Tulasnella can contribute to breakthrough in germination of the medicinal orchid Bletilla striata via producing plant hormones

Abstract

Bletilla striata (Thund.) Reichb. f. is a perennial herb in the Orchidaceae with both ornamental and medicinal value. Because its seed is so thin without endosperm, it is extremely difficult to germinate under natural conditions. For this study, we first observed the mycorrhizal construction of B. striata, the cortical cells were colonized by a large number of hyphae, with colonization rates ranging from 50% to 70%. Then, the nursery cups were used to bait symbiotic mycorrhizal fungi in native B. striata areas. Subsequently, four strains of Tulasnella were isolated and purified, of which one strain was from two-year-old B. striata (CFE 3) and three strains were from symbiotic germination B. striata (CFE 14, CFE 15, and CFE 25). The symbiotic germination experiment was developed. Germination in the presence of four mycorrhizal fungi showed separately 53% (CFE 3), 53% (CFE 14), 61% (CFE 15) and 67% (CFE 25) germination compared to 39% of control plants in 35 DAI. The results of the growth-promoting experiment demonstrated that CFE 25 could better promote the growth of leaves and roots. The range of seedlings, leaf lengths and main root lengths were significant improved 2.8, 2.4 and 13.6 times, respectively. CFE 15 was more beneficial for the growth of pseudobulbs and fresh weight, which were remarkably enhanced by 1.5 and 5.8 times. Finally, the germination and growth promotion efficiency was significantly related to the hormone content produced by Tulasnella. Our research revealed that the Tulasnella genera fungi from the mycorrhiza of B. striata can promote seed germination and seedling growth via producing plant hormones.