Robleto EA, Kmiecik K, Oplinger ES, Nienhuis J, Triplett EW
Department of Agronomy, University of WisconsinMadison, Madison, Wisconsin 53706.
Appl Environ Microbiol. 1998 Jul 1;64(7):2630-3. doi: 10.1128/AEM.64.7.2630-2633.1998.
A major barrier to the use of nitrogen-fixing inoculum strains for the enhancement of legume productivity is the inability of commercially available strains to compete with indigenous rhizobia for nodule formation. Despite extensive research on nodulation competitiveness, there are no examples of field efficacy studies of strains that have been genetically improved for nodulation competitiveness. We have shown previously that production of the peptide antibiotic trifolitoxin (TFX) by Rhizobium etli results in significantly increased nodule occupancy values in nonsterile soil in growth chamber experiments (E. A. Robleto, A. J. Scupham, and E. W. Triplett, Mol. Plant-Microbe Interact. 10:228-233, 1997). To determine whether TFX production by Rhizobium etli increases nodulation competitiveness in field-grown plants, seeds of Phaseolus vulgaris were inoculated with mixtures of Rhizobium etli strains at different ratios. The three nearly isogenic inoculum strains used included TFX-producing and non-TFX-producing strains, as well as a TFX-sensitive reference strain. Data was obtained over 2 years for nodule occupancy and over 3 years for assessment of the effect of the TFX production phenotype on grain yield. In comparable mixtures in which the test strain accounted for between 5 and 50% of the inoculum, the TFX-producing strain exhibited at least 20% greater nodule occupancy than the non-TFX-producing strain in both years. The TFX production phenotype had no effect on grain yield over 3 years; the average yields reached 2,400 kg/ha. These results show that addition of the TFX production phenotype significantly increases nodule occupancy under field conditions without adverse effects on grain yield. As we used common inoculation methods in this work, there are no practical barriers to the commercial adoption of the TFX system for agriculture.
使用固氮接种菌株提高豆科植物生产力的一个主要障碍是，市售菌株无法与本地根瘤菌竞争形成根瘤。尽管对根瘤形成竞争力进行了广泛研究，但尚无经基因改良提高根瘤形成竞争力的菌株进行田间功效研究的实例。我们之前已经表明，在生长室实验中，菜豆根瘤菌产生的肽抗生素三叶毒素（TFX）可显著提高非无菌土壤中的根瘤占据值（E. A. 罗布莱托、A. J. 斯库法姆和E. W. 特里普利特，《分子植物 - 微生物相互作用》10:228 - 233，1997年）。为了确定菜豆根瘤菌产生TFX是否能提高田间种植植物的根瘤形成竞争力，用不同比例的菜豆根瘤菌菌株混合物接种菜豆种子。使用的三种近等基因接种菌株包括产生TFX的菌株、不产生TFX的菌株以及对TFX敏感的参考菌株。获取了两年的根瘤占据数据以及三年的TFX产生表型对籽粒产量影响的评估数据。在测试菌株占接种物5%至50%的可比混合物中，两年内产生TFX的菌株的根瘤占据率均比不产生TFX的菌株至少高2０%。TFX产生表型在三年中对籽粒产量没有影响；平均产量达到2400千克/公顷。这些结果表明，添加TFX产生表型可在田间条件下显著提高根瘤占据率，且对籽粒产量无不利影响。由于我们在这项工作中使用了常规接种方法,TFX系统在农业上的商业应用没有实际障碍。
