Dominant Fungal Epiphytes Promote Growth of the Invasive Plant Ipomoea cairica Through Hormone Interactions

Abstract

Plant growth-promoting microbial symbionts have been found in many plants, but their association with invasive plant Ipomoea cairica remains largely unknown. The present study aimed to screen such microbes from the fungal epiphyte community of I. cairica. A total of 858 culturable isolates grouped into 20 morphotypes associated with 10 genera were recovered from healthy leaves of I. cairica. According to morphological and molecular identification, morphotypes Ep2 with 51.74% and Ep19 with 39.86% relative abundance in the epiphyte community were determined as dominant and identified as Fusarium fujikuroi and Fusarium oxysporum. In vitro analysis revealed that both epiphytes were active in producing indole-3-acetic acid (IAA) but not gibberellin-3 (GA3). Compared to F. oxysporum, F. fujikuroi accumulated significantly higher IAA concentration in its culture. The belowground biomass of I. cairica cuttings was significantly increased by F. oxysporum culture extract. Besides belowground biomass, F. fujikuroi culture extract significantly increased the aboveground biomass, and the number and total length of secondary shoots. In vivo inoculation showed that the conidial suspension of F. oxysporum significantly increased endogenous IAA level, the aboveground and belowground biomass of I. cairica cuttings, while the conidial suspension of F. fujikuroi slightly elevated endogenous IAA level only resulting in a significantly improved aboveground biomass. Our results revealed both of the dominant epiphytes promoted the growth of I. cairica through hormone interactions.