Abstract Abstract: The formononetin biostimulant may be an option for reducing P fertilization once it stimulates mycelial growth of arbuscular mycorrhizal fungi and increases plant ability to take up nutrients through the roots, especially phosphorus. The objective of this study was to evaluate the effect of formononetin associated with phosphorus fertilization in maize. Field experiments were conducted in a randomized block design with a 3 × 4 factorial arrangement (0, 50 or 70, and 140 kg ha-1 P2O5; and formononetin application rates: 0, 25, 50, and 100 g ha-1), with four replications. Formononetin (100 g ha-1) increased the mycorrhizal colonization rate up to 30% in maize in the first four weeks after emergence when no P fertilizer was applied, and to 17% when 50 or 70 kg ha-1 of P2O5 were applied. The application of 50 and 100 g ha-1 of formononetin significantly increased plant height, ear height, and grain yield (22% - 76%) when no P fertilizer was applied. The use of formononetin in the field stimulates mycorrhizal colonization, has a positive effect on maize yield, and reduces the need for P fertilizer application in maize. However, this effect was evident only at low P soil contents.

O objetivo desse trabalho foi avaliar o nível de resistência de 12 híbridos comerciais de milho à cercosporiose, causada por Cercospora zeae-maydis, e à Mancha Branca, causada por Pantoea ananatis e comparar a eficiência das estimativas da área abaixo da curva de progresso das doenças e da estabilidade fenotípica, na avaliação da resistência a esses patógenos. Foram conduzidos três experimentos, no ano agrícola de 2007/2008, em três locais. Utilizou-se o delineamento em blocos ao acaso com três repetições. Foram realizadas cinco avaliações da severidade das doenças, em intervalos de sete dias, a partir dos 80 dias da emergência, por meio de uma escala de notas variando de 1 (altamente resistente) a 9 (altamente suscetível). Foram estimadas a área abaixo da curva de progresso da doença (AACPD) e o coeficiente de regressão linear (b1) entre a variável independente época de avaliação (x) e a variável dependente severidade da doença (y) e o coeficiente de determinação (R²). Observou-se que, ambas as metodologias utilizadas mostraram-se eficientes na discriminação do nível de resistência dos híbridos avaliados à Cercosporiose e à Mancha Branca, permitindo a classificação de modo semelhante. Os híbridos mais resistentes às duas doenças foram o AG7088, AG7010 e 2B707 e os mais suscetíveis o 30F44, 30F53 e AG8021. Os híbridos 30K64, DKB177, DKB390 e Impacto apresentaram comportamento variável em função dos locais de avaliação.

With the objective of evaluating the resistance level of commercial corn hybrids and comparing the efficiency of the estimates of the area under the disease progress curve (AUDPC) and that of the phenotypical stability parameters in the evaluation of resistance maize white spot and gray leaf spot, three experiments were carried out in the agricultural year of 2007/2008 in three environments. Twelve commercial maize hybrids were used, in a randomized block experimental design with three replications. Five evaluations of disease severity (maize white spot and gray leaf spot) based on visual symptoms were performed at seven-day intervals from the 80th day after maize emergence, ranging from 1 (highly resistant) to 9 (highly susceptible). The area under the disease progress curve (AUDPC) was estimated, as were the phenotypical stability parameters, i.e., the linear regression coefficient (b i) between the independent variable evaluation time (x), and the dependent variable, disease severity (y) and the determination coefficient (R²). It was found that in the case of maize white spot and maize gray leaf spot, both methodologies used proved to be effective in the discrimination of the resistance level of the hybrids, enabling them to be ranked in a similar way. The most resistant hybrids to maize white spot and maize gray leaf spot were AG7088, AG 7010 and 2B707, and the most susceptible were 30F44, 30F53 and AG8021. The 30K64, DKB177, DKB390 and Impacto hybrids showed variable levels of resistance with the environment.