Author
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Harper, James |
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Submitted to: Biennial Conference on Molecular and Cellular Biology of the Soybean
Publication Type: Abstract Only Publication Acceptance Date: 7/29/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Nonnodulating and partially-nitrate-tolerant hypernodulating soybean mutants have been isolated and have been useful as experimental tools in assessing nodulation control. Two genes (rj5 and rj6) have been shown to control the nonnodulation trait, and one gene (rj7) controls hypernodulation/supernodulation mutants of Bragg, Williams, and Enrei. The control of the nonnodulating characteristic is at an early stage of infection and involves lack of root hair curling. Hypernodulation expression appears to be due to loss of the normal autoregulatory control of nodulation expressed in typical soybean cultivars. It is known that a shoot-transmissible signal controls expression of hypernodulation, and although the specific signal has not been identified it appears to be common among soybean, mung bean, and dolichos, based on grafting studies. The apparent linkage of hypernodulation expression with depressed root growth has limited progress in selecting hypernodulated lines with good agronomic performance. The depressed root growth is not due solely to excess nodulation in that root growth is inferior on the hypernodulated lines even in the absence of inoculation. Our results with the four hypernodulating mutant (NOD) lines, including advanced backcross generations, indicates that agronomic yield is inferior to that of the original parent Williams; maximum yield of the best backcross lines are about 90% of the Williams parent. The advantage of hypernodulated mutants may be manifested in subsequent crops grown in rotation with soybean, rather than to any direct benefit to the soybean crop. Identification of the shoot-derived signal which provides autoregulatory control of nodule number remains a major goal. |
