Abstract
Digitaria ischaemum (Schreb.) Schreb. ex Muhl. and Poa annua L. are competitive, early successional species which are usually considered weeds in agricultural and turfgrass systems. Bacteria and fungi associated with D. ischaemum and P. annua seed may contribute to their competitiveness by antagonizing competitor forbs, and were studied in axenic culture. Pantoea spp. were the most common bacterial isolate of D. ischaemum seed, while Epicoccum and Curvularia spp. were common fungal isolates. A variety of species were collected from non-surface sterilized P. annua. Certain Pantoea spp. isolates were antagonistic to competitor forbs Taraxacum officinale, Trifolium repens. All bacterial isolates that affected T. officinale mortality were isolated from D. ischaemum seed while none of the P. annua isolates affected mortality. Two selected bacterial isolates identified as Pantoea ananatis were evaluated further on D. ischaemum, T. repens (a competitor forb) and P. annua (a competitor grass) alone and in combination with a Curvularia sp. fungus. These bacteria alone caused >65% T. repens seedling mortality but did not affect P. annua seedling mortality. These experiments demonstrate that Pantoea ananatis associated with D. ischaemum seeds is antagonistic to competitor forbs in axenic culture. The weedy character of D. ischaemum could at least in part stem from the possession of bacteria that are antagonistic to competitor species.
Highlights
Digitaria species are some of the most competitive C4 weeds of agricultural, horticultural and turfgrass landscapes in tropical and temperate regions
Two Pantoea isolates of interest (4 and 5) were identified as Pantoea ananatis based on both 16S sequence similarity to Pantoea spp. and tuf gene sequences with >99% similarity to Pantoea ananatis
Our experiments demonstrate that D. ischaemum seed contains cultivable bacteria of the Pantoea genus and at least two cultivable fungi in genera Epicoccum and Curvularia
Summary
Digitaria (crabgrass) species are some of the most competitive C4 weeds of agricultural, horticultural and turfgrass landscapes in tropical and temperate regions. Digitaria sanguinalis is known to produce allelochemicals that may contribute to its competitiveness, but these have not been studied extensively [2,3]. Poa annua is another prolific early successional C3 plant that is extremely competitive in turfgrass and horticultural systems and can be found on all seven continents [4]. A wide range of endophytes are commonly found in plants, there are several potential mechanisms that reduce microbial endophyte density and diversity when compared with the root rhizosphere [6,9] These endophytes can affect tolerance to abiotic and biotic stressors such as disease, drought, heat and salinity [10,11]
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