Pre-harvest stress cracks in maize (Zea mays L.) kernels as characterized by visual, X-ray and low temperature scanning electron microscopical analysis: effect on kernel quality

Internal cracks caused by high temperature or excessive moisture during mai ze (Zea mays L.) kernel development were characterized, and their effects o n kernel quality were assessed. Pre-harvest stress cracks are often located near the middle of the kernel along the embryo axis, but they were also de tected in other positions, irrespective of the shape of the kernel. X-ray a nalysis enabled visualisation of stress cracks that are invisible to the hu man eye and, therefore, gave a better estimate of the percentage of cracks. However, low temperature scanning electron microscopy of the surface of mi lled kernels revealed small cracks not noticed by visual or X-ray inspectio n. All kernels tested in this way had a crack of some sort in the endosperm tissue. Cracks were also frequent in the scutellum, but rare in the embryo axis. Endosperm cracks followed the boundary of the starch granules, but d id not extend into the pericarp tissue. In contrast to external cracks caus ed by mechanical impact, preharvest internal stress cracks generally are no t detrimental to germination and vigour. However, if the crack is located i nside or perpendicular to the embryo axis, it may affect the quality of the kernel, probably by impeding nutrient translocation to the embryo.