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Dawson, GA, United States

Koike S.T.,University of California Cooperative Extension | Arias R.S.,National Peanut Research Laboratory | Hogan C.S.,U.S. Department of Agriculture | Martin F.N.,U.S. Department of Agriculture | Gordon T.R.,University of California at Davis
International Journal of Fruit Science

Macrophomina crown and root rot has become a significant soil-borne disease issue in California. For many locations in the state, the disease is associated with fields that are no longer pre-plant, flat field fumigated with methyl bromide + chloropicrin. Inoculation experiments indicated that some differences in strawberry cultivar susceptibility to Macrophomina phaseolina were seen a short time after the inoculation, but as disease progressed such differences did not persist. Preliminary characterization studies of Macrophomina phaseolina isolates from strawberry indicated that such isolates may have a host preference for strawberry. Macrophomina phaseolina isolates from watermelon, thyme, and apple failed to cause disease in strawberry. Five cover crop species, which can be rotated with strawberry, did not develop disease when inoculated with strawberry isolates. In preliminary analysis using simple sequence repeat markers, isolates obtained from strawberry formed a separate group compared to isolates recovered from other known Macrophomina phaseolina hosts. © 2016 Taylor & Francis Source

Devi J.M.,North Carolina State University | Rowland D.L.,University of Florida | Payton P.,U.S. Department of Agriculture | Faircloth W.,National Peanut Research Laboratory | Sinclair T.R.,North Carolina State University
Field Crops Research

Peanut is often grown in the U.S. on sandy soil with limited water holding capacity. Since nitrogen fixation activity of other grain legume species, and some peanut cultivars, has been found to be especially sensitive to soil drying, yield improvement may be possible by identifying and/or breeding cultivars with nitrogen fixation resistance to water-deficit conditions. A key in this approach will be the use of screens to identify genotypes that may express drought resistance. Two screens of differing experimental sophistication were explored in this study as potential tools to compare genotypes. The first screen was done in the greenhouse using intact plants in a flow-though acetylene reduction system to measure nitrogen fixation response to soil drying over about two weeks. Ten commercial cultivars were tested and the only significant difference in nitrogen fixation activity was between Georgia 06G and York. The threshold for the decline in the nitrogen fixation rate averaged at a relative high value of 0.37 but Georgia 06G had a relatively low value of 0.28. These thresholds are greater than have been reported for nitrogen fixation tolerance in other species. The second, less sensitive screen that can be applied to a much larger number of genotypes was done in the field by measuring nitrogen accumulation over 2-3 wks of growth on limited available soil water. There were no differences in nitrogen-to-mass accumulation ratio among the commercial cultivars during two limited-water experiments. However, data collected from the field on several breeding lines from India indicated a consistency in the identification of nitrogen fixation in the greenhouse experiment and field experiments. © 2013 Elsevier B.V. Source

Dang P.M.,National Peanut Research Laboratory | Chen C.Y.,Auburn University | Holbrook C.C.,U.S. Department of Agriculture
Functional Plant Biology

Drought can significantly limit yield and quality in peanut (Arachis hypogaea L.), depending on its timing, duration and severity. The objective of this study was to identify potential molecular mechanism(s) utilising a candidate-gene approach in five peanut genotypes with contrasting drought responses. An early season drought stress treatment was applied under environmentally controlled rain-out shelters. When water was completely withheld for 3 weeks, no physical differences were observed for treated plants compared with their fully irrigated counterparts as indicated by relative water content; however, yield, grades (total sound mature kernel, TSMK), specific leaf area, and leaf dry matter content showed significant differences. Comparing expression levels of candidate genes, 'C76-16' exhibited significantly higher levels for CuZnSOD, NsLTP and drought protein 1 week earlier compared to the other genotypes, followed by significantly lower levels for the same genes. This suggested an early recognition of drought in C76-16 followed by an acclimation response. Cultivar 'Georgia Green' showed different patterns of gene-expression than C76-16. AP-3, a susceptible genotype, showed generally lower levels of gene-expression than C76-16 and Georgia Green. Myo-inositol phosphate synthase gene-expression showed high levels in irrigated treatment, ranging from 4-fold for 08T-12 to 12-fold for Georgia Green, but were significantly inhibited in drought treatment after 2 weeks of drought and after recovery. © 2013 CSIRO. Source

Sundaram J.,National Peanut Research Laboratory | Kandala C.V.K.,National Peanut Research Laboratory | Butts C.L.,National Peanut Research Laboratory
Sensing and Instrumentation for Food Quality and Safety

One of the grading factors for peanuts is their classification into peanuts with good or bad kernels. Traditional manual methods are labor intensive and subjective. A device by which the classification could be done rapidly and without the need to shell the peanuts would be very useful for the peanut industry. In this work VIS/NIR spectroscopy was used for this purpose. Reflectance spectra were collected for peanut pods (in-shell peanuts) in the wavelength range of 400-2500 nm. A calibration group of about 200 pods were initially scanned to train the classification algorithm. Each individual pod was shelled and the kernels were visually examined and classified as bad if they had any kind of damage, discoloration or immaturity. The remaining pods were marked as good ones. The Principal component analysis model generated from primary spectra with or without pretreatments gave explained variance better than 99%. The maximum normalization model with the ability of characterizing good and bad kernels with an accuracy of 80% and with low SEP and RMSEP values of 0. 43, would be useful in the quality characterization of in-shell peanuts. © 2010 US Government. Source

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