Identification of a resistance gene Rpi-dlc1 to Phytophthora infestans in European accessions of Solanum dulcamara

Initial screening of 14 Solanum dulcamara accessions enabled the identification of individuals resistant and susceptible to Phytophthora infestans. Crosses between contrasting genotypes resulted in three F2–BC1 populations segregating for resistance to late blight in a laboratory assay and under field conditions. Genetic profiling of one of these populations using 128 AFLP primers generated three markers linked to the resistant phenotype. Blast analysis of the sequenced markers resulted in a plausible gene position on the distal end of the long arm of chromosome 9 that could be confirmed by CAPS markers. Thus, we describe a first resistant gene, named Rpi-dlc1, from S. dulcamara, a Solanum species native to Europe. In addition, one population was tested for broadness of resistance responses using a set of seven additional P. infestans isolates, varying in virulence. This indicated the possible presence of additional Rpi genes

Petunia Floral Defensins with Unique Prodomains as Novel Candidates for Development of Fusarium Wilt Resistance in Transgenic Banana Plants

Antimicrobial peptides are a potent group of defense active molecules that have been utilized in developing resistance against a multitude of plant pathogens. Floral defensins constitute a group of cysteine-rich peptides showing potent growth inhibition of pathogenic filamentous fungi especially Fusarium oxysporum in vitro. Full length genes coding for two Petunia floral defensins, PhDef1 and PhDef2 having unique C- terminal 31 and 27 amino acid long predicted prodomains, were overexpressed in transgenic banana plants using embryogenic cells as explants for Agrobacterium–mediated genetic transformation. High level constitutive expression of these defensins in elite banana cv. Rasthali led to significant resistance against infection of Fusarium oxysporum f. sp. cubense as shown by in vitro and ex vivo bioassay studies. Transgenic banana lines expressing either of the two defensins were clearly less chlorotic and had significantly less infestation and discoloration in the vital corm region of the plant as compared to untransformed controls. Transgenic banana plants expressing high level of full-length PhDef1 and PhDef2 were phenotypically normal and no stunting was observed. In conclusion, our results suggest that high-level constitutive expression of floral defensins having distinctive prodomains is an efficient strategy for development of fungal resistance in economically important fruit crops like banana

A review of plant options for mitigating nitrous oxide emissions from pasture-based systems

In grazed pasture-based systems, urinary-nitrogen (N) voided in concentrated patches is a key source of nitrous oxide (N₂O), a potent greenhouse gas (GHG). Development of strategies for reducing emissions from urine patches is an ongoing focus of international research. Plants can help mitigate N₂O emissions by reducing urinary-N excretion or by lowering the N₂O emission factor of urine. This paper reviews the current understanding of plant-effects on urinary-N₂O emissions and confirms that plants can influence emissions. Recent New Zealand studies suggest that plantain and fodder beet show particular potential for grazed systems. A key mechanism by which plantain affects the N₂O emission factor could be root exudates that inhibit nitrification and/or increase N immobilisation. Further studies are needed to elucidate the mechanisms involved, and to help maximise the GHG reduction potential from plant management options in pasture-based systems

Compaction influences N₂O and N₂ emissions from ¹⁵N-labeled synthetic urine in wet soils during successive saturation/drainage cycles

Nitrous oxide emitted from urine patches is a key source of agricultural greenhouse gas emissions. A better understanding of the complex soil environmental and biochemical regulation of urine-N transformations in wet soils is needed to predict N₂O emissions from grazing and also to develop targeted mitigation technologies. Soil aeration, gas diffusion and drainage are key factors regulating N transformations and are affected by compaction during grazing. To understand how soil compaction from animal treading influences N transformations of urine in wet soils, we applied pressures of 0, 220 and 400 kPa to repacked soil cores, followed by ¹⁵N-labeled synthetic urine, and then subjected the cores to three successive saturation–drainage cycles on tension tables from 0 to 10 kPa. Compaction had a relatively small effect on soil bulk density (increasing from 0.81 to 0.88 Mg m⁻³), but strongly affected the pore size distribution. Compaction reduced both total soil porosity and macroporosity. It also affected the pore size distribution, principally by decreasing the proportion of 30–60 μm and 60–100 μm pores and increasing the proportion of micropores (<30 μm). Rates of urine-N transformations, emissions of N₂ and N₂O, and the N₂O to N₂ ratio were affected by the saturation/drainage cycles and degree of compaction. During the first saturation–drainage cycle, production of both N₂O and N₂ was low (<0.4 mg N m⁻² h⁻¹), probably because of anaerobic conditions inhibiting nitrification. In the second saturation/drainage cycle, the predominant product was N₂ at all compaction rates. By the third cycle, with increasing availability of mineral-N substrates, N₂O was the dominant product in the uncompacted (max = 4.70 mg N m⁻² h⁻¹) and 220 kPa compacted soils (max = 7.65 mg N m⁻² h⁻¹) with lower amounts of N₂ produced, while N₂ was produced in similar quantities to N₂O (max = 3.11 mg N m⁻² h⁻¹) in the 400 kPa compacted soil. Reduced macroporosity in the most compacted soil contributed to more sustained N₂ and N₂O production as the soils drained. In addition, compaction affected the rate of change of soil pH and DOC, both of which affected the N₂O to N₂ ratio. Denitrification during drainage and re-saturation may make a large contribution to soil N₂O emissions. Improving soil drainage and adopting grazing management practices that avoid soil compaction while increasing macroporosity will reduce total N₂O and N₂ emissions