Early indirect selection for nitrogen use efficiency in maize

Abstract

-Several studies to evaluate nitrogen use efficiency (NUE) have been carried out using early growth stages. However, there are no scientific reports on the ideal stage for evaluation and on which characteristics have the highest correlation with the NUE at that stage. The aim therefore was to identify the phenological stages and secondary characteristics which maximize accuracy in early indirect selection for NUE in maize. To do this, three endogamic maize strains were evaluated in a completely randomised design with five replications, in a triple factorial scheme (strains x N levels x phenological stage), at two contrasting nitrogen levels: low and high nitrogen. The plants were evaluated at five growth stages: stage nine (V9), with 14 fully-developed leaves (V14), tasseling (VT), flowering (R1) and physiological maturity (R6). The following characteristics were evaluated: efficiency in the usage, absorption, use and translocation of nitrogen; activity of nitrate reductase and glutamine synthetase; length of the lateral and axial roots; specific root area; chlorophyll content; number of leaves; plant height; stem diameter; and the levels of phosphorus and potassium. Considering the estimated direct and indirect gains, it can be concluded that the activities of glutamine synthetase at the V9 and V14 stages permit early indirect selection for nitrogen use efficiency in maize under conditions of low and high N availability respectively. RESUMO -Vários trabalhos de avaliação de eficiência no uso de nitrogênio (EUN) já foram feitos utilizando estádios precoces. Contudo, não há relatos científicos sobre o estádio ideal e, neste, quais caracteres que apresentam maior correlação com a EUN. Assim, o objetivo foi identificar os estádios fenológicos e os caracteres secundários que maximizam a acurácia na seleção precoce e indireta para a EUN em milho. Para isso, foram avaliadas três linhagens endogâmicas de milho em delineamento inteiramente casualizado, com cinco repetições, em esquema fatorial triplo (linhagens x níveis de N x estádio fenológico), em duas doses contrastantes de nitrogênio -baixo e alto nitrogênio. As plantas foram avaliadas em cinco estádios fenológicos sendo eles: nove (V9) e 14 folhas completamente desenvolvidas (V14), pendoamento (VT), florescimento (R1) e maturidade fisiológica (R6). Foram avaliados os caracteres: eficiência na utilização, na absorção, no uso e na translocação de nitrogênio, atividade da nitrato redutase e da glutamina sintetase, comprimento de raiz lateral e axial, área de raiz específica, teor de clorofila, número de folhas, altura de planta, diâmetro de colmo, teor de fósforo e potássio. Considerando os ganhos diretos e indiretos estimados, conclui-se que as atividades da glutamina sintetase, nos estádios V9 e V14, permitem a seleção precoce e indireta para eficiência no uso de nitrogênio em milho, nas condições de baixa e alta disponibilidade de N, respectivamente.Palavras-chave: Zea mays. Análise de trilha. Estresse abiótico. Melhoramento vegetal.

Evaluation of Efficiency and Response of Quinoa Plant to Nitrogen Fertilization levels

“…These results are consistent with the findings of other researchers who emphasized that increasing N application does not necessarily increase NUE (Meyers, 1998;Schulte et al, 2005;Pospišil et al, 2006;Abou-Amer and Kamel, 2011;Kakabouki et al, 2018). Many investigations have proposed that there are numerous environmental, agronomic and genetic factors that affect NUE (Benincasa et al, 2011;MacDonald et al, 2013;Caixeta et al, 2015;Stahl et al, 2017), which in summary is a function of plant potential to uptake or acquisition N from the soil and its ability to physiologically utilize the absorbed N (Pathak et al, 2011). Kakabouki et al (2018) concluded that quinoa plants are highly competent in absorbing soil N; however, they appear poor in remobilizing N from the vegetative parts into the seeds under high N supply.…”