Alfalfa (Medicago sativa L.) and Sinorhizobium meliloti: Prospects of using rhizobial inoculants in Serbia

Abstract

© 2016 Institute of Botany and Botanical Garden Jevremovac, Belgrade. It is considered that the symbiotic association between alfalfa (Medicago sativa L.) and Sinorhizobiummeliloti is one of the most efficient interactions between N2-fixing bacteria and legumes. But evengreater efficiency of symbiotic nitrogen fixation can be achieved by selecting the best combinationsof host genotypes and nodule bacteria. The Serbian K-28 cultivar has the potential capacity tobe a good parental genotype in breeding programs for improved N2 fixation capability throughinoculation with particular compatible strains. On the other hand, S. meliloti strain L5 is a broadlyeffective inoculant with most alfalfa cultivars, with a mean value of fixed N2 of 35% over a twoyearperiod. Serbian soils are well supplied with autochthonous rhizobial strains which specificallynodulate alfalfa, and this is why the use of rhizobial inoculants in alfalfa production in Serbia is nota common practice. However, the number and effectiveness of such strains depend on soil type,the land use system (alfalfa stand, arable land and lea) and the alfalfa host plant. For this reason,use of rhizobial inoculants with highly effective strains is needed in alfalfa production. Our twoyearfield experiment showed that shoot dry weight increased by 42-77% in inoculated alfalfa,while the amount of fixed nitrogen increased by 35%. Alfalfa inoculation with effective strains isan alternative approach to improving the long-term productivity of alfalfa. In our five-year trial,the inoculated K-28 alfalfa cultivar showed maximum nitrogen fixation (293 kg N ha-1) in thefourth year of utilisation. During this period, symbiotic nitrogen fixation of alfalfa, determinedfrom fixed N2 in the second cutting, varied between 32 and 44%. The most effective strain promotedan increase of shoot dry weight by 34-60% in relation to the control in the third and fourth years ofutilisation. In addition, Sinorhizobium spp. have the potential to be used as plant growth-promotingrhizobacteria (PGPR). Inoculation of Italian ryegrass seeds with a particular rhizobial strain theyear before alfalfa growing ensured abundant nodulation and better growth of the alfalfa. In Serbiathere are rhizobial inoculants of alfalfa with consistently high quality which permit reductionof mineral N fertiliser use in production of this crop, with consequent economic and ecologicalbenefits.