C. C. Holbrook

University of Georgia, Атина, Georgia, United States

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Publications (65)62.91 Total impact

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    ABSTRACT: Field experiments were conducted at Tifton, Georgia from 2008 to 2014 to determine the effects of new peanut (Arachis hypogaea) cultivars and in-furrow applications of phorate insecticide on severity of tomato spotted wilt (TSW) caused by Tomato spotted wilt virus. Several cultivars, including Florida-07, Georgia-06G, Georgia-07W, Georgia Greener, and Tifguard, had final incidence of TSW that were less than that of Georgia Green. In-furrow applications of phorate insecticide reduced incidence of TSW in Georgia Green in three experiments in which that cultivar was included. In-furrow application of phorate insecticide reduced incidence of TSW in most cases where incidence in nontreated plots was 10% or higher. Cultivars Georganic, and Georgia-10T, had final incidence of TSW that was lower than that of Georgia-06G, or Florida-07 within nontreated plots across 2011–2012. Georgia-10T and Georgia-12Y had final incidence that was lower than that of Georgia-06G, Georgia-07W, Georgia-09B and Georgia Greener across insecticide treatments in 2013. In-furrow application of phorate increased yields across cultivars in 2008–2009, and increased yield of Georgia-09B in 2010. In most other cases, phorate had no significant effect on yield. With higher levels of field resistance in most of these cultivars, especially those such as Georgia-12Y, benefits from use of phorate insecticide for TSW suppression were small, and typically did not result in yield increase. Based on these results, several of these cultivars should allow greater flexibility for insecticide choice for thrips management without increasing the risk of losses to TSW.
    No preview · Article · Mar 2016
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    ABSTRACT: Peanut, a high-oil crop with about 50% oil content, is either crushed for oil or used as edible products. Fatty acid composition determines the oil quality which has high relevance to consumer health, flavor, and shelf life of commercial products. In addition to the major fatty acids, oleic acid (C18:1) and linoleic acid (C18:2) accounting for about 80% of peanut oil, the six other fatty acids namely palmitic acid (C16:0), stearic acid (C18:0), arachidic acid (C20:0), gadoleic acid (C20:1), behenic acid (C22:0), and lignoceric acid (C24:0) are accounted for the rest 20%. To determine the genetic basis and to improve further understanding on effect of FAD2 genes on these fatty acids, two recombinant inbred line (RIL) populations namely S-population (high oleic line 'SunOleic 97R' × low oleic line 'NC94022') and T-population (normal oleic line 'Tifrunner' × low oleic line 'GT-C20') were developed. Genetic maps with 206 and 378 marker loci for the S- and the T-population, respectively were used for quantitative trait locus (QTL) analysis. As a result, a total of 164 main-effect (M-QTLs) and 27 epistatic (E-QTLs) QTLs associated with the minor fatty acids were identified with 0.16% to 40.56% phenotypic variation explained (PVE). Thirty four major QTLs (>10% of PVE) mapped on five linkage groups and 28 clusters containing more than three QTLs were also identified. These results suggest that the major QTLs with large additive effects would play an important role in controlling composition of these minor fatty acids in addition to the oleic and linoleic acids in peanut oil. The interrelationship among these fatty acids should be considered while breeding for improved peanut genotypes with good oil quality and desired fatty acid composition.
    Full-text · Article · Apr 2015 · PLoS ONE
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    ABSTRACT: A reliable peanut root transformation system would be useful to study the functions of genes involved in root biology and disease resistance. The objective of this study was to establish an effective protocol to produce composite plants mediated by Agrobacterium rhizogenes transformation. In total, 75% of transformed peanut seedlings produced an average of 2.83 transgenic roots per plant. Peanut seed had the highest germination rate after treatment in a chlorine gas chamber for 8 h compared with 16 h in chlorine gas or Clorox and mercuric chloride immersion treatments. High transformation efficiency was achieved when the wound site for A. rhizogenes inoculation was covered with vermiculite instead of enclosing the whole plant in a high humidity chamber. On average, 2.5 galls from Meloidogyne arenaria infection were formed per transgenic root from susceptible genotype TifGP-2. These data indicate that A. rhizogenes-transformed roots can be used to phenotype the host response to nematode challenge. Transformation of RLP-2, a candidate resistance gene for M. arenaria integrated into a silencing construct, did not alter the resistance response of Tifguard, even though downregulation of endogenous RLP-2 expression was detected in transformed roots. It is likely that RLP-2 is not the gene conditioning M. arenaria resistance in peanut.
    No preview · Article · Apr 2014 · Plant Disease
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    ABSTRACT: Tomato spotted wilt, caused by thrips-vectored Tomato spotted wilt virus (TSWV), is a very serious problem in peanut (Arachis hypogaea L) production in the southeastern U.S. Establishment of within row plant densities of 13 or more plants/m of row of moderately resistant cultivars is recommended as part of an integrated management system for minimizing losses to spotted wilt. To achieve that plant density, growers often plant 19 or more seed/m of row. Seed costs represent a major expense for peanut producers. Reducing costs by using lower seeding rates would be desirable if it could be done without increasing risk of losses to tomato spotted wilt. Field experiments were conducted in Tifton, Georgia in 2008 and 2009 to determine whether new cultivars with improved field resistance to TSWV can allow use of lower seeding rates without increasing risk of losses to tomato spotted wilt. In each year, peanut cultivars, Georgia Green, Georgia-06G, Florida-07, and Tifguard were combined factorially with four seeding rates, 9.8, 13.1, 16.4, and 19.7 seed/m of row. Across the two years, final incidence of tomato spotted wilt and standardized area under the disease progress curve for tomato spotted wilt epidemics decreased linearly with increasing seeding rate for all cultivars. Across the two years, final incidence of tomato spotted wilt at 9.8 seed/m of row seeding rate was 55% for Georgia Green and 17% for the mean of the other three cultivars. For Georgia Green, incidence of tomato spotted wilt decreased 1.9% with each seed/m increase in seeding rate, whereas the incremental decrease was 0.8% for the mean of the other three cultivars. These results indicate that levels of field resistance to TSWV in several new cultivars are adequate to allow use of lower seeding rates than with the moderately resistant cultivar Georgia Green without increasing the risk of losses to spotted wilt.
    No preview · Article · Nov 2013 · Crop Protection

  • No preview · Article · Jul 2013 · Peanut Science
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    ABSTRACT: Peanut (Arachis hypogaea L.) is often grown in climates of intermittent drought on sandy soils. Plants expressing water-conservative traits would minimize exposure to end-of-season, severe drought. Two traits resulting in conservative transpiration rates (TRs) are limitations on TR with soil drying and with increasing vapor pressure deficit (VPD). This study focused on parents of existing recombinant inbred line (RIL) populations as sources of divergent expression of these two traits. If divergence is found, their derived RIL population could be used in identifying genetic markers. Since both water-conservation traits are laborious to document, a key extension of this study was to explore the possibility of using aquaporin inhibitors as practical tools in marker identification. Tifrunner had a lower soil water threshold for a decline in TR than NC 3033 and N08082olJCT. Tifrunner also had a higher VPD breakpoint than three genotypes, including NC 3033 and N08082olJCT. The difference between Tifrunner and these other two genotypes extended to their response to aquaporin inhibitors. The decrease in TR of Tifrunner when exposed to aquaporin inhibitors was much larger than NC 3033 when treated with silver and N08082olJCT when treated with zinc. This study indicates that an effort to develop drought markers in peanut RIL population should focus on Tifrunner x NC 3033 using the silver inhibitor and/or Tifrunner x N08082olJCT using the zinc inhibitor.
    Full-text · Article · Jun 2013 · Crop Science
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    Full-text · Article · Jun 2013 · Crop Science
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    P. Timper · D. M. Wilson · C. C. Holbrook
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    ABSTRACT: Peanut kernels are susceptible to colonization by some species of Aspergillus which, under conditions of drought and high temperatures, can produce aflatoxins prior to harvest. The objective of this research was to determine the mechanism by which the peanut root-knot nematode (Meloidogyne arenaria) increases aflatoxin contamination in peanut. Research determined 1) the role of nematode infection of roots vs. pods in increased aflatoxin contamination and 2) whether increased aflatoxin production in nematode-infected peanut is due to a greater percentage of small or immature kernels. An additional objective was to determine whether a peanut cultivar with resistance to M. arenaria would reduce the risk of preharvest aflatoxin contamination. In the greenhouse, researchers physically separated root growth from pod set and inoculated each location with M. arenaria or a water control in a 2 × 2 factorial design with 12–15 replications. Of the six trials conducted, data indicated that pod and root infection by M. arenaria was associated with elevated aflatoxin concentrations in one and three trials, respectively. This suggests that root infection by the nematode can increase aflatoxin concentrations in the peanut kernel. Another 2 × 2 factorial experiment was conducted with two peanut genotypes (Tifguard and TifGP-2) and two nematode treatments (with and without M. arenaria) with six replications. The cultivar Tifguard is resistant to M. arenaria and TifGP-2 is susceptible. The experiment was carried out in 24 field microplots equipped with a rainout shelter. The experiment was conducted five times from 2006 to 2010. Infection of TifGP-2 by M. arenaria did not lead to greater percentages of small kernels. In only one year (2007), nematodes appeared to increase the percentage of damaged kernels, though aflatoxin concentrations were not affected by nematodes in that year. In the rainout shelter experiment, 2006 was the only year where nematode infection of peanut increased aflatoxin concentrations. In that year, there were lower aflatoxin concentrations in the nematode-resistant cultivar Tifguard than the susceptible germplasm TifGP-2 (12 vs. 136 ng/g).
    Full-text · Article · Jan 2013 · Peanut Science

  • No preview · Article · Jan 2012 · Plant Health Progress

  • No preview · Chapter · Jul 2011

  • No preview · Article · Jul 2011 · Peanut Science
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    Y. Chu · C. L. Wu · C. C. Holbrook · B. L. Tillman · G. Person · P. Ozias-Akins
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    ABSTRACT: The dynamic challenges of peanut (Arachis hypogaea L.) farming demand a quick response from breeders to develop new cultivars, a process that can be aided by the application of molecular markers. With the goal to pyramid nematode resistance and the trait for high oleic: linoleic acid (high O:L) ratio in seeds, nematode-resistant cultivar Tifguard was used as the recurrent female parent and high O: L cultivars Georgia-02C and Florida-07 were used as donor parents for the high O:L trait. 'Tifguard High O/L' was generated through three rounds of accelerated backcrossing using BCnF1 progenies selected with molecular markers for these two traits as the pollen donors. Selfed BC3F2 plants yielded marker-homozygous individuals identified as Tifguard High O/L, compressing the hybridization and selection phases of the cultivar development process to less than 3 yr. The accuracy of marker-assisted selection (MAS) was confirmed by phenotyping a subset of F-2:3 populations from both parental combinations. Once additional molecular markers linked with traits of interest are designed to be compatible with high-throughput screening platforms, MAS will be more widely integrated into peanut breeding programs.
    Full-text · Article · Jul 2011 · The Plant Genome
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    ABSTRACT: Germin-like proteins (GLPs) play diversified roles in plant development and defense response. Here, we identified 36 expressed sequence tags (ESTs) encoding GLPs from peanut (Arachis hypogaea L.). After assembly, these ESTs were integrated into eight unigenes named AhGLP1 to AhGLP8, of which, three (AhGLP1-3) were comprised 14, ten, and seven EST clones, respectively, whereas the remaining ones were associated with one single clone. The length of the deduced amino acid (AA) residues ranged from 208 to 223 AAs except for AhGLP6 and AhGLP8, which were incomplete at the carboxyl terminus. All of the AhGLPs contained a possible N-terminal signal peptide that was 17 to 24 residues in length excluding AhGLP7, where there is likely a non-cleavable amino terminus. Phylogenetic analysis showed that these AhGLPs were classified into three subfamilies. Southern blot analysis indicated that AhGLP1 and AhGLP2 likely have multiple copies in the peanut genome. The recombinant mature AhGLP1 and AhGLP2 proteins were successfully expressed in Escherichia coli. The purified AhGLP2 has superoxide dismutase (SOD) activity in enzymatic assay, but not oxalate oxidase activity. The SOD activity of AhGLP2 was stable up to 70°C and resistant to hydrogen peroxide, suggesting that AhGLP2 might be a manganese-containing SOD. Furthermore, AhGLP2 could confer E. coli resistance to oxidative damage caused by paraquat, suggesting that the AhGLP2 likely protects peanut plants from reactive oxygen metabolites. Thus, information provided in this study indicates the diverse nature of the peanut GLP family and suggests that some of AhGLPs might be involved in plant defense response. KeywordsPeanut–GLP family–Superoxide dismutase–Oxalate oxidase–Disease resistance
    Full-text · Article · Jun 2011 · Plant Molecular Biology Reporter
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    ABSTRACT: In 2001, entries from the peanut core collection, a subset of the USDA peanut germplasm collection, were planted in non-replicated plots in a field with a history of Sclerotinia blight caused by Sclerotinia minor. Variability existed among entries for reaction to Sclerotinia blight. Of the 744 entries evaluated, 11% had no disease, nearly 30% had <10% disease incidence, and only 21% had 50% disease incidence or more. Most of the resistant entries had an upright growth habit and were in early and mid-maturity groups. Many of the early maturing entries were susceptible to the foliar disease pepper spot which occurred throughout the study. Entries were selected for further evaluation in replicated plots based on a nil to low (<10%) incidence of Sclerotinia blight, adaptation and/or vigor, and other desirable characteristics such as an intermediate to prostrate growth habit and pepper spot resistance. Selected entries were retested in both 2002 and 2003 (n = 62) and compared to resistant (Tamspan 90), moderately resistant (Tamrun 96), and susceptible (Okrun) reference cultivars. Most entries (55 in 2001 and 46 in 2003) had disease incidence less than Tamrun 96 and similar to Tamspan 90. In 2003 when disease incidence was highest, all 46 entries with resistant reactions similar to that of Tamspan 90 had erect plant growth habits except for entries 208 and 582 which were prostrate, and entries 273, 128, and 804 which were intermediate. Resistance to Sclerotinia blight and yield similar to Tamspan 90, plant habit, and/or reactions to pepper spot and web blotch were used to select the best entries. Entries 208, 128, 804, 582, and 273 combined resistance to Sclerotinia blight, pepper spot, and web blotch with less than erect growth habits. Entry 103 had good Sclerotinia blight resistance and yield, but an upright growth habit. Entry 92 had an upright growth habit and low yield, but good Sclerotinia blight resistance. Entries 92 and 103 had upright growth habits but were among the best entries for resistant to pepper spot and web blotch. Entries 426, 184, and 562 were upright and susceptible to pepper spot, but had resistance to web blotch and the best resistance to Sclerotinia blight. These entries appear to be useful sources of resistance to Sclerotinia blight for breeding programs and for increasing the probability of finding additional sources of resistance in clusters of germplasm identified within the entire USDA collection.
    Full-text · Article · Jan 2010 · Peanut Science

  • No preview · Technical Report · Jan 2010
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    ABSTRACT: Peanut is vulnerable to a range of foliar diseases such as spotted wilt caused by Tomato spotted wilt virus (TSWV), early (Cercospora arachidicola) and late (Cercosporidium personatum) leaf spots, southern stem rot (Sclerotium rolfsii), and sclerotinia blight (Sclerotinia minor). In this study, we report the generation of 17,376 peanut expressed sequence tags (ESTs) from leaf tissues of a peanut cultivar (Tifrunner, resistant to TSWV and leaf spots) and a breeding line (GT-C20, susceptible to TSWV and leaf spots). After trimming vector and discarding low quality sequences, a total of 14,432 high-quality ESTs were selected for further analysis and deposition to GenBank. Sequence clustering resulted in 6,888 unique ESTs composed of 1,703 tentative consensus (TCs) sequences and 5185 singletons. A large number of ESTs (5717) representing genes of unknown functions were also identified. Among the unique sequences, there were 856 EST-SSRs identified. A total of 290 new EST-based SSR markers were developed and examined for amplification and polymorphism in cultivated peanut and wild species. Resequencing information of selected amplified alleles revealed that allelic diversity could be attributed mainly to differences in repeat type and length in the SSR regions. In addition, a few additional INDEL mutations and substitutions were observed in the regions flanking the microsatellite regions. In addition, some defense-related transcripts were also identified, such as putative oxalate oxidase (EU024476) and NBS-LRR domains. EST data in this study have provided a new source of information for gene discovery and development of SSR markers in cultivated peanut. A total of 16931 ESTs have been deposited to the NCBI GenBank database with accession numbers ES751523 to ES768453.
    Full-text · Article · Feb 2009 · International Journal of Plant Genomics
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    ABSTRACT: Cylindrocladium black rot (CBR), caused by Cylindrocladium parasiticum, and root-knot nematode, Meloidogyne arenaria, both infect and cause damage to the roots of peanut. Greenhouse and microplot experiments were conducted with the runner type peanut genotypes C724-19-15, C724-19-25 and Georgia-02C with different levels of resistance to nematode and CBR to better understand the interactions between the two pathogens. In the greenhouse, inoculation of 500–3000 eggs per plant of M. arenaria did not affect the level of root rot induced by 1·0 to 5·0 microsclerotia of C. parasiticum per g soil. In microplots, the root rot ratings from Georgia-02C and C724-19-25 were higher in plots infested with M. arenaria (0·4–2·0 eggs per cm3 soil) and C. parasiticum than in plots with C. parasiticum alone; however, M. arenaria did not increase the root rot ratings on the nematode resistant C724-19-15. This was inconsistent with results in the greenhouse. Gall indices were not affected by C. parasiticum inoculations in the greenhouse or microplots. In both 2006 and 2007, a significant interaction between C. parasiticum inoculum densities and nematode level was observed on plant mortality. CBR inoculum greatly increased mortality on C724-19-25 and Georgia-02C, but not on C724-19-15, in the presence of M. arenaria. The mortality increase was more apparent at lower inoculum levels of both pathogens, but on the nematode-susceptible cultivars plant mortality was more with co-inoculations of the two pathogens than from either alone. Simultaneous inoculation with the two pathogens decreased yield of C724-19-25 and Georgia-02C as C. parasiticum inoculum levels increased, but even the largest inoculum of M. arenaria (2·0 eggs per cm3 soil) did not decrease yield of C724-19-15.
    Full-text · Article · Jan 2009 · Plant Pathology
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    ABSTRACT: Genomic spcience offers new research tools to explore the function of genes and their effects on plants and animals. Arachis hypogaea is a polyploid species of relatively recent origin and molecular analyses with technologies available in the 1980s and 1990s resulted in little progress in the cultivated species because of apparent lack of molecular variation. Large numbers of polymorphisms existing in wild Arachis species led to evolutionary and gene introgression studies. High throughput genomic sequencing technologies have greatly expanded the possibilities for investigating gene function, but techniques are sufficiently expensive that most federal funding has been directed toward model species and major crops. Peanut has lagged behind many other crops, but the number of researchers working on the species in the U.S. and internationally has greatly increased during recent years. In an effort to bring researchers who work with a number of legume crops together to discuss common goals, a national strategic planning workshop was held in 2001 which led to the U.S. Legume Crops Genomics Initiative. A second workshop was held in 2004 to develop a plan with specific objectives for cross-legume genomics research and to outline milestones for accomplishments. Specifically for peanut, a genomics strategic planning workshop was organized at Atlanta in 2004 by the American Peanut Council. A broad view of genomic science was adopted and goals were set by participants to include (a) improving the utility of genetic tools for peanut genomics research, (b) improving the efficacy of technology for gene manipulation in genomics, (c) developing a framework for assembling the peanut genetic blueprint, (d) improving knowledge of gene identification and regulation, and (e) providing bioinformatic management of peanut biological information. Teams of researchers, including molecular biologists, plant breeders, pathologists, and many other disciplines need to be developed to fully utilize the potential of genomics for peanut improvement.
    Full-text · Article · Jan 2009 · Peanut Science
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    ABSTRACT: Field experiments were conducted at Marianna, FL in 2006 and Tifton, GA in 2006 and 2007 to compare new peanut (Arachis hypogaea) cultivars to the moderately resistant cv. Georgia Green and the highly resistant cv. AP-3 for field resistance to Tomato spotted wilt virus (TSWV), genus Tospovirus, and to determine the effects of in-furrow application of phorate insecticide and use of twin-row versus single-row patterns on incidence of spotted wilt in these cultivars. Cvs. Georgia Green, AP-3, Georgia-03L, Georgia-01R, Florida-07, McCloud, and York were evaluated in all five experiments, and Tifguard was added in experiments at Tifton. All cultivars except McCloud had lower incidence of spotted wilt than Georgia Green in all experiments. McCloud was intermediate in resistance to TSWV and had lower incidence of spotted wilt than Georgia Green in four of five experiments. Use of the twin-row pattern also reduced incidence of spotted wilt in McCloud in both years. On Georgia Green, phorate reduced incidence of spotted wilt in 2007 and twin-row pattern reduced incidence in both years. Phorate had no effect on spotted wilt in AP-3, Georgia-03L, McCloud, Georgia-01R, or Tifguard in either year. Twin-row pattern reduced either final incidence or area under the disease progress curve in all cultivars in at least 1 year of the study. All of these new cultivars should reduce the risk of losses to spotted wilt compared with Georgia Green. In highly resistant cultivars, especially AP-3, York, and Tifguard, use of phorate insecticide or twin-row pattern may not be necessary, and may not provide noticeable benefit in reduction of spotted wilt or increased yield.
    Preview · Article · Sep 2008 · Plant Disease
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    W.B. Dong · T.B. Brenneman · C.C. Holbrook · A.K. Culbreath
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    ABSTRACT: Identification and utilization of peanut cultivars with resistance to Cylindrocladium black rot (CBR) is a desirable approach to manage this disease. The objectives of this study were to improve greenhouse and field screening techniques for resistance to CBR, and to evaluate the reaction of selected runner-type peanut genotypes. Georgia-02C (moderately resistant to CBR) and C-99R (CBR-susceptible) were used in comparing the effectiveness of different inoculation methods in the greenhouse. Disease development was affected by both size and density of microsclerotia in soil. Use of microsclerotia at a size of 150 to <250 µm and a density of 1 to 5 microsclerotia/g soil provided the best separation the CBR-resistant cultivar Georgia-02C and the susceptible C-99R based on root rot severity. Genotypes with varying resistance to CBR were evaluated by growth in a naturally infested field, and by inoculating plants in the field and greenhouse. Disease incidence and severity at harvest were the most effective parameters for evaluating CBR resistance in the field and greenhouse, respectively. The cultivars Georgia-02C and Georganic had the lowest disease incidence, whereas C-99R and DP-1 had the highest disease incidence in a naturally infested field in 2005 and 2006. Incidence of CBR was moderate for Georgia-01R in both years, but was inconsistent for C34-24-85. Georgia-02C and Georganic also showed partial resistance to CBR in greenhouse tests. Inoculated plants in the field had similar reaction with Georgia-02C and Georganic showing higher CBR resistance than C-99R and DP-1 in both 2006 and 2007. The root rot severities for genotypes Georgia-02C and Georganic were lower than those for C-99R and DP-1. Incidence of CBR in the naturally infested field was significantly correlated with CBR incidence in the inoculated plants in the field (r = 0.84, P 0.01), but neither was correlated with disease ratings for greenhouse experiments. Peanut genotypes are most reliably screened by inoculating plants in the field or using uniformly infested fields. Further study is needed to improve greenhouse screening procedures.
    Full-text · Article · Jul 2008 · Peanut Science