American Journal of Plant Sciences
Vol.3 No.10(2012), Article ID:24030,4 pages DOI:10.4236/ajps.2012.310162

Effect of Planting Density, Irrigation Regimes, and Maize Hybrids with Varying Ear Size on Yield, and Aflatoxin and Fumonisin Contamination Levels

Hamed K. Abbas1*, Henry J. Mascagni Jr.2, H. Arnold Bruns3, W. Thomas Shier4, Kenneth E. Damann5

1United States Department of Agriculture-Agricultural Research Service, Biological Control of Pests Research Unit, Stoneville, USA; 2Northeast Research Center, Louisiana State University AgCenter, St. Joseph, USA; 3United States Department of Agriculture-Agricultural Research Service, Crop Production Systems Research Unit, Stoneville, USA; 4Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota, Minneapolis, USA; 5Department of Plant Pathology & Crop Physiology, Louisiana State University AgCenter, Baton Rouge, USA.

Email: *Hamed.Abbas@ars.usda.gov

Received August 31st, 2012; revised September 28th, 2012; accepted October 5th, 2012

Keywords: Aflatoxin; Fumonisin; Mycotoxin; Corn; Maize; Environmental Manipulation; Irrigation; Flexible Kernel Number Trait

ABSTRACT

Corn (maize, Zea mays L.) hybrids expressing the flexibility trait in ear size (number of kernels per ear) are marketed for ability to give higher yields under adverse conditions. Altered kernel number is associated with altered number of silk, a major route for infection of kernels by aflatoxin-producing fungi such as Aspergillus flavus. The effect of plant density and irrigation level on yield and accumulation of aflatoxins and fumonisins in harvested grain was compared in a fixed-ear hybrid (Pioneer 33K81), a semi-flexible ear hybrid (Pioneer 3223) and a flexible ear hybrid (Golden Acres 8460) over a range of seeding densities (49,400, 61,750, 74,700, 86,450, and 98,800 seeds·ha1) in non-irrigated, moderately-irrigated (6.4 cm soil water deficit) and well-irrigated plots (3.8 cm soil water deficit), during three years with variable rainfall. Irrigation increased yields in all hybrids, but in the absence of irrigation, yields were highest with the semi-flexible ear trait hybrid. In general, the hybrid with the flexible ear trait had lower optimal seeding densities than the other hybrids for each soil water regime. In general, kernel number was least affected by seeding density in the hybrid with fixed-ear trait compared to the semiand flexible ear hybrids. The lowest levels of aflatoxin and of fumonisin contamination in harvested grain were associated with the flexible ear trait at all rainfall and irrigation levels, but there was no evidence that reducing stress by lowering seeding density reduced mycotoxin contamination. Inoculation with A. flavus resulted in much higher levels of aflatoxin and significantly higher levels of fumonisin contamination in grain of all hybrids under most conditions of rainfall and irrigation, suggesting that factors that promote A. flavus infection can affect production of both mycotoxins.

1. Introduction

Contamination by aflatoxin is a major determinant of crop quality in corn (maize, Zea mays L.) in the US, particularly in the Southern US, where the hot, dry conditions which favor Aspergillus flavus and other aflatoxin-producing fungi frequently occur [1-7]. Fungi cause a variety of root, stalk and ear rots in corn, all of which cause some loss of yield, but it is aflatoxin produced by Aspergillus flavus contaminating kernels that is responsible for the greatest economic losses [8]. Aspergillus flavus spores infect corn after over-wintering in reservoirs provided by the soil and surface plant debris. The husk on the ear constitutes a major physical barrier to infection of kernels by A. flavus, but between silking (reproductive stage R1) and blacklayer (physiological maturity, reproductive stage R6) [9], the silks provide avenues for A. flavus to enter the ear and infect the kernels. The fungus may also infect the kernels by entering through exposed kernels, i.e. insect dammes, 2003.

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  • NOTES

    *Corresponding author.