Department of Agricultural Research and Diagnosis - DDPA, Secretary of Agriculture, Livestock, and Rural Development of Rio Grande do Sul - SEAPDR, 570 Gonçalves Dias St, 90130-060, Porto Alegre, Rio Grande do Sul, Brazil.
La Salle University - Unilasalle, 2288 Vitor Barreto Ave, 92010-000, Canoas, Rio Grande do Sul, Brazil.
Braz J Microbiol. 2023 Mar;54(1):335-348. doi: 10.1007/s42770-022-00867-2. Epub 2022 Nov 11.
Black wattle (Acacia mearnsii) is a forest species of significant economic importance in southern Brazil; as a legume, it forms symbiotic associations with rhizobia, fixing atmospheric nitrogen. Nonetheless, little is known about native rhizobia in soils where the species is cultivated. Therefore, this study aimed to evaluate the diversity and symbiotic efficiency of rhizobia nodulating A. mearnsii in commercial planting areas and validate the efficiency of a potential strain in promoting seedling development. To this end, nodules were collected from four A. mearnsii commercial plantations located in Rio Grande do Sul State, southern Brazil. A total of 80 rhizobia isolates were obtained from black wattle nodules, and thirteen clusters were obtained by rep-PCR. Higher genetic diversity was found within the rhizobial populations from the Duas Figueiras (H' = 2.224) and Seival (H' = 2.112) plantations. Twelve isolates were evaluated belonging to the genus Bradyrhizobium, especially to the species Bradyrhizobium guangdongense. The principal component analysis indicated an association between rhizobia diversity and the content of clay, Ca, Mg, and K. Isolates and reference strains (SEMIA 6163 and 6164) induced nodulation and fixed N via symbiosis with black wattle plants after 60 days of germination. The isolates DF2.4, DF2.3, DF3.3, SEMIA 6164, SEMIA 6163, CA4.3, OV3.4, and OV1.4 showed shoot nitrogen accumulation values similar to the N + control treatment. In the second experiment (under nursery conditions), inoculation with the reference strain SEMIA 6164 generally improved the growth of A. mearnsii seedlings, reinforcing its efficiency even under production conditions.
黑荆树（Acacia mearnsii）是巴西南部具有重要经济意义的森林物种；作为豆科植物，它与根瘤菌形成共生关系，固定大气氮。然而，对于在该物种种植的土壤中存在的本地根瘤菌却知之甚少。因此，本研究旨在评估在商业种植区中与 A. mearnsii 共生的根瘤菌的多样性和共生效率，并验证一种潜在菌株在促进幼苗生长方面的效率。为此，从巴西南部南里奥格兰德州的四个 A. mearnsii 商业种植园中收集了根瘤。从黑荆树的根瘤中获得了 80 个根瘤菌分离株，并通过重复 PCR 获得了 13 个聚类。在 Duas Figueiras（H' = 2.224）和 Seival（H' = 2.112）种植园的根瘤菌群中发现了更高的遗传多样性。12 个分离株被评估属于慢生根瘤菌属，特别是 Bradyrhizobium guangdongense 种。主成分分析表明，根瘤菌多样性与粘土、Ca、Mg 和 K 的含量之间存在关联。分离株和参考菌株（SEMIA 6163 和 6164）在种子发芽 60 天后通过与黑荆树植物共生诱导结瘤并固定氮。分离株 DF2.4、DF2.3、DF3.3、SEMIA 6164、SEMIA 6163、CA4.3、OV3.4 和 OV1.4 的茎氮积累值与 N+对照处理相似。在第二个实验（在苗圃条件下）中，参考菌株 SEMIA 6164 的接种通常会改善 A. mearnsii 幼苗的生长，即使在生产条件下也能增强其效率。
