Nitrogen Use Efficiency among Diverse Sorghum Cultivars

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Abstract
Genetic diversity for N use efficiency (NUE) has been demonstrated in sorghum [Sorghum bicolor (L.) Moench] with some of the most efficient types being cultivars that evolved from low‐fertility environments. The objectives of this study were to compare diverse sorghum cultivars for their ability to cope with limited supplies of N. A Nigerian landrace (SC566), an Indian improved line (M35‐1), two U.S. pure lines (CK60 and Martin), and a commercial sorghum hybrid (Dekaib E59 4‐) were compared in solution culture and under two levels of limited N availability in a Nebraska field environment. Dry matter production and NUE (grants of dry matter per gram of N) were determined among all environments. In the field environments, the vertical canopy profile was divided into three layers and repeated observations were made of leaf morphology, internal leaf anatomy, N content, and CO2 gas exchange rates under light saturating and dark conditions. As the nature of N stress changed and increased among environments, SC566 and M35‐1 becmne superior to all U.S. cultivars in NUE. Conversely, U.S. cultivars were among the most responsive in total dry matter production and grain yield as N supply increased. In general, traits related to high NUE included larger canopies comprised of fewer but larger leaves with low N concentration, thicker leaves, larger leaf phloem transsectional area, rapid solubilization and remobilization of N from older to younger leaves, and lower dark respiration rates. These cluwacteristics did not necessarily seem related to the level of domestication or origin of a cultivar, though M35‐1 was found superior in NUE among all environments. Unique and possibly useful traits were found among both landrace and domesticated cultivars.

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