The formation of rhizobium nodulation is a key symbiotic mechanism in legume crops for their adaptation to marginal environments. The quantitative assessment of their impact on plant growth and economic yields is crucial for cultivar improvement and optimizing agricultural productivity. In this study, the selected parents are landraces, distinguishing one as a non-nodulating mutant (ICC 4918NN) derived from the other germplasm (ICC 4918). By employing the RGA approach, we successfully generated a RIL population within a mere 18 months, a testament to the efficiency and robustness of the methodology utilized66. While the potential of RGA has been acknowledged in other crops such as pea61, pigeon pea69, barley and wheat81, and canola81, its application in practical breeding programs remains largely unexplored. The variance analysis revealed a significant difference (P < 0.01) among the RILs for all the traits under the study. This indicates the presence of ample variability for the traits in the population (Table 1). Significant genetic variability among genotypes was observed in earlier studies evaluated for nodulation-related traits in chickpea31,32.
A notable finding in our study is the substantial increase in yield (62.55%) in NG compared to NNG. The improvement was majorly contributed by the increase in the NPPP (39.5%) and NSPP (44.4%). On a moderate level, nodulation has reduced the flowering time and maturity and enhanced the PH, SBr, SW100 and HI (Table 1). These results indicate that NGs were more efficient in synthesizing photosynthates, which led to produce more number of flowers for generating a large number of pods and seeds46,71 than NNG. In addition, the yield advantage reflects not only the inherent genetic potential of the legume plant but also the synergistic effects of the established symbiosis between roots and rhizobial bacteria. The result agrees with an earlier study in chickpea, which reported a 31% higher yield in NG compared to NNG counterparts63,64. The current study, with a more pronounced yield advantage, emphasizes the significance of rhizobial nodulation in optimizing chickpea productivity.
The poorer performance of NNG may be attributed to the deficiency of nitrogen fixation through nodulation, emphasizing its crucial role in chickpea productivity. The reliance on alternative nitrogen sources becomes crucial for NNG genotypes, and supplementing nitrogen in the form of fertilizers may be necessary to enhance yield41. This aligns with previous findings in chickpea and groundnut, where NNGs in nitrogen-rich soils could attain yields on par with NG’s62,27. Though the degree of reliance on nodulation for nitrogen fixation varies throughout legumes, it is perpetually present. For instance, in soybean, nodulation can contribute to a significant proportion of the plant's nitrogen needs, with non-nodulating variants often displaying stunted growth and reduced yields85. Similarly, nodulation is critical for optimal growth in common beans, especially under nitrogen-deficient conditions18. Further investigations into the performance of NNG and NG under varying nitrogen availability can offer insights into their adaptability and yield potential across different soil conditions.
The present investigation aimed to bridge a crucial gap in the existing knowledge base by assessing the impact of nodulation on agro-morphological and yield traits in chickpea. Our results align with existing literature on the positive effects of rhizobial nodulation on various growth characteristics, emphasizing the importance of this symbiotic association. The observed higher values in PH, PBr, biomass, and yield traits in NG compared to NNG underscore the pivotal role of rhizobial nodulation in enhancing plant growth and productivity in chickpea (Table 2) and mobilization of insoluble nutrients in the soil, leading to improved nutrient uptake in other legumes4,12. In addition, the absence of rhizobium nodulation resulted in a significant reduction in various growth parameters which might be due to a deficit in (a) host-dependent strain fitness11, (b) up-regulated expression of nif genes related to flavonoid synthesis83, and (c) maintenance of plant Pi (Inorganic phosphate) levels50.
The estimation of genetic variability and inheritance through GCV, PCV and heritability allows the breeders to identify the traits with substantial genetic control and potential for selection in crop improvement programs. For phenological traits, the small difference between GCV and PCV values suggests a predominant influence of genetic factors on their variance. HI exhibited low estimates of both PCV and GCV, indicating a more substantial influence of environment (Supplementary table 2 and 3). This aligns with previous studies highlighting the major role of genetic components in the inheritance of flowering, maturity, and the environmental factors in determining HI8,51,56,76. For the traits NPPP, NSPP, HI, PBr, and SBr, a magnitude of low to high heritability was observed, suggesting several genetic factors controlling the inheritance of these traits. In particular, SY demonstrated a high magnitude of GCV, PCV, and heritability emphasizing its potential for genetic improvement through simple selection even in early generations efficiently35,40,42,51,76. This diverse heritability pattern underscores the importance of trait-specific breeding strategies to achieve improvements in chickpea agronomics25,47,56,76. High heritability coupled with high GAM was recorded for SY and SW100 across seasons (Supplementary table 2 and 3), indicating the predominance of additive gene action for these traits. Similar findings were reported under diverse genetic backgrounds in chickpea42,54,60, blackgram13 as well as in cowpea53,26.
Interestingly, the association among SY, NPPP, and NSPP was significantly positive in both NG and NNG (Fig. 2). This indicates the possibility of simultaneous improvement of multiple traits in chickpea genotypes and cowpea advanced breeding lines8,26,53,59. The ability to enhance multiple traits concurrently is crucial for developing improved chickpea varieties with enhanced agronomic performance. Further analysis of the genotypes for their yield and stability using GT bi-plot identified the checks, Phule Vikram and RVG 204 on its vertex with high values for all the traits under the study which can be considered the best adaptable genotypes (Fig. 4). For SY, PH, and SW100, the NG #68, 159, 13, 17, 187, and 123 while 106, 109, and 46 for DFF and DM were best adaptable over the seasons. Comparable research of this kind in various crops7,55,75, provide a valuable insight for the selection of superior genotypes with enhanced adaptability and nodulating nature in the chickpea breeding programs.
The impact of rhizobium nodulation on grain yield and its association with yield-related traits was prominent in different legume crops. Earlier studies in chickpea emphasized the role of nodulation in enhancing seed yield and pod development8,42. Similarly, the seed yield was significantly improved by 40% in cowpea2, 33% in common bean18, and 45.6–50% in faba bean24,74 compared to control or non-inoculated treatments, indicating the critical role of symbiotic nitrogen fixation in achieving higher seed yields in legumes. Moreover, the crop-specific strains, soils, and weather factors are crucial in achieving yields. These shared trends highlight the conserved nature of the nodulation mechanism inherited historically for thriving legume crops under diverse agro-ecologies.
The comprehensive assessment of genetic variability, heritability, and genetic advance in this study provides a robust foundation for future chickpea breeding programs. The identification of traits with high heritability and substantial genetic advance, coupled with positive correlations among yield-related parameters, highlights avenues for effective genetic improvement. However, it's crucial to recognize the crop-specific nature of these findings and to tailor breeding strategies accordingly. Future research should delve deeper into the molecular mechanisms underpinning nodulation in chickpea and explore comparative studies across leguminous crops to enhance our understanding of these complex interactions.