Medicago sativa is an important forage crop; its value is mainly concentrated in its economic aspects. The growth cycle and growth rate of M. sativa have an important influence on its economic benefits. Alternaria alstroemeriae has often been used as a pathogenic bacterium in previous studies, and studies on the growth-promoting effects of A. alstroemeriae are rare. This study aimed to assess the effects of A. alstroemeriae on the growth parameters of M. sativae and to investigate the molecular and metabolic mechanisms of M. sativa. M. sativa showed significant improvement in plant height, root length, fresh weight, and dry weight compared to uninoculated control plants. By integrating the results of transcriptome and metabolome analysis, A. alstroemeriae may promote plant growth by regulating genes associated with the biosynthetic pathways of flavonoids, anthocyanins, and proanthocyanidins in plants. These research findings provide a theoretical basis for future verification of the molecular response mechanisms and metabolic regulation of A. alstroemeriae-promoted plant growth. This study also provides a theoretical basis for sustainable agricultural development.

Most previous studies have focused on the pathogenicity of Fusarium species towards crops. In this study, a Fusarium isolate was obtained from healthy Chamelaucium uncinatum plants; its ITS rDNA sequence showed 99% similarity to that of Fusarium napiforme. The fermentation preparation derived from this isolate promoted the growth and biomass accumulation of Lolium perenne L., a high-quality temperate forage grass; following seed treatment with the fermentation broth, the germination rate increased from 61.5% to 82%. In the pot experiment, in which the fermentation preparation was applied by root irrigation, plant height and root length of the host plants increased significantly by 20.0% and 30.6% (p < 0.05) and dry weight increased by 67.6% (p = 0.010), whereas fresh weight showed a non-significant increasing trend (+22.5%, p = 0.136); no disease symptoms were observed. Integrated transcriptomic and metabolomic analyses showed that exposure to the fermentation broth was associated with changes in genes and metabolites related to biomass accumulation. This study identified a candidate fungal isolate for the future development of microbial inoculants for forage crops.