Anatomy of Seedling Roots of Tropical Maize (Zea mays L.) Cultivars at Low Water Supply

摘要

Establishment of maize seedlings can be difficult at low soil moisture content. Anatomy of root metaxylem vessels may influence the capacity for water transport and respective genotypic differences might be useful for selection purposes. To test this, six tropical maize (Zea mays L.) cultivars were grown in large PVC tubes containing a sandy substrate at 5% (M5) and 10% (M10) moisture contents for 2 weeks. The percentage changes in root diameters due to M5 was similar for most cultivars but differed for main root types. Root diameters were not consistently related to metaxylem structure, but in a few cases, thin roots had smaller diameter metaxylem vessels. The M5 treatment reduced the number of late metaxylem vessels of primary roots by about 0 to 20%, while effects on nodal roots were slight. Generally, the ratio of cross-sectional areas between late and early metaxylem vessels increased from primary to seminal and nodal roots. Within the cultivar Tuxpefio this ratio was much reduced by M5. A few cultivars maintained the combined cross-sectional areas of metaxylem vessels at M5 in some main root types, but only one cultivar could achieve this for the total of cross-sectional areas of metaxylem vessels, calculated over all root axes, by increasing the number of seminal and nodal roots. These anatomical traits seemed to be mostly constitutive with limited response to an actual environment, but they could be decisive for the suitability of a cultivar to an environment with frequent water shortages during seedling establishment