Sclerotinia minor Jagger is the causal agent of Sclerotinia blight, a highly destructive disease of peanut (Arachis hypogaea). Based on evidence that oxalic acid is involved in the pathogenicity of many Sclerotinia species, our objectives were to recover transgenic peanut plants expressing an oxalic acid-degrading oxalate oxidase and to evaluate them for increased resistance to S. minor. Transformed plants were regenerated from embryogenic cultures of three Virginia peanut cultivars (Wilson, Perry, and NC-7). A colorimetric enzyme assay was used to screen for oxalate oxidase activity in leaf tissue. Candidate plants with a range of expression levels were chosen for further analysis. Integration of the transgene was confirmed by Southern-blot analysis, and gene expression was demonstrated in transformants by northern-blot analysis. A sensitive fluorescent enzyme assay was used to quantify expression levels for comparison to the colorimetric protocol. A detached leaflet assay tested whether transgene expression could limit lesion size resulting from direct application of oxalic acid. Lesion size was significantly reduced in transgenic plants compared to nontransformed controls (65%-89% reduction at high oxalic acid concentrations). A second bioassay examined lesion size after inoculation of leaflets with S. minor mycelia. Lesion size was reduced by 75% to 97% in transformed plants, providing evidence that oxalate oxidase can confer enhanced resistance to Sclerotinia blight in peanut.Sclerotinia blight of peanut, caused by the necrotrophic fungus Sclerotinia minor, is one of the most devastating diseases of peanut (Arachis hypogaea) in Virginia, northeastern North Carolina, Oklahoma, and Texas. The fungicide fluazinam provides some protection (Smith et al., 1992), but its benefit to peanut producers is offset by the expense of the multiple applications necessary to achieve modest control. Yield losses due to Sclerotinia blight can be significant. For example, prior to the availability of fluazinam, losses to Sclerotinia blight averaged 10% in Virginia, with pod loss exceeding 50% in severely affected fields (Porter and Melouk, 1997).Oxalic acid is considered a pathogenicity factor in Sclerotinia sclerotiorum and many other fungal pathogens (Maxwell and Lumsden, 1970;Godoy et al., 1990 (Rao and Tewari, 1987), and S. minor (Hollowell et al., 2001). Direct application of oxalic acid to stem or leaf tissue causes marked tissue injury and wilting, similar to plant responses to fungal infection by S. rolfsii (Bateman and Beer, 1965) and S. sclerotiorum (Noyes and Hancock, 1981). The most compelling evidence for the involvement of oxalic acid in disease initiation was the demonstration that mutant isolates of S. sclerotiorum, deficient in oxalic acid production, were not pathogenic on bean (Phaseolus vulgaris), but revertants became pathogenic once they regained the ability to produce oxalic acid (Godoy et al., 1990). Screening for resistance to oxalic acid has also been studied as an indirect test of physiological resist...

Excised leaflets from mature embryos of peanut cultivars Robut, Gajah, McCubbin and NC-7 produced multiple shoot primordia via organogenesis on Murashige and Skoog medium supplemented with 3 mg L-1 BAP and 1 mg L-1 NAA. Plants were regenerated by elongation of shoot primordia on transfer to MS medium supplemented with 5 mg L-1 BAP. The regeneration frequency of five plants per embryonic leaflet was 10-40-fold higher than previously reported from seedling leaflets. Microprojectile bombardment parameters were optimised for high transient expression rates of the β-glucuronidase (uidA or gus) reporter gene in peanut embryos (> 2000 cells per bombardment) and in excised embryonic leaflets (> 1200 cells per bombardment). The firefly luciferase reporter gene (luc) allowed repeated non-toxic assays, revealing the transition from hundreds of transiently expressing cells soon after bombardment, to a few stably expressing regions in callus grown without selection for 8 weeks after bombardment of embryonic leaflets.

Transgenic peanut lines expressing oxalate oxidase, a novel enzyme to peanut, were evaluated for resistance to Sclerotinia blight in naturally infested fields over a 5-year period. Area under the disease progress curve (AUDPC) for transgenic lines in single rows planted with seed from single-plant selections averaged 78, 83, and 90% lower than nontransgenic parents in 2004, 2005, and 2006, respectively. In addition, AUDPC in 14 transgenic lines planted with bulked seed in two-row plots averaged 81% lower compared with nontransgenic parents in 2005 and 86% lower in 16 transgenic lines in 2006. Six transgenic lines yielded 488 to 1,260 kg/ha greater than nontransgenic parents in 2005, and 10 lines yielded 537 to 2,490 kg/ha greater in 2006. Fluazinam (0.58 kg a.i./ha) fungicide sprays in 2008 and 2009 reduced AUDPC in transgenic and nontransgenic lines but AUDPC was lowest in transgenic lines. Without fluazinam, yields of transgenic lines averaged 1,133 to 1,578 kg/ha greater than nontransgenic lines in 2008 and 1,670 to 2,755 kg/ha greater in 2009. These results demonstrated that the insertion of barley oxalate oxidase in peanut conveyed a high level of resistance to Sclerotinia blight, and negated the need for costly fungicide sprays.

Sediment cores spanning the last two centuries were taken in Hagelseewli, a high-elevation lake in the Swiss Alps. Contiguous 0.5 cm samples were analysed for biological remains, including diatoms, chironomids, cladocera, chrysophyte cysts, and fossil pigments. In addition, sedimentological and geochemical variables such as loss-onignition, total carbon, nitrogen, sulphur, grain-size and magnetic mineralogy were determined. The results of these analyses were compared to a long instrumental air temperature record that was adapted to the elevation of Hagelseewli by applying mean monthly lapse rates.During much of the time, the lake is in the shadow of a high cliff to the south, so that the lake is ice-covered during much of the year and thus decoupled from climatic forcing. Lake biology is therefore influenced more by the duration of ice-cover than by direct temperature effects during the short open-water season. Long periods of ice-cover result in anoxic water conditions and dissolution of authigenic calcites, leading to carbonate-free sediments.The diversity of chironomid and cladoceran assemblages is extremely low, whereas that of diatom and chrysophyte cyst assemblages is much higher. Weak correlations were observed between the diatom and chrysophyte cyst assemblages on the one hand and summer or autumn air temperatures on the other, but the proportion of variance explained is low, so that air temperature alone cannot account for the degree of variation observed in the palaeolimnological record.Analyses of mineral magnetic parameters, spheroidal carbonaceous particles and lead suggest that atmospheric pollution has had a significant effect on the sediments of Hagelseewli, but little effect on the water quality as reflected in the lake biota. This is the eighth of 11 papers published in this special issue on the palaeolimnology of remote mountain lakes in Europe resulting from the MOLAR project funded by the European Union. The guest editor was Richard W. Battarbee.

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