Legume Genomics and Genetics 2024, Vol.15, No.3, 140-151 http://cropscipublisher.com/index.php/lgg 147 6 Case Studies and Field Trials 6.1 Success stories in different legume species Soybeans have shown significant improvements in growth and yield when inoculated with specific strains of Rhizobium. For instance, a study demonstrated that co-inoculation with Rhizobiumsp. SL42 and Bradyrhizobium japonicum532C (Bj) resulted in higher shoot biomass and increased seed weight under salt stress conditions. This treatment improved grain yield by 7.4% and 8.1% under optimal conditions with Bj+SL48 and Bj+SL42+SL48 treatments, respectively (Ilangumaran et al., 2021). Another study highlighted that Rhizobiuminoculation reduced the need for phosphorus and potassium fertilization in soybean-maize intercropping systems, enhancing nutrient uptake and overall plant health (Nyoki and Ndakidemi, 2018). Chickpeas have also benefited fromRhizobiuminoculation. In Spain, the co-inoculation of Mesorhizobium ciceri C-2/2 and Pseudomonas jessenii PS06 significantly increased seed yield by 52% compared to the control. This synergistic effect was particularly notable under field conditions, where the co-inoculation treatment also resulted in higher nodule fresh weight and shoot nitrogen content (Valverde et al., 2006). Lentils have shown improved nodulation and plant growth when inoculated with pre-induced Rhizobium leguminosarum. The use of specific flavonoids like hesperetin and naringenin to pre-activate nod genes resulted in a significant increase in nodule number and dry matter accumulation in lentil plants (Begum et al., 2001; Igiehon et al., 2020). Additionally, Rhizobiumsp. strain MRL3, which is tolerant to insecticides, improved the growth and yield of lentils in insecticide-stressed soils, demonstrating its potential as a bioinoculant (Ahemad and Khan, 2011; Buernor et al., 2022). 6.2 Experimental data from recent trials Recent trials have employed various methodologies to assess the impact of Rhizobium inoculation on legume crops. For example, a field experiment in Ghana used a randomized complete block design to evaluate the effectiveness of different Rhizobium inoculants on soybean and cowpea. The results showed significant increases in nodule number, nodule dry weight, and grain yield for both crops when inoculated with specific strains like Biofix and BR 3 267 (Ulzen et al., 2016). Another study conducted greenhouse and field experiments to test the effects of single and dual inoculations on chickpea growth, finding that co-inoculation with Mesorhizobium ciceri C-2/2 and Pseudomonas jessenii PS06 yielded the highest seed yield and nodule fresh weight under field conditions (Valverde et al., 2006). The impact of Rhizobiuminoculation on yield and soil health has been profound. In soybeans, inoculation with Rhizobium sp. SL42 and Bradyrhizobium japonicum 532C not only increased grain yield but also improved nitrogen assimilation and the shoot K+/Na+ ratio, indicating enhanced stress tolerance and soil health (Ilangumaran et al., 2021). In chickpeas, the co-inoculation with Mesorhizobium ciceri C-2/2 and Pseudomonas jessenii PS06 led to higher nodule fresh weight and shoot nitrogen content, contributing to better soil fertility (Valverde et al., 2006). Similarly, in lentils, the use of insecticide-tolerant Rhizobiumsp. strain MRL3 improved plant growth and yield in insecticide-stressed soils, suggesting a positive impact on soil microbial diversity and health (Ahemad and Khan, 2011). By integrating these findings, it is evident that Rhizobiuminoculation plays a crucial role in enhancing legume crop performance and soil health, making it a valuable practice for sustainable agriculture. 7 Challenges and Future Directions 7.1 Overcoming biological and technical barriers One of the primary challenges in utilizing Rhizobiumfor legume crop enhancement is the host range limitation. The specificity of rhizobium-legume symbiosis means that certain rhizobium strains can only nodulate specific legume species, which restricts the broader application of effective strains. For instance, the study on Rhizobium leguminosarumbiovar viciae demonstrated that only 34% of isolates could nodulate Vicia faba, while 89% could nodulate local wild hosts, indicating a significant host range limitation (Mutch and Young, 2004). Additionally, the genetic diversity and specificity of Rhizobium strains further complicate the development of universal inoculants (Lemaire et al., 2015).
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