A survey of Miscanthus × giganteus and switchgrass plots throughout the midwestern and southeastern United States was conducted to determine the occurrence and distribution of plant-parasitic nematodes associated with these biofuel crops. During 2008, rhizosphere soil samples were collected from 24 Miscanthus × giganteus and 38 switchgrass plots in South Dakota, Iowa, and Illinois. Additional samples were collected from 11 Miscanthus × giganteus and 10 switchgrass plots in Illinois, Kentucky, Georgia, and Tennessee the following year. The 11 dominant genera recovered from the samples were Pratylenchus, Helicotylenchus, Xiphinema, Longidorus, Heterodera, Hoplolaimus, Tylenchorhynchus, Criconemella, Paratrichodorus, Hemicriconemoides, and Paratylenchus. Populations of Helicotylenchus, Xiphinema, and Pratylenchus were common and recorded in 90.5, 83.8, and 91.9% of the soil samples from Miscanthus × giganteus, respectively, and in 91.6, 75, and 83.3% of the soil samples from switchgrass, respectively. Prominence value (PV) (PV = population density × √frequency of occurrence/10) was calculated for the nematodes identified. Helicotylenchus had the highest PV (PV = 384) and was followed by Xiphinema (PV = 152) and Pratylenchus (PV = 72). Several of the nematode species associated with the two biofuels crops were plant parasites. Of these, Pratylenchus penetrans, P. scribneri, P. crenatus, Helicotylenchus pseudorobustus, Hoplolaimus galeatus, X. americanum, and X. rivesi are potentially the most damaging pests to Miscanthus × giganteus and switchgrass. Due to a lack of information, the damaging population thresholds of plant-parasitic nematodes to Miscanthus × giganteus and switchgrass are currently unknown. However, damage threshold value ranges have been reported for other monocotyledon hosts. If these damage threshold value ranges are any indication of the population densities required to impact Miscanthus × giganteus and switchgrass, then every state surveyed has potential for yield losses due to plant-parasitic nematodes. Specifically, Helicotylenchus, Xiphinema, Pratylenchus, Hoplolaimus, Tylenchorhynchus, Criconemella, and Longidorus spp. were all found to have population densities within or above the threshold value ranges reported for other monocotyledon hosts.
Rolling, potential erodible cropland predominates the Northeast dairy region so corn (Zea mays L.) acreage under no‐tillage (NT) or ridge tillage (RT) may increase. Farmer‐operated studies were conducted on well‐drained, moderately well‐drained, somewhat poorly drained, and poorly drained sites in 1986, 1987, and 1988 to evaluate the competitiveness of NT and RT corn systems relative to conventional or moldboard plow (MP) corn systems. Compared with MP, NT had lower plant populations in seven and lower grain yields in five of the 12 site‐year comparisons. Compared with MP, RT had lower plant populations in five and lower grain yields in two of the comparisons. In the 10 other comparisons, RT had higher (twice) or similar grain yields. Averaged across sites and years, MP compared with NT and RT had higher equipment costs ($26.25, $20.46, and $22.75/acre, respectively) and labor costs ($21.21, $16.26, and $18.33/acre, respectively). Higher herbicide and grain‐drying costs for NT in most site‐year comparisons offset lower equipment and labor costs, which resulted in higher variable production costs for NT compared with MP at two sites. Variable production costs of RT were the same or lower than MP. The break‐even price indicated that NT was economically competitive with MP at the well‐drained ($1.58 and $1.55/bu, respectively) and poorly drained sites ($2.08 and $2.16/bu, respectively). In contrast, RT was economically competitive at all sites. Although RT is economically competitive with MP in a 3‐yr corn rotation, RT is not easily adapted to the corn‐sod rotation in the Northeast.
The distribution of Pratylenchus spp. from bioenergy field plots in six states (Illinois, Iowa, South Dakota, Kentucky, Tennessee, Georgia) of the USA were surveyed. The species were identified based on morphology and morphometrics and further characterised based on fragment sequences of the 28S rRNA of the D2-D3 region. The region revealed variations in sequencing information that supports the morphological identification. In this work, six Pratylenchus spp. were detected: Pratylenchus brachyurus, P. crenatus, P. hexincisus, P. neglectus, P. penetrans and P. scribneri. Pratylenchus scribneri, P. crenatus, and P. penetrans were distributed most widely, with detection of 34, 29 and 15%, respectively. Pratylenchus hexincisus, P. brachyurus and P. neglectus were distributed sporadically, with detection rates of 10.0, 2.6 and 2.0%, respectively. A one-step multiplex PCR was developed for the simultaneous detection of P. scribneri, P. crenatus and P. penetrans. Sequence data from this research and NCBI were used to generate different primer sets that are species-specific. We have therefore designed three sets of primers that discriminate P. scribneri, P. crenatus and P. penetrans in multiplex PCR. All the tested primers have shown specificity and have no cross-reaction with the nontarget species. When used in a uniplex, duplex and triplex PCR, the selected three primers gave a unique electrophoretic DNA banding pattern characterised by a single DNA fragment for P. scribneri (ca 750), P. crenatus (ca 690), and P. penetrans (ca 520). The method could be used for routine diagnostic programmes.
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