Potential for nitrogen fixation in maize genotypes in Brazil.

Area of Science:

• Agricultural Science
• Microbiology
• Plant Physiology

Background:

• Nitrogen (N(2)) fixation is crucial for plant growth, but typically associated with legumes.
• Maize (Zea mays L.) is a staple crop with high nitrogen demands.
• Understanding non-legume nitrogen fixation can improve sustainable agriculture.

Purpose of the Study:

• To estimate nitrogen (N(2)) fixation in field-grown maize using a nondestructive method.
• To screen maize lines for variations in nitrogenase activity.
• To identify potential microbial contributors to nitrogen fixation in maize roots.

Main Methods:

• Employed a nondestructive acetylene reduction assay to measure nitrogenase activity in field-grown maize.
• Screened 276 S(1) maize lines, selecting 17 for further nitrogenase assays.
• Isolated N(2)-fixing Spirillum sp. from maize root pieces.

Main Results:

• Nitrogenase activities varied significantly among maize lines, with some exceeding the original cultivar by over 20-fold.
• The highest observed nitrogenase activity approached that of soybean, a known N(2) fixer.
• Maximum nitrogenase activity in brachytic maize occurred around the 75% silking stage.
• Soil conditions significantly influenced nitrogenase activity.
• N(2)-fixing Spirillum sp. were identified as the likely source of root nitrogenase activity.

Conclusions:

• Field-grown maize exhibits measurable nitrogen (N(2)) fixation, primarily mediated by root-associated Spirillum sp.
• Significant genotypic variation exists for nitrogenase activity in maize, suggesting potential for breeding programs.
• N(2) fixation in maize, if optimized, could contribute substantially to crop nitrogen requirements, reducing fertilizer dependency.