Cytokinin Production by the Rice Blast Fungus Is a Pivotal Requirement for Full Virulence.

Plants produce cytokinin (CK) hormones for controlling key developmental processes like source/sink distribution, cell division or programmed cell-death. Some plant pathogens have been shown to produce CKs but the function of this mimicry production by non-tumor inducing pathogens, has yet to be established. Here we identify a gene required for CK biosynthesis, CKS1, in the rice blast fungus Magnaporthe oryzae. The fungal-secreted CKs are likely perceived by the plant during infection since the transcriptional regulation of rice CK-responsive genes is altered in plants infected by the mutants in which CKS1 gene was deleted. Although cks1 mutants showed normal in vitro growth and development, they were severely affected for in planta growth and virulence. Moreover, we showed that the cks1 mutant triggered enhanced induction of plant defenses as manifested by an elevated oxidative burst and expression of defense-related markers. In addition, the contents of sugars and key amino acids for fungal growth were altered in and around the infection site by the cks1 mutant in a different manner than by the control strain. These results suggest that fungal-derived CKs are key effectors required for dampening host defenses and affecting sugar and amino acid distribution in and around the infection site.

Potential of an alternative prey to disrupt predation of the generalist predator, Orius insidiosus, on the pest aphid, Aphis glycines, via short-term indirect interactions.

Generalist insect predators can significantly impact the dynamics of pest populations; and, using alternative prey, they can rapidly establish in disturbed agroecosystems. However, indirect interactions between prey can occur, leading to either increased or decreased predation on focal prey. The present paper demonstrates how alternative prey can disrupt predation by the hemipteran Orius insidiosus on the soybean aphid Aphis glycines via short-term indirect interactions. We used laboratory microcosms to measure the impact of the predator on the population growth of the aphid in the presence of alternative prey, soybean thrips Neohydatothrips variabilis, and we characterized the foraging behaviour of the predator to assess prey preference. We showed that O. insidiosus predation on aphids was reduced in the presence of thrips and that this positive impact on aphids increased as thrips density increased. Results from the behavioural experiment support the hypothesis of a prey preference toward thrips. When prey-pest ratio is aphid-biased, short-term apparent commensalism between prey occurs in favour of the most abundant prey (aphids) with no switching behaviour appearing in O. insidiosus. These results demonstrate that potential indirect interactions should be taken into account when considering O. insidiosus as a biocontrol agent against the soybean aphid.

Economic threshold for soybean aphid (Hemiptera: Aphididae).

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), reached damaging levels in 2003 and 2005 in soybean, Glycine max (L.) Merrill, in most northern U.S. states and Canadian provinces, and it has become one of the most important pests of soybean throughout the North Central region. A common experimental protocol was adopted by participants in six states who provided data from 19 yield-loss experiments conducted over a 3-yr period. Population doubling times for field populations of soybean aphid averaged 6.8 d +/- 0.8 d (mean +/- SEM). The average economic threshold (ET) over all control costs, market values, and yield was 273 +/- 38 (mean +/- 95% confidence interval [CI], range 111-567) aphids per plant. This ET provides a 7-d lead time before aphid populations are expected to exceed the economic injury level (EIL) of 674 +/- 95 (mean +/- 95% CI, range 275-1,399) aphids per plant. Peak aphid density in 18 of the 19 location-years occurred during soybean growth stages R3 (beginning pod formation) to R5 (full size pod) with a single data set having aphid populations peaking at R6 (full size green seed). The ET developed here is strongly supported through soybean growth stage R5. Setting an ET at lower aphid densities increases the risk to producers by treating an aphid population that is growing too slowly to exceed the EIL in 7 d, eliminates generalist predators, and exposes a larger portion of the soybean aphid population to selection by insecticides, which could lead to development of insecticide resistance.

Survey of breakfast and infant cereals for aflatoxins B1, B2, G1 and G2.

Three hundred and forty-nine breakfast and infant cereal samples were collected at retail level across Canada from 2002 to 2005. They included rice-, soy-, barley-based and mixed-grain infant cereals, corn-, wheat-, rice-based and mixed-grain breakfast cereals, and were analysed for aflatoxins B1, B2, G1 and G2 using a modified AOAC International official method. An immunoaffinity column was used for the cleanup and purification of extracts. Determination of aflatoxins was by LC using post-column derivatization with pyridinium hydrobromide perbromide and fluorescence detection. Results indicated that 50% of both breakfast and infant cereals had detectable levels (limit of detection = 0.002 ng g-1) of aflatoxin B1, which is the most toxic of the four toxins. The levels found varied from 0.002 to 1.00 ng g-1 for aflatoxin B1, from 0.002 to 0.14 ng g-1 for aflatoxin B2, from 0.008 to 0.27 ng g-1 for aflatoxin G1, and from 0.008 to 0.048 ng g-1 for aflatoxin G2. Only 4% of the breakfast cereals and 1% of the infant cereals had aflatoxin B1 levels exceeding 0.1 ng g-1, which is the European Union maximum limit for aflatoxin B1 in baby foods and processed cereal-based foods for infants and young children.

Determination of ochratoxin A in green coffee by immunoaffinity column cleanup and liquid chomatography: collaborative study.

A collaborative study was conducted to evaluate a method using immunoaffinity column cleanup with liquid chromatography (LC) for the determination of ochratoxin A (OTA) in green coffee at levels that could be included in possible future regulations of the European Union. The test portion was extracted with methanol-3% aqueous sodium hydrogen carbonate solution (50 + 50, v/v). The extract was filtered, and the filtrate was diluted with phosphate-buffered saline and applied to an immunoaffinity column containing antibodies specific for OTA. After washing, the toxin was eluted from the column with methanol and quantified by LC with fluorescence detection. Pairs of 4 homogeneous noncontaminated and naturally contaminated materials (mean levels of < 0.12, 2.44, 5.15, and 13.46 ng/g) and blank samples (< 0.12 ng/g) for spiking were sent to 20 participant laboratories from 8 countries. The materials were analyzed according to the method description and all difficulties encountered in the analysis were reported. Statistical analysis was carried out according to the Harmonized Protocol of the International Union of Pure and Applied Chemistry. The relative standard deviation for repeatability (RSDr) ranged from 7.42 to 20.94%, and the relative standard deviation for reproducibility (RSDR) ranged from 16.34 to 29.17%. The method showed acceptable within-laboratory and between-laboratories precision for green coffee materials, as evidenced by HorRat values of < or = 0.85, at the studied range, for spiked and naturally contaminated materials. The mean recovery was 92.8% for green coffee material spiked with OTA at a level of 4.82 ng/g.

Ochratoxin A in wine and grape juice sold in Canada.

Ochratoxin A (OTA) was determined in 251 samples of wines and grape juice collected over 3 years in Canada. In total, 25/84 samples of red wine, 22/96 samples of white wine, 3/46 red grape juices and 1/25 white grape juices contained OTA levels above the limit of quantitation (LOQ). Canadian wines, when compared with imported products, showed both a lower OTA occurrence, noted as positive (19 versus 48% above the limit of detection (LOD) for wines), and a lower level of OTA contamination (upper bound mean of 17.5 versus 163pg ml(-1) for wines). Wines from the USA contained no quantifiable levels of ochratoxin A. OTA was found in Canadian and US grape juice samples, with 12.9% above the LOD and an upper bound mean of 13.3pg ml(-1). It was extracted from a wine or grape juice sample by passing it through an immunoaffinity column. The sample matrix was washed off the column with water. OTA was eluted from the column with methanol and quantitatively determined by liquid chromatography using a fluorescence detector. The presence of OTA was confirmed by esterification with boron trifluoride-methanol. The LOQ of OTA was estimated as 20 pg ml(-1) in white wine (S/N 10:1) and 40 pg ml(-1) in red wine, white grape juice and red grape juice (S/N 20.1). The LOD was estimated as 4pgml(-1) for white wine and 8pgml(-1) for red wine and white and red grape juices (S/N 3:1).