Use of molecular markers to evaluate rice genetic variation in associative N2 fixation, N uptake, and N use efficiency.
1994
Wu P. | Ladha J.K. | McCouch S.R. | Teng S.B.
Significant differences among rice varieties in associative N2 fixation, N uptake, and N use efficiency (NUE) have been found over the last 10 yr. Three methods were used: N balance (a measure of the plant's ability to exploit soil N), acetylene reduction, and 15 N dilution (both measures of N2 fixation). The advantages and limitations of these methods for varietal screening are outlined together with a summary of work over the past decade. It was found that IR42 consistently had high N2 fixation and N balance and performed well in soils with low N fertility. Palawan, a local variety, had low N2 fixation and N balance. In 15N dilution experiments in a greenhouse and the field, IR42 and Palawan showed significant differences in associative biological N2 fixation, N uptake, and NUE. There was roughly a 20 percent difference in atom percent 15N excess between IR42 and Palawan. There were strong correlations between atom percent 15N excess and the chlorophyll content of the flag leaf, between N uptake and yield, and between NUE and yield. In a primary restriction fragment length polymorphism (RFLP) survey comprising 11 genotypes with 4 enzymes and 44 probes, 65 percent polymorphism was found between IR42 and Palawan. Based on the survey results, 120 polymorphic probes were selected throughout the 12 chromosomes for tagging genes underlying the traits identified in a parental survey with 180 probes with 6 enzymes (EcoR5, Sca1, Hind3, Xba1 and Dra1). The enzymes of XbaI and DraI performed well in detecting polymorphisms between the test genotypes; the enzyme of Hind3, Sca1, and EcoR5 were superior to EcoR1.
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