Georgia Green Research Articles

Identification of genes differentially expressed during early interactions between the stem rot fungus (Sclerotium rolfsii) and peanut (Arachis hypogaea) cultivars with increasing disease resistance levels

Sclerotium rolfsii, a destructive soil-borne fungal pathogen causes stem rot of the cultivated peanut, Arachis hypogaea. This study aimed to identify differentially expressed genes associated with peanut resistance and fungal virulence. Four peanut cultivars (A100-32, Georgia Green, GA-07W and York) with increasing resistance levels were inoculated with a virulent S. rolfsii strain to study the early plant–pathogen interaction. 454 sequencing was performed on RNAs from infected tissue collected at 4 days post inoculation, generating 225,793 high-quality reads. Normalized read counts and fold changes were calculated and statistical analysis used to identify differentially expressed genes. Several genes identified as differential in the RNA-seq experiment were selected based on functions of interest and real-time PCR employed to corroborate their differential expression. Expanding the analysis to include all four cultivars revealed a small but interesting set of genes showing colinearity between cultivar resistance and expression levels. This study identified a set of genes possibly related to pathogen response that may be useful marker assisted selection or transgenic disease control strategies. Additionally, a set of differentially expressed genes that have not been functionally characterized in peanut or other plants and warrant additional investigation were identified.

Analysis of the Discourse of Power in Etel Adnan's Play Like A Christmas Tree

This paper seeks to investigate the sources of power in the discourse of an Arab-American writer, Etel Adnan's one act play, Like a Christmas Tree . The play represents a heated argument between two figures who stand for two different ideologies and who fall within the frame of 'binary opposition' , transcultural misunderstanding, and colonial hegemony versus native resistance . Supposedly, an American Journalist, Jim, is expected to dominate the discourse by force of his cultural and professional background, but sarcastically enough, the Iraqi butcher, Badr is the part who represents power and domination throughout the play. The current paper depends on more than one tool of analysis: Norman Fairclough's (2001) and Foucault's(2004) concepts of power and discourse, Grice's theory of 'cooperative principles'(1989), Brown and Gilman's study of 'address forms' (1972), and Georgia Green's contribution in the process of 'turn-taking' (1989).The study celebrates an analysis of data which uncovers the power of discourse in the exchanges of both characters and sheds light on the identity of both of them in an attempt to affirm that 'power' is not necessarily on the side of the stronger. Keywords : discourse, power, address forms, turn-taking, interruption, topic control

Seeding Rate and Planting Date Impacts Stand Density, Diseases, and Yield of Irrigated Peanuts

Release of peanut cultivars with enhanced tomato spotted wilt (TSW) resistance along with the decline in the incidence of this disease gives Alabama producers the option of earlier planting of irrigated peanuts to optimize farm operations and lower seeding rates to reduce input costs. Mid-April and mid-May plantings of the cvs. Florida-07, Georgia-06G, and Georgia Green at 6.6, 9.8, 13.1, and 19.7 seed/m were monitored over three years for TSW, stem rot, and leaf spot diseases as well as yield. Despite low TSW pressure and lack of a seeding rate response, disease incidence was higher in Georgia Green than Florida-07 and Georgia-06G with higher TSW indices noted for the April than May plantings of the former but not latter two cultivars. While not impacted by planting date, stem rot incidence, which was higher at 13.1 and 19.7 than 6.6 seed/m, was lower on Florida-07 than Georgia-06G and Georgia Green with the latter proving most susceptible. Although leaf spot intensity was not impacted by seeding rate, disease ratings were higher for May than April plantings, with Florida-07 and Georgia-06G having lower leaf spot ratings than Georgia Green in two of three study years. While planting date did not impact yield in two of three years, higher yields were recorded at 13.1 and 19.7 than 6.6 seed/m, with Florida-07 and Georgia-06G having higher yields than Georgia Green. Accepted for publication 16 February 2015. Published 20 April 2015.

Stability of TSWV General Field Resistance in the ‘Georgia Green’ Peanut Cultivar

There are mainly two types of host-plant disease resistance. General or horizontal resistance is usually controlled by several genes each acting with minor additive effects, and specific or vertical resistance is usually controlled by one or two genes with a dominant major effect. In most cases, general resistance may not provide as high a level of control as specific; however, general type of resistance is usually more desirable for long-term stability. Therefore, the objective of this 13-year study was to determine the stability of the general disease resistance to tomato spotted wilt (TSW), caused by Tomato spotted wilt virus (TSWV), found in the peanut (Arachis hypogaea L.) cultivar ‘Georgia Green', as indicated by comparisons with the highly susceptible ‘Florunner’ cultivar. The general host-plant TSWV resistance of Georgia Green was found to have consistently lower TSW at mid-season and total disease (primarily TSW and any soilborne disease) incidence at late season, respectively, and higher pod yield compared to Florunner across all 13 years without any genotype-by-year (G×Y) interaction for these variables. Consequently, the general TSWV-resistance of Georgia Green was found to be highly stable across many years, and should be utilized for progress in breeding improved TSWV-resistant peanut cultivars. Accepted for publication 11 May 2015. Published 18 May 2015.

Mycelial Compatibility and Pathogenic Diversity Among Sclerotium rolfsii Isolates in the Southern United States.

Sclerotium rolfsii is a soilborne fungus that causes southern blight on a wide range of plants in tropical and subtropical regions of the world. Eighty-four isolates collected from Florida, Georgia, Louisiana, South Carolina, Texas, and Virginia were paired and assigned to 23 mycelial compatibility groups (MCGs), of which 11 MCGs consisted of a single isolate. Isolates within an MCG typically originated from different hosts and different geographical areas, with the exception of MCG 11. In all, 13 of the 15 isolates in MCG 11 originated from peanut in Georgia and Florida, while the other 2 isolates originated from potato in Virginia and from the ornamental Barlaeria cristata in Florida. Significant differences in the size and number of sclerotia produced in vitro existed between isolates from peanut and other hosts. Nineteen isolates representative of the most common MCGs (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 15, 16, 17, and 18) were tested for pathogenicity on tomato, pepper, and peanut. All isolates were pathogenic on all hosts but virulence differed significantly among isolates. Isolates collected from peanut were the most virulent on all three hosts compared with isolates collected from tomato and pepper. 'Georgia Green' peanut was more susceptible to peanut isolates from Georgia than to the other tested isolates. Of the two tomato entries, the commercial tomato 'Tygress' was less susceptible than the previously reported resistant breeding line 5635M to many of the S. rolfsii isolates tested, with the exception of the peanut isolates collected from Georgia. These initial findings suggest that considerable variation exists among S. rolfsii isolates throughout the southern United States, with some indications of specialization for the isolates collected from peanut.

Peanut Cultivar Response to Tomato Spotted Wilt over Five Planting Dates

ABSTRACT Tomato spotted wilt virus (TSWV) is vectored by thrips and causes an economically damaging peanut disease in the southeastern U.S. Peanut planting was traditionally initiated when soil temperatures became favorable in April. Planting in the latter two thirds of May is recommended to avoid thrips feeding and reduce tomato spotted wilt (TSW) incidence. This regime concentrates work load for growers and buying points, increases risk of tropical storm damage during harvest, and may contribute to reduced crop maturity. Improved TSW tolerance in cultivars may allow growers to plant earlier spreading risk and work load. Cultivars Georgia Green, Georgia-03L, AT 3085RO, and Flavor Runner 458 were compared with the advanced breeding line EXP 271516 based on peanut foliar condition, pod yield, and grade in 2008 and 2009 in Dawson, Georgia and Headland, Alabama. Peanuts were planted at five planting dates starting in late April through early June each year. Disease incidence was variable according to year, location, and planting date. Planting dates in April and early May resulted in higher TSW incidence. Foliar TSW ratings for the susceptible cultivar Flavor Runner 458 ranged between 48–96% at harvest. Georgia Green had 10–65% TSW incidence while maintaining yields between 3,315–5,440 kg/ha. Other cultivars had better TSW tolerance resulting in higher yield under more intense TSW pressure. Planting in the middle of May or later resulted in the highest yields. Cultivars with improved tolerance to TSW maintained yield above 4,490 kg/ha in early plantings. These results indicate the least risky management is possible by planting the most TSW tolerant genotypes during the current recommended planting dates.

Effects of seeding rate and cultivar on tomato spotted wilt of peanut

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.

Effect of Gypsum Application on Mineral Composition in Peanut Pod Walls and Seeds

ABSTRACTAlleviation of soil‐Ca deficiency through gypsum amendment increases the yield potential and ensures high seed quality in peanut (Arachis hypogaea L.). The effects of gypsum treatment, plant life cycle, and the fruit development stages on the accrual of several essential minerals (Ca, S, Mg, P, K, Cu, Ni, Mn, Zn, and Fe) and Na were studied in the pod walls and seeds of two runner cultivars, C‐99R and Georgia Green. Calcium concentration was nearly twofold higher in pod walls than in seeds, irrespective of gypsum treatment and cultivar differences. Significant increases in Ca and S, a decrease in P concentration in pod walls and seeds, and a marginal decline in seed‐Mg concentration were discernible following gypsum treatment. Sodium concentration decreased in the pod walls and Zn concentration increased in the seeds due to gypsum treatment. Progression in the plant life cycle stage was positively correlated with Ca accrual in both pod walls and seeds. The small‐seeded cultivar Georgia Green showed tissue‐specific increases in the acquisition of Ca, Mg, and Zn in pod walls and seeds, and a decrease in P concentration in the seeds compared with the large‐seeded cv. C‐99R. Compared with the respective seed maturation stages, the pod walls had lower S, Mg, P, K, and Zn, and higher Ca, Cu, Ni, Mn, Fe, and Na concentrations. While Ca, S, Mg, P, K, Zn, Fe, and Na concentrations declined, Mn concentration increased in both pod walls and seeds during fruit development.

Improvement of peanut (Arachis hypogaea L.) transformation efficiency and determination of transgene copy number by relative quantitative real-time PCR

The biolistic method is reliable for delivering genes of interest into various species, but low transformation efficiency can be a limiting factor in its application. To test various conditions that could improve peanut transformation via particle bombardment, embryogenic tissues of the peanut cultivar Georgia Green were co-bombarded with two plasmids: one containing a green fluorescent protein gene and one containing a gene of interest plus a selectable marker. The fluorescence in bombarded embryogenic tissues was measured to evaluate transformation efficiency. A 4.6-fold improvement of transformation efficiency was achieved in stably transformed peanut lines by introducing protamine instead of conventional spermidine in a bombardment mixture with 70 ng/shot plasmid DNA and 50 μg/shot gold. Unexpectedly, the reduction of plasmid DNA from 700 to 70 ng/shot produced transgenic lines with significantly increased numbers of transgene copies. To determine the transgene copy number during plantlet regeneration, relative quantitative real-time polymerase chain reaction (qPCR) was established using fluorescently labeled universal library probes. A correlation of 95% was found for estimation of copy number between Southern blot and qPCR data. Given its speed and high-throughput nature, qPCR can be employed as an effective screening tool to separate high copy number events from low copy number events as early as the shoot formation stage of regeneration.

Second Generation Peanut Genotypes Resistant to Thrips-Transmitted Tomato Spotted Wilt Virus Exhibit Tolerance Rather Than True Resistance and Differentially Affect Thrips Fitness

Spotted wilt disease caused by Tomato spotted wilt virus (TSWV) (family Bunyaviridae; genus Tospovirus) is a major constraint to peanut (Arachis hypogaea L.) production in the southeastern United States. Reducing yield losses to TSWV has heavily relied on planting genotypes that reduce the incidence of spotted wilt disease. However, mechanisms conferring resistance to TSWV have not been identified in these genotypes. Furthermore, no information is available on how these genotypes influence thrips fitness. In this study, we investigated the effects of newly released peanut genotypes (Georganic, GA-06G, Tifguard, and NC94022) with field resistance to TSWV and a susceptible genotype (Georgia Green) on tobacco thrips, Frankliniella fusca (Hinds), fitness, and TSWV incidence. Thrips-mediated transmission resulted in TSWV infection in both TSWV-resistant and susceptible genotypes and they exhibited typical TSWV symptoms. However, some resistant genotypes had reduced viral loads (fewer TSWV N-gene copies) than the susceptible genotype. F. fusca larvae acquired TSWV from resistant and susceptible genotypes indicating that resistant genotypes also can serve as inoculum sources. Unlike resistant genotypes in other crops that produce local lesions (hypersensitive reaction) upon TSWV infection, widespread symptom development was noticed in peanut genotypes. Results indicated that the observed field resistance in peanut genotypes could be because of tolerance. Further, fitness studies revealed some, but not substantial, differences in thrips adult emergence rates and developmental time between resistant and susceptible genotypes. Thrips head capsule length and width were not different when reared on different genotypes.

Evaluation of five peanut (Arachis hypogaea) genotypes to identify drought responsive mechanisms utilising candidate-gene approach.

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.

Stability Analysis of Incidence of Tomato Spotted Wilt in Virginia-Type Peanut Cultivars and Breeding Lines

ABSTRACT Tomato spotted wilt (TSW) caused by Tomato spotted wilt tospovirus (TSWV) has become a serious constraint to peanut (Arachis hypogaea L.) production in the Virginia-Carolina production area. Regression stability analysis was applied to TSW incidence data collected in 64 trials conducted over 17 years to determine if an array of 31 virginia-type cultivars and breeding lines exhibited variation in their reactions to increasing levels of general TSW intensity compared with the standard field-resistant cultivar Georgia Green and hirsuta-type line PI 576636. Eight cultivars (NC 7, NC 9, NC 10C, NC-V 11, NC 12C, Perry, Phillips, and Brantley) had mean effects greater than zero (P<0.01) while Bailey, four Bailey siblings, and N96076L, Bailey's resistant parent, all had mean effects less than zero (P<0.01). The deviations of the slope of regression on environmental index (β̂k) for four of the eight susceptible cultivars were greater than zero, indicating greater than average reaction to increased levels of TSW. The β̂k for Bailey indicated that its response to increasing levels of TSW was flat. PI 576636 was confirmed as a highly field-resistant line. The slopes of Georgia Green, the standard TSWV-resistant runner-type cultivar, the Bailey siblings and N96076L did not differ from the average of all lines. The correlation between mean effect and β̂k was r = 0.693, indicating that approximately half the variation in β̂k could be explained by mean effects. However, the regression analysis provided information useful in describing the TSW reactions of the lines and cultivars.

Effect of Cultivar, Irrigation, and Soil Calcium on Runner Peanut Response to Gypsum

Calcium is often limiting to peanut (Arachis hypogaea L.) yield, grade, and germination in the southeastern United States. The response of large‐seeded (Georgia‐06G) and small‐seeded (Georgia Green) runner peanuts to gypsum applications was evaluated in 14 tests in southern Alabama and Georgia. Experiments were conducted in a randomized complete block design with four replications of gypsum applications as main treatments (0, 560, 1120, and 1680 kg ha−1) in soils with a range of soil Ca (178–498 mg kg−1) in both irrigated and non‐irrigated tests. Increases in yield, grade, seed Ca, and germination were significant with increased gypsum application for non‐irrigated tests when data were combined. In the non‐irrigated tests, yield increases ranged from 500 to 1000 kg ha−1 and grade indicated by sound mature kernels (SMK) increased 3.4 to 5%. Critical pegging zone soil Ca values of 150 and 250 mg kg−1 were evaluated and found appropriate for irrigated and non‐irrigated peanuts, respectively. Georgia‐06G had lower seed Ca concentrations and slightly lower germination than Georgia Green. More than 95% germination of Georgia‐06G and Georgia Green was observed when seed Ca concentrations were >600 mg kg−1. Analysis of Ca concentrations in nearly mature seeds pre‐harvest may provide an indication of seed germination quality as seed Ca concentration increased at approximately the same rate as seed size from immature white to mature black peanut maturity classes using the hull‐scrape method.

Assessing Systemicity of Peanut Fungicides Through Bioassay of Plant Tissues with Sclerotium rolfsii.

To better understand movement of systemic fungicides in peanut (Arachis hypogaea), three terminal, fully expanded leaves of primary lateral branches of 'Tifrunner' peanut were treated with prothioconazole + tebuconazole (Provost, 0.29 kg a.i./ha), azoxystrobin (Abound, 0.31 kg a.i./ha), or flutolanil (Moncut, 0.79 kg a.i./ha) in field experiments. Basipetal leaves and pods on the same branch with the treated leaves were sequentially numbered from 1 to 3, with 1 being closest to treated foliage. These nontreated tissues, with newly formed terminal leaves, were sampled 4, 8, and 12 days after treatment for bioassay with Sclerotium rolfsii. All fungicides protected new acropetal leaves while prothioconazole + tebuconazole also provided some inhibition of S. rolfsii in nontreated basipetal leaves but no fungicide protected pods. In the greenhouse, applications of prothioconazole + tebuconazole or prothioconazole (Proline, 0.18 kg a.i./ha) to main stems of 'Georgia Green' provided some protection to leaves from nontreated cotyledonary branches sampled 14 days after last treatment but S. rolfsii was not inhibited on nontreated roots, stems, or pods. The results demonstrate acropetal protection by all fungicides evaluated, and indicate that prothioconazole + tebuconazole or prothioconazole applied to foliage can sometimes reduce diseases in the lower, nontreated portions of the plant.

Peanut Genotype and Seeding Rate Effects on Spotted Wilt

Establishing high plant populations helps suppress epidemics of spotted wilt, caused by Tomato spotted wilt virus (TSWV), in peanut (Arachis hypogaea L.). However, seed costs make it desirable to minimize seeding rates used. To determine whether new resistant genotypes can allow use of reduced seeding rates, field experiments were conducted at Tifton, GA, in 2008-2009 in which seven genotypes were combined factorially with two seeding rates, 9.8 and 19.7 seed/m of row. Genotypes included three cultivars (Georgia Green, Georgia-01R, and Georgia-02C) and four advanced breeding lines (GA 052524, GA 052527, GA 052529, and C724-19-25). Across years and genotypes, final incidences of spotted wilt and standardized areas under the spotted wilt disease progress curves were lower, and yields were higher in all other cultivars and breeding lines than in the moderately TSWV-resistant cultivar Georgia Green. Final incidence of spotted wilt was lower in GA 052527 and GA 052529 than in any of the cultivar standards, and yields of all four breeding lines were higher than for any of the three cultivars. Across genotypes, final incidence of spotted wilt and standardized areas under the spotted wilt disease progress curves were lower and yield was higher for the 19.8 seed/m treatment than the 9.8 seed/m. Accepted for publication 30 November 2011. Published 27 February 2012.

Interactive Effects of Fungicide, Application Timing, and Spray Volume on Peanut Diseases and Yield

Fungicide penetration of the peanut (Arachis hypogaea) canopy to target soilborne pathogens is difficult due to the dense foliage present when mid- to late-season applications are made. To assess the effect of application timing and volume on leaf spot and stem rot control as well as peanut yield, pyraclostrobin (0.21 kg a.i./ha) or chlorothalonil (1.26 kg a.i./ha), a systemic and a contact fungicide, respectively, were applied four times on cv. Georgia Green during the day (on unfolded leaves) or at night (on folded leaves) at 187, 243, or 355 liters/ha. Night application of pyraclostrobin, across spray volumes, gave the best stem rot control and pod yield increase. Pyraclostrobin applied during the day at higher spray volumes also slightly increased control of stem rot, apparently by improving canopy penetration. Neither application timing nor spray volume affected leaf spot control with pyraclostrobin. Higher spray volumes for the chlorothalonil applications tended to improve control of early and late leaf spot, possibly by increasing coverage of foliage and stems. Accepted for publication 10 January 2012. Published 20 April 2012.

Agronomic and Economic Comparisons of Double-Crop and Relay-Intercropping Systems of Peanut with Wheat

The climatic conditions of the southeastern US may allow multiple cropping systems of peanut (Arachis hypogaea L.) with wheat (Triticum aestivum L.) to be a sustainable approach toward crop production. The objectives of this project were to determine the agronomic, economic, and weed control viability of double-crop (DC) and relay-intercropping (RI) systems of peanut with wheat. Eight cropping systems including variations of DC, RI, and monocrop (MC) management as main-plots and a sub-plot effect of three peanut cultivars were assessed. Studies were conducted in Tifton, GA, in 2009 and 2011 and Plains, GA, in 2010 and 2011. Differences among yield, grade and Tomato spotted wilt virus (Tospovirus) (TSWV) incidence were significant among cropping systems and genotypes. Double-crop peanut with wheat yielded greater than the RI systems. Georgia-06G and Tifguard had improved results over Georgia Green. Sufficient weed control was attained across all treatments in 2010 and 2011 but not in the RI plots in 2009. Income above variable cost (IAVC) for the DC ($938 to $1875/ha) systems exceeded the potential of RI ($408 to $1210/ha) and most MC ($36 to $1671/ha) treatments. Growers interested in producing peanuts and wheat in the same year would be at an advantage to use a DC system.

Expansion of a direct shoot organogenesis system in peanut (Arachis hypogaea L.) to include US cultivars

Agrobacterium-mediated transformation, employing direct shoot organogenesis, allows for mature transgenic plants to be obtained quickly (3–4 mo). In this study, peanut (Arachis hypogaea L.) cultivars Florida-07, Georgia Green, Georgia Brown, New Mexico Valencia A, and VC-2 were selected to test their shoot induction response for use in future transformation experiments. Two types of cotyledon explants were examined, those that previously had an attached embryo axis upon cotyledon separation (explant A) and those that were embryo axis-free upon separation (explant B). Explants were placed onto a shoot induction medium with N6-benzyladenine concentrations ranging from 10–80 μM for Florida-07, Georgia Green, and VC-2; 10–20 μM for Georgia Brown; and 10–640 μM for New Mexico Valencia A. Following a 4-wk culture period, explants were visually rated based on a scale of 1–4, where 1 indicated slight greening, but no growth, and 4 indicated greening, adventitious bud formation, as well as small leaf expansion. A difference in shoot induction was observed for the cotyledon explants examined (P > t = t = <0.0001). Additionally, cultivars responded to the culture conditions differently (cultivar × N6-benzyladenine interaction). Georgia Green on 10 μM N6-benzyladenine produced the most shoot buds (24.6%) and the highest visual rating (2.1), followed by VC-2 on 10 μM N6-benzyladenine (22.1%, 1.8), New Mexico Valencia A on 640 μM N6-benzyladenine (21.4%, 1.8), Georgia Brown on 80 μM N6-benzyladenine (9.0%, 1.7), and Florida-07 on 40 μM N6-benzyladenine (7.1%, 1.8). Of the tested varieties, Georgia Green, New Mexico Valencia A, and VC-2 were best suited for future transformation experiments based on their shoot bud production.

Row Pattern and Seeding Rate Effects on Agronomic, Disease, and Economic Factors in Large-Seeded Runner Peanut

ABSTRACT Recent peanut cultivar releases are trending to a larger seed size, but have great resistance to tomato spotted wilt virus (TSWV). Larger-seeded cultivars cost more to plant than smaller at an equivalent population. Reduced seeding rates could save growers on seed costs and impede the spread of southern stem rot, but can reduce plant stands which can lower yields and increase TSWV incidence. Therefore, the objectives of this experiment were to compare seven peanut cultivars (Georgia Green, Georgia-06G, AT 3085RO, Florida-07, Tifguard, AP-3, and Georgia-03L) in single and twin row patterns at three seeding rates (17, 20, and 23 seed/m) on a sandy loam soil at Plains, GA for disease incidence, agronomic, and economic performance. Measured variables included yield and grade, plant height and stand, TSWV and southern stem rot incidence, and adjusted net revenue in 2008 and 2009. Twin rows outperformed single rows whenever differences occurred. The only factors consistently affected by reducing seeding rate were plant height and stand, both decreased at the lowest seeding rate. There was a trend toward lower yields (approximately 6% reduction) at the 17 seed/m rate in twin row pattern, although net returns were not diminished compared to the higher seeding rates since lower seed costs offset yield reductions. The cultivars Georgia-06G and Florida-07 had the highest yield and adjusted net revenue among the seven cultivars in both years. Tifguard and Georgia Green had lowest overall yields and would not be preferred cultivars in sandy loam soils. This study demonstrates that twin rows have higher yield, plant stands, and net revenue, plus reduced TSWV incidence than single row pattern, and a reduction in seeding rate to 17 seed/m can be made without serious risk of lost revenue. However, benefits of reducing seeding rate in twin rows were not as pronounced as they were for single rows, and exhibited a greater potential for lower yield. A grower planting in single rows would likely have the most to gain from planting fewer seed, especially under heavy southern stem rot pressure, but planting in twin rows would still be a preferred option over single rows.

Response of progeny bred from Bolivian and North American cultivars in integrated management systems for leaf spot of peanut ( Arachis hypogaea)

Early and late leaf spot (caused by Cercospora arachidicola and Cercosporidium personatum, respectively) are major yield-reducing diseases of peanut ( Arachis hypogaea L.) in the southeastern U.S. Effective suppression of both early and late leaf spot, collectively called ‘leaf spot’, can be reached with integrated disease management (IDM) systems utilizing peanut cultivars with moderate levels of resistance to these pathogens. A Bolivian landrace cultivar, Bayo Grande, and a series of progeny breeding lines were evaluated under two IDM systems consisting of various reduced application fungicide regimes and/or tillage treatments in field experiments over two years. In the absence of fungicides or when averaged across fungicide regimes, Bayo Grande and breeding lines had better leaf spot resistance when compared to cultivars Georgia Green, MDR-98 and C-99R in all experiments across years. The addition of three or four fungicide applications to Bayo Grande and several of the breeding lines suppressed leaf spot to levels similar to those genotypes and Georgia Green under the full regime. Conservation tillage reduced the need for fungicides in most genotypes in both years. Yields were higher for Bayo Grande and the breeding lines compared to Georgia Green in three of the four experiments across years. When compared across genotype, yields were greatest for the full season fungicide regime, except in 2002 when yields were similar for all treatments. Leaf spot severity was reduced in conservation tillage compared to conventional tillage in most varieties in the absence of fungicides. However, yields tended to be lower in conservation tillage treatments than in conventional tillage. Under conservation tillage, yields of Bayo Grande and two of the breeding lines were negatively impacted in one year and were overall lower in the other year. Several of these new Bolivian-derived genotypes show promise for use in a reduced fungicide and/or conservation tillage IDM system with the potential to lessen fungicide use compared to standard production practices while maintaining low leaf spot levels and high yields.