-N versus optimum conditions. From the results, we observed the negative effects of low N on GY, KW and the percentage of protein content, and a positive effect on the percentage of starch content. The correlation between GY and all quality traits was very weak under both soil N conditions. GY had a strong relationship with KW under both optimum and low soil N conditions. Protein and starch content was significantly negative under both optimum and low-N conditions. There was no clear relationship among quality traits under optimum and low N, except for oil content. Therefore, it seems feasible to simultaneously improve GY along with quality traits under both optimum and low-N conditions, except for oil content. However, the negative trend observed between GY (starch) and protein content suggests the need for the regular monitoring of protein and starch content to identify varieties that combine both high GY and acceptable quality. Finally, we recommend further research with a few tropical maize genotypes contrasting for NUE to understand the relationship between the change in grain quality and NUE under low-N conditions.
Highlights
Maize is a staple food in sub-Saharan Africa (SSA) where it is the primary source of daily calorie and protein intake for more than 80 percent of the population [1]
The low correlation coefficient between grain yield under optimum and moderate low-N stress observed in our study indicates that only a few genes might be held in common for controlling grain yield under optimum and low soil N conditions
The increased percentage of starch content and the corresponding decrease in protein content under low soil N conditions could be an indication for increased stress tolerance, but there was no difference for grain composition between genotypes contrasting for nitrogen use efficiency (NUE) under both optimum and low-N conditions
Summary
Maize is a staple food in sub-Saharan Africa (SSA) where it is the primary source of daily calorie and protein intake for more than 80 percent of the population [1]. The average productivity of the crop (2 t/ha) in the region, is far below the world average (6 t/ha), partly due to the limited use of production inputs (e.g., N fertilizers) by small-scale farmers who cannot afford them [3,4]. Average fertilizer application in the world is 137 kg per ha, whereas in SSA, it is estimated to be less than 8 kg per ha, the lowest of any region in the world [4,5]. N is considered to be the most limiting in crop production [6]. Africa accounts for almost 20% of global land area under maize cultivation, it accounts only for less than 4% of N fertilizer application [2]
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