Endophytic fungi are increasingly studied for their ability to enhance plant performance in field crops, yet there are few equivalent studies in floricultural crops. Given the economic importance of these crops and pressures faced by growers to produce plants of high aesthetic quality, we surveyed the natural occurrence of foliar fungal endophytes in Knock Out® roses to identify candidate beneficial isolates. We also tested the effects of entomopathogenic fungal inocula on marigold and zinnia plant growth using different application approaches. Our survey of Knock Out® rose foliage collected from five sites within central Texas revealed at least 24 different fungal genera and 30 probable species, including some isolates providing plant stress tolerance and pathogens or antagonists of insects and nematode pests. The effects of entomopathogen inocula on plant growth varied with host plant (marigold vs. zinnia) and inoculation method (soil drench vs. seed soak). Plant responses were complex, but inoculation with Isaria fumosorosea Wize tended to have a negative effect on plant performance characteristics whereas Beauveria bassiana (Bals.-Criv.) Vuill. tended to have positive effects. When applied to marigold as a seedcoating, I. fumosorosea reduced germination, seedling fresh weight, and produced seedlings with a less compact form. By contrast, seeds inoculated with B. bassiana required less time to germinate, had higher germination rates, and increased the plant compactness. These results show that the impact of fungal entomopathogens applied as endophytes depends on the specific fungi-plant combination being examined. The effect of plant inoculation with entomopathogenic fungi within a pest management context requires further evaluation.
This research was financially supported by the American Floral Endowment and gifts-in-kind from Ernst Benary of America, Inc. (EBA).
We are grateful to Doug Holden (EBA Global Head of Breeding) and Norbert Müller (EBA Global Head of Supply Chain) for sharing their expertise on the seed coating chemistry and for providing horticultural expertise. We also thank Cesar Valencia, lab manager for G.A. Sword, for his guidance in developing and performing the endophyte culturing techniques required for this study. A previous draft of this manuscript was improved greatly by comments provided by S.P. Arthurs and H.B. Pemberton.
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