The effects of the floral infection by a bacterial pathogen in a dioecious plant, Mallotus japonicus (Euphorbiaceae)

Abstract

Among all the different organs of a plant, flowers might have one of the most dynamic microbial communities, since many microbes are transmitted during flowering by insects and pollen. However, little is known about how these microbes affect floral characteristics and plant reproduction. Among the microbes transmitted to flowers, pathogens may have highly negative effects on plants' fitness. In this study, we investigated whether a bacterial pathogen, Erwinia mallotivora, occurs on flowers of the host plant Mallotus japonicus, and whether the transmission of the pathogen to flowers can result in systemic infection and/or reduction of fruit production. The pathogen has been reported to infect through leaves, while its ecology on flowers is unknown. We first confirmed the presence of the pathogen on flowers, indicating possible transmission by visitors or pollen. Then, we showed that the bacteria can infect the plant through flowers by inoculating the pathogen to both male and female flowers. Interestingly, the symptoms on leaves appeared earlier on the female plants than on the males. Besides, the inoculation significantly decreased fruit set of the female plants. Our results suggest a higher cost of infection in a female than in a male once the pathogen infected flowers. Although the effects of pathogen infection to flowers have rarely investigated in wild plants, it would be an interesting topic for future study if such sexual differences in the infection cost can cause sexual conflict and intraspecific adaptation load.

Are microbes growing on flowers evil? Effects of old flower microbes on fruit set in a wild ginger with one-day flowers, Alpinia japonica (Zingiberaceae)

“…Besides, we found significant negative associations between the proportion of the ASVs of Cluster 6 and fruit set based on the GLMM analysis, while we did not find such associations for seed set. Since Erwinia and Pseudomonas include plant pathogens that trigger abortion of flowers and fruits (Goumas et al 1999; Llontop et al 2020; Marre et al 2022; Young 1988), some of these bacteria might have negatively affected fruit development by infecting a reproductive organ. However, we cannot rule out other potential explanations about the correlation.…”

Population Ecology 2024 Editorial

“…This special feature reviewed context dependency of community assembly rules and synthesized the current understanding of how the relative importance of multiple assembly processes changes with spatial scales, complexity, and time, both in the long and short terms. Second, “Sex and biological communities,” organized by Masato Yamamichi, was published with three papers (Marre et al, 2023; Morita & Yamamichi, 2023; Yamamichi et al, 2023), supported by our Special Feature Editor, Dr Akihiko Mougi. This special feature investigated the various effects of sexual reproduction on structures of ecological communities.…”

Are microbes growing on flowers evil? Effects of old flower microbes on fruit set in a wild ginger with one-day flowers, Alpinia japonica (Zingiberaceae)

“…Besides, we found significant negative associations between the proportion of the ASVs of Cluster 6 and fruit set based on the GLMM analysis, while we did not find such associations for seed set. Since Erwinia and Pseudomonas include plant pathogens that trigger abortion of flowers and fruits (Young 1988;Goumas et al 1999;Llontop et al 2020;Marre et al 2022), some of these bacteria might have negatively affected fruit development by infecting a reproductive organ. Their effects may not be as drastic as reported for some flower-infecting pathogens (e.g., Marre et al 2022); it decreased expected fruit set from 0.57 in open control to 0.35.…”

“…Since Erwinia and Pseudomonas include plant pathogens that trigger abortion of flowers and fruits (Young 1988;Goumas et al 1999;Llontop et al 2020;Marre et al 2022), some of these bacteria might have negatively affected fruit development by infecting a reproductive organ. Their effects may not be as drastic as reported for some flower-infecting pathogens (e.g., Marre et al 2022); it decreased expected fruit set from 0.57 in open control to 0.35. Fruit set of the paper-bagged and water-sprayed flowers were in between, possibly because high humidity caused by the treatment had promoted the growth of Cluster 6 as discussed in the previous section and then affected fruit set.…”