Root Morphology of Maize and Its Relationship to Root Lodging

Abstract Crown root traits of maize ( Zea mays L.) such as number and diameter are the most easily accessible root traits. Their impact on root lodging resistance is little documented. We evaluated 28 flint x dent hybrids at one location for 2 years for crown root traits and for lengths of internodes. Plants were grown at normal and at supraoptimal density. A maximum number of crown roots was observed at the fifth and sixth nodes, above ground internodes 8‐10 had maximum lengths. After a cool wet year maximum internode length or numbers of roots per node were found at higher tiers. A supraoptimal plant density caused an increase in lengths and a decrease in root numbers at upper internode and node levels. Crown root morphology and histology were studied at normal plant density in one growing season. From the lowest to the highest node level, root diameters increased steadily, whereas the number of late (large) metaxylem vessels in crown roots showed a strong increase at upper nodes. The diameters of metaxylem vessels increased already strongly at lower node tiers. All data were correlated with the root lodging counts from 42 hybrid tests in northern and southern Germany. In the warm year, at normal plant density, length of internodes 6 and 8 were correlated significantly positively with root lodging in about 25 % of all cases. Number of metaxylem vessels in roots at node 6 were significantly negatively correlated with root lodging in more than 20 % of all cases. Specific morphological and histological traits seem to indicate root lodging. However, their expression depends to a great extent on environment which lessens their value for selection.