With the post-genomic era came a dramatic increase in high-throughput technologies, of which transcriptional profiling by microarrays was one of the most popular. One application of this technology is to identify genes that are differentially expressed in response to different environmental conditions. These experiments are constructed under the assumption that the differentially expressed genes are functionally important in the environment where they are induced. However, whether differential expression is predictive of functional importance has yet to be tested. Here we have addressed this expectation by employing Caenorhabditis elegans as a model for the interaction of native soil nematode taxa and soil bacteria. Using transcriptional profiling, we identified candidate genes regulated in response to different bacteria isolated in association with grassland nematodes or from grassland soils. Many of the regulated candidate genes are predicted to affect metabolism and innate immunity suggesting similar genes could influence nematode community dynamics in natural systems. Using mutations that inactivate 21 of the identified genes, we showed that most contribute to lifespan and/or fitness in a given bacterial environment. Although these bacteria may not be natural food sources for C. elegans, we show that changes in food source, as can occur in environmental disturbance, can have a large effect on gene expression, with important consequences for fitness. Moreover, we used regression analysis to demonstrate that for many genes the degree of differential gene expression between two bacterial environments predicted the magnitude of the effect of the loss of gene function on life history traits in those environments.

Cereal Chem. 83(3):259-268Starch was isolated from flour of four wheats representing hard red winter (Karl), hard red spring (Gunner), durum (Belfield 3), and spelt (WK 86035-8) wheat classes. Digital image analysis (IA) coupled with light microscopy was used to determine starch size distributions where the volume of granules was calculated as spherical particles or oblate spheroids. Starch granules were classified into three size ranges: A-type granules (>15 μm), B-type granules (5-15 μm), and C-type granules (<5 μm). An error was noted in using digital image analysis because the perimeter of some granules touch the edge (PTE) of the field being analyzed. To correct for this error, the PTE granules were manually replaced into the field by measuring their diameters and entering them into the database. The results showed differences in the starch size distributions between the classes of wheat evaluated, as well as the method of analysis. Four laser diffraction sizing (LDS) instruments were used to measure granule distributions of the four classes of wheat. LDS compared with IA resulted in a ≈40% underestimation of the A-type granule diameter and a ≈50% underestimation of the B-type granule diameter. A correction factor (adjustment) was developed from IA data to correct LDS analysis. LDS data correlations before adjustments to IA data were R 2 = 0.02 ns to 0.55 *** . After adjustment, these correlations improved to R 2 = 0.

The effect of five mycorrhizal fungi on the growth of 10 wheat cultivars under three phosphorus regimes was assessed in a greenhouse study. Six of the cultivars responded positively, while four responded negatively or were nonresponsive to mycorrhizal inoculation. The responses of the individual cultivars were consistent regardless of inoculum source, suggesting that mycorrhizal responsiveness is an inherited trait rather than a response to individual fungi. Mycorrhizal responsiveness decreased with P fertilization for cultivars that were dependent on the symbiosis, but it was unaffected by P fertilization in cultivars that were negatively impacted by the mycorrhizae. Mycorrhizal and P responsiveness of each cultivar were highly correlated (r = 0.94), suggesting that P responsiveness may be a good predictor of the mycorrhizal dependence of selected wheat cultivars. The relationship between wheat biomass production and percentage root colonization was positive for cultivars, which responded favorably to the symbiosis, and negative for cultivars, which responded negatively or were nonresponsive to mycorrhizal inoculation. Amendment with P did not significantly affect these relationships. To determine whether differences in mycorrhizal responsiveness are related to nutrient uptake by the fungus, 32P uptake of Turkey (responsive cultivar) and Newton (nonresponsive cultivar) was controlled by severing the mycorrhizal hyphae in a split-pot experiment. Plants with intact hyphae absorbed more 32P than those with severed hyphae for both cultivars, and significantly more counts per minute of 32P were evident in Newton than in Turkey, suggesting that mycorrhizal function is not impaired even in cultivars that do not display a biomass increase in response to mycorrhizal symbiosis. Keywords: vesicular–arbuscular mycorrhizae, pathogenesis, growth response, mycorrhizal symbiosis.

The responses of five C4, warm-season and five C3, cool-season tallgrass prairie grasses to phosphorus (P) fertilization, mycorrhizae, and soil microorganisms were compared in greenhouse studies. The warm-season grasses responded positively to mycorrhizae or to P fertilization, but mycorrhizal plants did not respond to P. The soil microflora reduced mycorrhizal plant dry weight and root colonization. In contrast, cool-season grasses did not respond to mycorrhizae or P fertilization. Soil microorganisms did not suppress cool-season plant growth, but root colonization was reduced in nonsterile soil. For the warm-season grasses there was an inverse relationship between mycorrhizal root colonization and P fertilization and a positive relationship between root colonization and plant dry weight. For the cool-season grasses there was also an inverse relationship between root colonization and P fertilization, but the relationship between root colonization and plant dry weight was negative. In both the warm-season and cool-season grasses, low levels of mycorrhizal root colonization persisted even when P fertilization was sufficient to eliminate mycorrhizal effects on plant growth. Thus, warm- and cool-season grasses display profoundly different strategies for nutrient acquisition. Key words: cool-season grasses, warm-season grasses, vesicular–arbuscular mycorrhizae.

The soybean cyst nematode (SCN), Heterodera glycines, is the major disease-causing agent limiting soybean production in the USA. The current management strategy to reduce yield loss by SCN involves the deployment of resistant soybean cultivars and rotation to non-host crops. Although this management scheme has shown some success, continued yearly yield loss estimates demonstrate the limitations of these techniques. As a result, new control strategies are needed to complement the existing methods. Reported here is a novel method of SCN control that utilises RNA interference (RNAi). Transgenic soybeans were generated following transformation with an RNAi expression vector containing inverted repeats of a cDNA clone of the major sperm protein (MSP) gene from H. glycines. The accumulation of MSP-specific short interfering RNA (siRNA) molecules were detected by northern blot analysis of transgenic soybeans. T0 plants displaying MSP siRNA accumulation were deployed in a bioassay to evaluate the effects of MSP interfering molecules on H. glycines reproduction. Bioassay data has shown up to a 68% reduction in eggs g–1 root tissue, demonstrating that MSPi transgenic plants significantly reduced the reproductive potential of H. glycines. An additional bioassay evaluating progeny nematodes for maintenance of reproductive suppression indicated that progeny were also impaired in their ability to successfully reproduce, as demonstrated by a 75% reduction in eggs g–1 root tissue. The results of this study demonstrate the efficacy of an RNAi-based strategy for control of the soybean cyst nematode. In addition, these results may have important implications for the control of other plant parasitic nematodes.

Nematodes are abundant consumers in grassland soils, but more sensitive and specific methods of enumeration are needed to improve our understanding of how different nematode species affect, and are affected by, ecosystem processes. High‐throughput amplicon sequencing is used to enumerate microbial and invertebrate communities at a high level of taxonomic resolution, but the method requires validation against traditional specimen‐based morphological identifications. To investigate the consistency between these approaches, we enumerated nematodes from a 25‐year field experiment using both morphological and molecular identification techniques in order to determine the long‐term effects of annual burning and nitrogen enrichment on soil nematode communities. Family‐level frequencies based on amplicon sequencing were not initially consistent with specimen‐based counts, but correction for differences in rRNA gene copy number using a genetic algorithm improved quantitative accuracy. Multivariate analysis of corrected sequence‐based abundances of nematode families was consistent with, but not identical to, analysis of specimen‐based counts. In both cases, herbivores, fungivores and predator/omnivores generally were more abundant in burned than nonburned plots, while bacterivores generally were more abundant in nonburned or nitrogen‐enriched plots. Discriminate analysis of sequence‐based abundances identified putative indicator species representing each trophic group. We conclude that high‐throughput amplicon sequencing can be a valuable method for characterizing nematode communities at high taxonomic resolution as long as rRNA gene copy number variation is accounted for and accurate sequence databases are available.

Wheat blast caused by Magnaporthe oryzae Triticum causes significant losses on wheat during outbreak years in several South American countries. Despite reports of wheat blast leaf lesions on some wheat cultivars, the importance of inoculum originating from leaves in severely affected commercial fields is disputed. It is generally considered that leaf lesions and/or sporulation on leaves do not usually appear before the occurrence of spike blast in wheat. The purpose of this study was to (i) determine the occurrence of wheat blast on basal leaves, (ii) estimate the number of conidia produced on these leaves, and (iii) determine the impact of current fungicide application practices on inoculum produced from sporulating lesions on basal wheat leaves. Inoculations at the three-leaf stage showed that certain cultivar and isolate combinations caused more disease on old wheat leaves than young expanding leaves. Under optimum conditions, M. oryzae had the potential to produce tens to hundreds of thousands of conidia on small amounts of wheat basal leaves. A mean of 1 669 000 conidia were produced on 1 g dry basal leaves of a highly susceptible cultivar under optimum conditions for sporulation. Conidia production on leaves coincided with spike emergence under both greenhouse and field conditions. When field studies were conducted under natural epidemic conditions, foliar fungicide applications reduced the amount of M. oryzae conidia on basal leaves by 62-77% compared to non-sprayed controls. An earlier application of foliar fungicides might reduce inoculum if conidia from basal leaves contribute to wheat spike blast development.

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