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Cropping soils vary in extent of natural suppression of soil-borne plant diseases. However, it is unknown whether similar variation occurs across pastoral agricultural systems. We examined soil microbial community properties known to be associated with disease suppression across 50 pastoral fields varying in management intensity. The composition and abundance of the disease-suppressive community were assessed from both taxonomic and functional perspectives. Pseudomonas bacteria were selected as a general taxonomic indicator of disease suppressive potential, while genes associated with the biosynthesis of a suite of secondary metabolites provided functional markers (GeoChip 5.0 microarray analysis). The composition of both the Pseudomonas communities and disease suppressive functional genes were responsive to land use. Underlying soil properties explained 37% of the variation in Pseudomonas community structure and up to 61% of the variation in the abundance of disease suppressive functional genes. Notably, measures of soil organic matter quality, C:P ratio, and aromaticity of the dissolved organic matter content (carbon recalcitrance), influenced both the taxonomic and functional disease suppressive potential of the pasture soils. Our results suggest that key components of the soil microbial community may be managed on-farm to enhance disease suppression and plant productivity.

Context: Biological nitrogen (N) fixation through the rhizobia–legume symbiosis is a sustainable and cost-effective source of N for agriculture. In New Zealand (NZ), white clover (Trifolium repens) is a key component of pastures and rhizobial inoculation of clover is widely used. The current commercial inoculant for white clover, TA1, was isolated in Australia in the 1950s and may not be the best partner for modern white clover cultivars. Aims: To identify Rhizobium leguminosarum bv. trifolii (Rlt) isolates suitable for use in NZ pastures. Methods: The symbiotic potential of >230 isolates collected from throughout NZ was evaluated in plant bioassays. Selected isolates were further evaluated in pot and field trials. Key results: Approximately 40% of NZ isolates supported better clover growth than TA1 under N-limited conditions in vitro. Of 24 Rlt isolates evaluated in a glasshouse trial, five produced significantly higher clover biomass than TA1. Three (S11N9, S20N7, S4N6) of nine isolates evaluated in two field trials in 2018–2019 significantly increased clover growth (12–38%) compared with paired uninoculated clover at several harvests, whereas inoculation with TA1 did not improve yield. In a third trial in 2020, S11N9 and S20N7 increased clover growth compared with the uninoculated control at two of three harvests; S4N6 performed better than TA1 at one harvest. When tested with four white clover cultivars, five Rlt isolates had higher symbiotic potential than TA1. Conclusions: Inoculating white clover would be beneficial if improved inoculant isolates were available. Implications: We recommend some NZ Rlt isolates could be developed into commercial inoculants to improve white clover performance in NZ. Enhancing biological nitrogen fixation through the rhizobia–legume symbiosis is urgent, as concerns over environmental impacts of intensive agriculture increase. Despite the importance of legumes in New Zealand's pastures, there has been little emphasis placed on rhizobium, and modern white clover cultivars still rely on a commercial inoculant TA1 isolated from 1950s. A few rhizobial isolates identified in this study performed better than TA1 and could be developed into commercial inoculants to improve white clover performance in New Zealand. [ABSTRACT FROM AUTHOR]

The Melolonthinae branch of the beetle family Scarabaeidae has evolved in isolation in Aotearoa, radiating into >100 endemic species, since Aotearoa separated from Gondwanaland 82 million years ago. The group includes important pasture pests, such as the New Zealand grass grub Costelytra giveni and the manuka beetle Pyronota festiva. These beetles, like other organisms, host their own distinctive microflora including beneficial microbial symbionts and pathogens. A wide range of microbial pathogens infect the Scarabaeidae, but in Aotearoa the bacteria Serratia entomophila, S. proteamaculans and S. quinivorans (Enterobacteriaceae) are frequently found causing natural disease epizootics in C. giveni. S. entomophila is widespread in Aotearoa pasture soils, with only rare isolations of S. entomophila documented in other countries. In contrast S. proteamaculans and S. quinivorans are globally ubiquitous, and are widely distributed within Aotearoa, with some isolates active against either C. giveni or Pyronota spp. larvae, or both. Virulence determinants that impart differential host specificity and potency are located on variants of the amber disease associated plasmid (pADAP). The host specificity of the Serratia-scarab system and the absence of similar systems in other geographies, suggests that the relationship between Serratia spp. and endemic scarabs has evolved in Aotearoa. [ABSTRACT FROM AUTHOR]

Ripgut brome (Bromus diandrus) is a significant weed in arable systems with cereals being negatively impacted through yield reduction and contamination of harvested grain. There are limited herbicide options for its control, and reduction of the weed seed bank is a key part of its management. Ripgut brome seeds were incubated in three soils known to harbour a range of plant pathogens, and a range of fungi were subsequently isolated from ungerminated seeds. The most prevalent putative fungal pathogens isolated were Fusarium spp. and Marasmius sp. Selected isolates were cultured on artificial media and tested for their ability to inhibit germination of ripgut brome seeds in a series of in vitro assays, with many isolates completely inhibiting germination. When isolates were tested for their activity against non-target arable species in plant assays, three of five Fusarium spp. isolates significantly inhibited germination of oats and barley while a Marasmius sp. isolate had no effect on germination of these species. Further plant assays using four Marasmius sp. isolates against a wider range of plant species (oats, barley, ryegrass, brome, cocksfoot, and prairie grass) indicated some variability between Marasmius sp. isolates, with two isolates slightly inhibiting germination of some plant species, while two isolates (W14, W17) had no adverse effects. Sequencing of the ITS region of the Marasmius sp. isolates indicated that they were closely related but distinct from M. graminum, which is known to have some phytopathogenic activity and M. oreades which has not yet been reported as a plant pathogen. Further investigation of the Marasmius isolates as potential biocontrol agents for ripgut brome seed is warranted. [ABSTRACT FROM AUTHOR]

A customised synthetic microbial community (SynCom) composed of carefully selected rhizosphere-competent bacterial strains improved rice growth, yield and resistance to soil acidity and Al toxicity. [ABSTRACT FROM AUTHOR]

Evidence for the putative mobility of the sep genes of Serratia spp. plasmid pADAP is described. Analysis showed that orthologues of the sep genes reside on plasmids within S. entomophila, S. liquefaciens, S. proteancuals, and a plasmid form Yersinia frederiksenii indicating that these genes are part of a discrete horizontally mobile region.

Multispecies grasslands can alter nitrogen (N) cycling processes. A mesocosm experiment was performed comparing bare soil, soil planted with perennial ryegrass (Lolium perenne), white clover (Trifolium repens), plantain (Plantago lanceolata), and a mixed sward with all three species. We aimed to assess the plant effects on: ruminant urine-induced dry matter yields, plant N uptake, soil N2O emissions, and genes encoding nitrifier and denitrifier N transformations. After 35 days urine application increased both dry matter in the plantain (11%) and mixed (19%) swards, and N uptake in the ryegrass (63%), plantain (120%) and mixed (103%) swards. Urine increased cumulative N2O emissions, and while there was a trend for greater N uptake to cause lower emissions this was not significant. Urine addition elevated inorganic-N concentrations with few differences between plant treatments. Ammonia oxidising bacteria increased under urine but plantain did not inhibit this response. On days 3–10, increases in nirK and nosZI were indicative of enhanced nitrifier-denitrification and N2O scavenging by denitrifiers, respectively. The elevation of nosZI under urine-affected soil warrants further investigation in relation to potential pasture species effects. Consistent with previous in situ studies this study showed no evidence of plantain affecting soil inorganic-N concentrations via biological nitrification inhibition. [ABSTRACT FROM AUTHOR]