Methods to classify maize cultivars in use efficiency and response to nitrogen

Abstract

RESUMO Métodos para classificar cultivares de milho em eficiência no uso e na resposta ao nitrogênioNos programas de melhoramento de plantas que têm como objetivo obtenção de cultivares mais eficientes e responsivos à quantidade de nitrogênio (N), há interesse em métodos seletivos que sejam de baixo custo, rápida resposta, alta repetibilidade e aplicáveis em grande número de cultivares. Assim, os objetivos deste trabalho foram avaliar técnicas experimentais de campo aplicáveis à rotina de programas de melhoramento para classificar cultivares de milho eficientes e responsivos ao N. Foi realizado um experimento em delineamento de blocos casualizados, e os tratamentos foram arranjados em parcela subdividida com três repetições e cinco doses de N (0, 30, 60, 120 e 200 kg ha -1 ) em parcelas e seis cultivares de milho em subparcelas. Foram comparados os métodos de eficiência e resposta (ER) com duas doses contrastantes de N, a análise de variância com teste de média e a análise de regressão. Concluiu-se que o método da eficiência no uso e na resposta com base nas duas doses mais contrastantes de N classifica os cultivares Received: 10/01/2011; Accepted: 30/07/2013 n plant breeding programs that aim to obtain cultivars with nitrogen (N) use efficiency, the focus is on methods of selection and experimental procedures that present low cost, fast response, high repeatability, and can be applied to a large number of cultivars. Thus, the objectives of this study were to classify maize cultivars regarding their use efficiency and response to N in a breeding program, and to validate the methodology with contrasting doses of the nutrient. The experimental design was a randomized block with the treatments arranged in a split-plot scheme with three replicates and five N doses (0, 30, 60, 120 and 200 kg ha -1 ) in the plots, and six cultivars in subplots. We compared a method examining the efficiency and response (ER) with two contrasting doses of N. After that, the analysis of variance, mean comparison and regression analysis were performed. In conclusion, the method of the use efficiency and response based on two N levels classifies the cultivars in the same way as the regression analysis, and it is appropriate in plant breeding routine. Thus, it is necessary to identify the levels of N required to discriminate maize cultivars in conditions of low and high N availability in plant breeding programs that aim to obtain efficient and responsive cultivars. Moreover, the analysis of the interaction genotype x environment at experiments with contrasting doses is always required, even when the interaction is not significant.

Strategy in the selection of corn genotypes for their efficiency and response to nitrogen

“…The latter indicates a differential behavior of the genotypes at different levels of fertilization. The coefficient of variation (CV) was from 7,5%, less than those found by Godoy et al (2013), and Cancellier et al (2011). This CV indicates good accuracy in the conduction of the experiments, is considered low because it is less than 10% according to the classification proposed by Pimentel-Gomes (2009).…”

Phenotypic and Genetic Parameters Estimated for Fresh Corn Under Different Nutrient Availability1

“…The lowest rate, or critical level for breeding programs focused on tolerance to abiotic stresses and N and P use efficiency, should be determined to select cultivars more adapted to these environments, because the trait heritability decreases as the as stress is increased, which decreases the variability and make the recurrent selection process unfeasible. Godoy et al (2013) reported that the N rate of 60 kg ha -1 is an adequate critical level to classify corn genotypes; however, after a low number of cycles, the variability tends to be exhausted, as found for N; and that this rate generates almost no variability to continue the program (Table 4). Woli et al (2016) reported that grain yield and N use efficiency in hybrids increased from 1960 top 2000, but not during the 1980s and 1990s, and the ability of plant to absorb nitrogen presented a slightly increase during this period.…”