Promoting Effects of Piriformospora indica on the Growth and Development of Asparagus (Asparagus officinalis L.) Seedlings

As an endophytic fungus, <i>Piriformospora indica</i> has attracted great attention for its plant growth- and stress resistance-promoting effects on various host plants. However, up until now, there have been no reports on its application in asparagus. In this study, we report the colonization ability of <i>P. indica</i> in the roots of three asparagus varieties, 'Guanjun' (GJ), 'Fengdao No. 2' (FD), and 'Jin Lusun No. 1' (JL), with colonization ratios of 80.0%, 76.6%, and 73.3%, respectively. The influences of this fungal colonization on the growth of GJ, FD, and JL seedlings were further studied by determining the growth- and phytohormone-related parameters. The results showed that, at 2 months post inoculation (mpi), the <i>P. indica</i>-colonized seedlings exhibited improved total root length, peroxidase (POD) activity, and jasmonic acid (JA) accumulation in their roots and photosynthetic pigment accumulation in the leaves of all three varieties. At 8 mpi, most of the detected growth-related parameters, such as plant height, stem number and width, dry weight, photosynthetic pigment accumulation, and POD activity, were improved by the fungal colonization. However, the contents of 1-aminocyclopropane-1-carboxylic acid (ACC) in the <i>P. indica</i>-colonized roots were lower than that in the non-colonized ones. Moreover, the fungus's promoting effects on GJ were found to be the best of the three varieties. These results indicate that <i>P. indica</i> colonization can promote asparagus seedling growth and development by enhancing root development and by regulating phytohormone balance, with some variety-specific and temporal differences.