Virginia-type Cultivars Research Articles

Multilocation Evaluation of Virginia and Runner -Type Peanut Cultivars for Yield and Grade in Virginia–Carolina Region

The peanut is mostly grown in semi-arid tropical regions of the world, characterized by unpredictable rainfall amounts and distribution. Average annual precipitation in the Virginia–Carolina (VC) region is around 1300 mm; however, unpredictable distribution can result in significant periods of water deficit and subsequent reduction in yield and gross income. The development of new peanut cultivars with high yield and acceptable levels of yield stability across various water-availability scenarios is an important component of the peanut breeding program in Virginia and the Carolinas, where the large-seeded Virginia-type peanut is the predominantly grown market type. In addition, the simultaneous use of runner cultivars developed in the dryer southeastern region has been proposed as a practical solution to limited irrigation availability in the VC region. Still, the identification and adequate utilization of available commercial cultivars with the best combination of yield, drought tolerance, and gross income is more immediately beneficial to the peanut industry, yet this assessment has not been carried out to date. The aim of this study was to identify cultivars that maintain high yield and grade, therefore gross income, across a wide range of environmental conditions. We evaluated five commercially available Virginia and runner-type peanut cultivars for pod yield stability using multilocation trials over four years across 13 environments. Additive main effects and multiplicative interaction (AMMI) and different stability approaches were used to study genotype (G), environment (E), and their interaction (G × E) on pod yield. Pod yield stability was specifically assessed by using the Lin and Binn approach, Wricke’s ecovalence, Shukla’s stability, and the Finlay–Wilkinson approach. The combined analysis of variance showed highly significant effects (p ≤ 0.001) for genotypes, environments, and G × E for pod yield. The environments varied in yield (2840–8020 kg/ha). Bailey, Sullivan, and Wynne are Virginia-type cultivars. The grade factors SMK, SS, and TK changed with water regime within both market types. Among the runner cultivars, TUFRunner 297 presented high mean productivity; however, it showed specific adaptation to limited environmental conditions. Based on different stability approaches, this study concludes that Sullivan and Bailey are the most stable and adaptable cultivars across the testing environments, whereas Wynne exhibited specific adaptability to some environments. These findings have important implications for peanut cultivar recommendations in terms of meeting peanut industry standards for yield, grading quality, and breeding progress.

Pod Yield Production Among Peanut (Arachis hypogaea L.) Cultivars in South Carolina

The objective of this work was to compare peanut yield production potential for runner and Virginia market type cultivars in South Carolina. Cultivar selection decisions are integrally linked to pod yield production potential of a planted field and are often based on available historic and recent yield data. To aid farmers in this process, 24 and 27 field experiments were conducted in South Carolina between 2015 and 2020 for runner and Virginia type cultivars, respectively, to examine yield production potential. Top grouping runner type cultivars consisted of Georgia-16HO, FloRun 331, TUFRunner 297, and Georgia-12Y. Virginia type cultivars within the statistical grouping with the greatest yield included Walton and Bailey II. Total sound mature kernels among runner type cultivars was greatest for Georgia-16HO and Georgia-06G, followed by TUFRunner 297, Georgia-14N, TUFRunner 511, and Georgia-18RU. Virginia type cultivars did not significantly vary with regard to total sound mature kernels in this study. Results generated from this work may be useful as a reference to help inform cultivar selection decisions.

Relative Tomato Spotted Wilt Incidence and Field Performance among Peanut Cultivars as Influenced by Different Input Production Practices in Georgia.

ABSTRACT During 2017-19, 30 replicated yield trials were conducted to determine relative tomato spotted wilt (TSW) incidence and general field performance among 19 runner and virginia market type peanut (Arachis hypogaea L.) cultivars. Four different input production practices were compared across three Georgia locations (Tifton, Plains, and Midville). Two early-planted (April) field tests were conducted at Tifton and Plains each year. One early-planted trial involved maximum-input practices of recommended pesticides with irrigation, and the other early-planted field trial did not receive any fungicides, insecticides, or irrigation. Early-planted maximum-input production practices with irrigation resulted in the highest percentage of mid-season TSW and late-season total disease incidences while also producing the highest pod yields and dollar values. Two other optimum-planted (May) maximum-input field tests were conducted at Tifton, Plains, and Midville, GA as part of the official statewide variety trials (OVT). These OVT utilized maximum-input production practices of pesticides both with and without irrigation. In the OVT, midseason TSW incidence showed no difference between irrigated and non-irrigated; however, the end-of-season total disease percentages which were predominantly TSW did show significantly higher disease percentage, produced the highest pod yields and dollar values within the irrigated field tests compared to the non-irrigated tests. In the overall four tests comparison, disease results showed significantly lower TSW incidence in the early-planted tests without fungicides and insecticides input production practices and no-irrigation; whereas, both optimum planted OVT(s) had the lowest total disease incidence. Overall average field performance for pod yields and dollar values were significantly highest in the optimum-planted tests with maximum-inputs including irrigation. Significant differences were also found among the 19 peanut cultivars. ‘Georgia-06G', ‘Georgia-12Y', and ‘Georgia-18RU' had the lowest relative TSW incidence compared to the other runner-type cultivars. ‘Georgia-19HP' had the lowest TSW incidence and total disease incidence among the virginia-type cultivars. Among the runner cultivars, Georgia-12Y had the lowest total disease incidence at the end of the season. The highest pod yields were found with Georgia-06G and ‘Georgia-16HO'; whereas, Georgia-18RU and Georgia-06G had the highest dollar values among the runner-type peanut cultivars. Georgia-19HP had the highest pod yield and dollar value among the virginia-type cultivars.

Identification of consistent QTL for time to maturation in Virginia-type Peanut (Arachis hypogaea L.)

BackgroundTime-to-maturation (TTM) is an important trait contributing to adaptability, yield and quality in peanut (Arachis hypogaea L). Virginia market-type peanut belongs to the late-maturing A. hypogaea subspecies with considerable variation in TTM within this market type. Consequently, planting and harvesting schedule of peanut cultivars, including Virginia market-type, need to be optimized to maximize yield and grade. Little is known regarding the genetic control of TTM in peanut due to the challenge of phenotyping and limited DNA polymorphism. Here, we investigated the genetic control of TTM within the Virginia market-type peanut using a SNP-based high-density genetic map. A recombinant inbred line (RIL) population, derived from a cross between two Virginia-type cultivars ‘Hanoch’ and ‘Harari’ with contrasting TTM (12–15 days on multi-years observations), was phenotyped in the field for 2 years following a randomized complete block design. TTM was estimated by maturity index (MI). Other agronomic traits like harvest index (HI), branching habit (BH) and shelling percentage (SP) were recorded as well.ResultsMI was highly segregated in the population, with 13.3–70.9% and 28.4–80.2% in years 2018 and 2019. The constructed genetic map included 1833 SNP markers distributed on 24 linkage groups, covering a total map distance of 1773.5 cM corresponding to 20 chromosomes on the tetraploid peanut genome with 1.6 cM mean distance between the adjacent markers. Thirty QTL were identified for all measured traits. Among the four QTL regions for MI, two consistent QTL regions (qMIA04a,b and qMIB03a,b) were identified on chromosomes A04 (118680323–125,599,371; 6.9Mbp) and B03 (2839591–4,674,238; 1.8Mbp), with LOD values of 5.33–6.45 and 5–5.35 which explained phenotypic variation of 9.9–11.9% and 9.3–9.9%, respectively. QTL for HI were found to share the same loci as MI on chromosomes B03, B05, and B06, demonstrating the possible pleiotropic effect of HI on TTM. Significant but smaller effects on MI were detected for BH, pod yield and SP.ConclusionsThis study identified consistent QTL regions conditioning TTM for Virginia market-type peanut. The information and materials generated here can be used to further develop molecular markers to select peanut idiotypes suitable for diverse growth environments.

Rainout Shelter-Induced Water Deficit Negatively Impacts Peanut Yield and Quality in a Sub-Humid Environment

ABSTRACT Water deficit significantly reduces yield potential of peanut (Arachis hypogaea L.) worldwide. Availability of drought tolerant cultivars is essential, but their selection is difficult, in particular in environments where rainfall is unpredictable. This study investigated the response of eleven peanut genotypes to three water regimes and was aimed to determine if use of rainout shelters is a reliable selection method for drought tolerance in a sub-humid environment with unpredictable rainfall pattern. Water regimes were achieved by covering the plots from mid-July to early Sep with the rainout shelters and irrigating the plots to pre-determined levels: well-watered (WW) regime received full irrigation of 40 mm weekly, moderate deficit (MD) 17 mm weekly, and severe deficit (SD) only 40 mm in one “survival” irrigation in late Aug. Results showed that MD and SD reduced yield and grade for all genotypes. Compared with WW, economic value of all genotypes was 24% less under MD and 68% less under SD. Small seeded runner cultivars, ‘Florida 07′ and ‘Georgia 06G', had higher yield and grade than Virginia-type cultivars under deficit irrigation, in particular under SD. Among the Virginia-type, ‘Sugg' had highest yields under SD but was out yielded by ‘Bailey' and ‘Phillips' under MD. ‘Wynne' and ‘Spain' are the largest seeded Virginia-type cultivars; they performed poorest for yield and grade. The relative proportion of oleic fatty acid (C18:1) was less under SD compared to WW; and linoleic fatty acid (C18:2) and total saturated oils were more, but intensities depended on the genotype. Finally, the rainout setting provided comparative results with real farm peanut production in the region; this is important for breeding programs in Virginia and Carolinas, where rainfall unpredictability does not allow for drought screening in an open field setting.

Resistance to Thrips in Peanut and Implications for Management of Thrips and Thrips-Transmitted Orthotospoviruses in Peanut.

Thrips are major pests of peanut (Arachis hypogaea L.) worldwide, and they serve as vectors of devastating orthotospoviruses such as Tomato spotted wilt virus (TSWV) and Groundnut bud necrosis virus (GBNV). A tremendous effort has been devoted to developing peanut cultivars with resistance to orthotospoviruses. Consequently, cultivars with moderate field resistance to viruses exist, but not much is known about host resistance to thrips. Integrating host plant resistance to thrips in peanut could suppress thrips feeding damage and reduce virus transmission, will decrease insecticide usage, and enhance sustainability in the production system. This review focuses on details of thrips resistance in peanut and identifies future directions for incorporating thrips resistance in peanut cultivars. Research on thrips–host interactions in peanut is predominantly limited to field evaluations of feeding damage, though, laboratory studies have revealed that peanut cultivars could differentially affect thrips feeding and thrips biology. Many runner type cultivars, field resistant to TSWV, representing diverse pedigrees evaluated against thrips in the greenhouse revealed that thrips preferred some cultivars over others, suggesting that antixenosis “non-preference” could contribute to thrips resistance in peanut. In other crops, morphological traits such as leaf architecture and waxiness and spectral reflectance have been associated with thrips non-preference. It is not clear if foliar morphological traits in peanut are associated with reduced preference or non-preference of thrips and need to be evaluated. Besides thrips non-preference, thrips larval survival to adulthood and median developmental time were negatively affected in some peanut cultivars and in a diploid peanut species Arachis diogoi (Hoehne) and its hybrids with a Virginia type cultivar, indicating that antibiosis (negative effects on biology) could also be a factor influencing thrips resistance in peanut. Available field resistance to orthotospoviruses in peanut is not complete, and cultivars can suffer substantial yield loss under high thrips and virus pressure. Integrating thrips resistance with available virus resistance would be ideal to limit losses. A discussion of modern technologies such as transgenic resistance, marker assisted selection and RNA interference, and future directions that could be undertaken to integrate resistance to thrips and to orthotospoviruses in peanut cultivars is included in this article.

Combination of Disease Resistance, Drought Tolerance, and Dollar Value among Runner and Virginia-Type Peanut Cultivars in Georgia.

ABSTRACT With increasing production cost, southeast U.S. peanut (Arachis hypogaea L.) growers are continually seeking to lower inputs to enhance economical return and sustainability of their farming operation. Utilization of peanut cultivars with the best combination of disease resistance, drought tolerance, and greatest dollar value return would be beneficial. Fifteen peanut cultivars were evaluated for 5-years (2011–15) and seventeen cultivars were evaluated for 4-years (2012–15) with minimum inputs and without irrigation at two locations in Georgia. Each year, minimum inputs for disease control included only three fungicide sprays at recommended rates on a 28 d schedule beginning 37 d after planting. No insecticide, nematocides, miticides, or irrigation were applied during the growing seasons each year. ‘Georgia-06G', ‘Georgia-12Y', ‘Georgia-13M', ‘Georgia-14N', and Florida-EP ‘113’ had the lowest TSWV and total disease incidence (disease resistance) among the ten runner-type cultivars for both Georgia locations; whereas, ‘Bailey', ‘Georgia-08V', and ‘Georgia-11J' had the least disease incidence among the five virginia-type cultivars. Similarly, Georgia-13M, Georgia-06G, and Georgia-12Y had the greatest gross dollar value return per hectare (drought tolerance) among the runner-types; whereas, Georgia-08V and Georgia-11J had the greatest dollar values per hectare among the virginia-type cultivars at both Georgia locations in this four and five-year study, respectively.

Differences in Development of Oleic and Linoleic Acid in High- and Normal-Oleic Virginia and Runner-Type Peanuts

ABSTRACT A consistent, pure supply of high-oleic (HO) peanuts is important to certain segments of the food industry as it allows for the production of confections and other products with improved shelf-life characteristics. Peanut shellers have struggled with food industry demands for lots which contain greater than 95% high-oleic peanuts. Normal-oleic (NO) and HO cultivars of virginia and runner market type peanuts were grown during the 2012 and 2013 growing season respectively to investigate differences in fatty acid development between HO and NO peanuts. Fatty acid profiles of individual seeds from individual plants taken across the growing season were determined in relation to seed fresh weight. Fatty acid profiles of HO virginia-type seeds from the early sampling date of 78 days after planting (DAP) revealed oleic acid to linoleic acid ratios (O/L) of only 4.0 in the seeds of the greatest fresh weight. As the oleic acid concentration in many of the HO virginia-type peanuts reached 60 to 80% and the linoleic acid concentrations ranged from less than 1.0 to 10 % by the middle sampling date (106 DAP), the O/L ratios of most HO seeds were well above the industry accepted cut-off ratio of 9.0. A similar change in the fatty acids was seen in the HO runner cultivar. Increases in oleic acid and decreases in linoleic acid contents occurred in conjunction with the increased seed fresh weights. The data indicate that HO seed attain high-oleic status as physiological development progresses as seen in the changing seed fresh weight. However at the final sampling dates which corresponded to the harvest dates, O/L ratios of less than 9.0 were still present for the HO cultivars of both market types despite the fresh weight of some seeds being of potential marketable size. It was concluded that some of the perceived contamination of HO seed lots with NO seed could be the result of normal peanut development, especially in the virginia-type cultivar with the larger sized seeds.

Effect of Production Environment on Seed Quality of Normal and High-Oleate Large Seeded Virginia-Type Peanut (Arachis hypogaea L.)

ABSTRACT Six Virginia-type peanut (Arachis hypogaea L.) cultivars and their paired backcross-derived high-oleate lines were grown during 2003 and 2004 in North Carolina to compare standard germination (SG), cool germination (CG), and electrical conductivity (EC) of seed. Oleic acid level had no influence on SG but did alter CG and EC compared to the corresponding normal oleate cultivars. Averaged across background genotypes, high-oleate lines had lower seed vigor than their paired lines with normal oleic content. The high-oleate lines of three of the six pairs had lower CG and higher EC. Planting and harvest date affected all the seed quality traits measured. Standard germination of both normal and high-oleate lines was reduced in 2004 when harvest was delayed, but was not affected in 2003. In 2003, CG of the high-oleate lines was lower than that of normal lines in three of the four production environments; EC was higher in the high-oleate lines in all planting date and harvest date combinations. In 2004, there was no difference between the CG of normal and high-oleate lines, but EC was higher in the high-oleate lines for three of the four environments. In the greenhouse, the Virginia-type cultivars NC-V 11 and Gregory, along with their paired backcross-derived high-oleate lines were compared at 22/18 C, 26/22 C and 30/26 C day/night temperature regimes. Seed oleic to linoleic acid (O/L) ratio of normal peanut grown in 30/26 C, 26/22 C, and 22/18 C, measured 1.9, 1.5, and 1.3, respectively. The O/L ratio for their high-oleate pairs decreased from 24.7 when grown in 30/26 C to 15.9 in 26/22 C and to 13.7 in 22/18 C. Temperature did not affect the fatty acid composition of axis total lipid or phospholipid fractions. The high-oleate trait was expressed in the axis lipids. The average O/L ratio of axes from normal peanut was 1.1 while that of high-oleate lines was 4.6. Likewise, axis phospholipids for normal and high-oleate lines were 1.0 and 5.9. A lower production environment temperature decreased the O/L ratio of seed oil of high-oleic peanut lines, and the high-oleate trait expressed in peanut seed storage lipids is also expressed in axis membrane lipids to a lesser degree.

Yield performance and pest resistance among peanut genotypes when grown without fungicides or insecticides

Yield trials without fungicides or insecticides were conducted four consecutive years (2007–10) at the University of Georgia, Coastal Plain Experiment Station, Tifton Campus to evaluate for peanut (Arachis hypogaea L.) pest resistance. The most endemic diseases in the southeast U.S. are tomato spotted wilt (TSW) caused by Tomato spotted wilt virus, white mold (WM) caused by Sclerotium rolfsii Sacc, and both early and late leaf spot caused by Cercospora arachidicola Hori and Cercosporidium personatum (Berk & Curt.) Deighton, respectively. The most endemic insects are tobacco thrips (Frankliniella fusca Hinds) and potato leafhopper (Empoasca fabae Harris). Results from these replicated field tests showed significant differences (P ≤ 0.05) among advanced Georgia breeding lines and cultivars. Three Georgia cultivars ‘Georgia-01R’, ‘Georgia-05E’, and ‘Georgia-10T’ consistently produced among the best yields with high levels of resistance to TSW, white mold, leafhoppers, and leaf spot each year. Georgia-01R is a multiple-pest-resistant, runner-type cultivar with late maturity; whereas, Georgia-05E is a multiple-pest-resistant, virginia-type cultivar with medium-late maturity. Georgia-10T is a new runner-type cultivar with high level of TSWV and white mold resistance and late-maturity, similar to Georgia-01R, one of its parents. However, Georgia-10T does not appear to have the high level of leaf spot and leafhopper resistance as Georgia-01R, but it still had high yields in the absence of fungicides or insecticides.

Comparison of Virginia and Runner-Type Peanut Cultivars for Development, Disease, Yield Potential, and Grade Factors in Eastern Virginia

ABSTRACT Peanut (Arachis hypogaea L.) is an important crop in the Virginia-Carolina (VC) region. Virginia-type cultivars are preferred vs. other peanut types because of the in-shell and gourmet markets that evolved in the VC region around this peanut type. Reduced federal support coupled with increased production costs for the virginia-type peanut vs. other peanut types and recently higher fuel and pesticide prices are good reasons for farmers to consider growing other peanut types than virginia-type in the VC region. Earlier research suggested that runner-type peanut can provide yield, gross value, and economic return similar with virginia-type when grown in the VC region. However, direct comparison of runner and virginia-type cultivars needs to be updated as new cultivars become available. In this study we compared four runner-types with five virginia-type cultivars for plant development, disease incidence, pod yield, pod brightness, grade factors, and gross value in 2009 and 2010. In agreement with earlier findings, the results show that runner-types can provide similar gross returns with virginia-type peanut cultivars when grown in the northern VC region. Florida 07 runner and Bailey virginia-type, currently the most popular cultivars in the VC region, had high yields and gross values in both years. However, Florida 07 and other runners matured later and pods were less bright when compared with the virginia-types. Therefore, growing runners in the northern VC region may be challenging due shorter seasons and reduced pod brightness if peanut is used for in-shell markets.

Genotypic effect of ahFAD2 on fatty acid profiles in six segregating peanut (Arachis hypogaea L) populations

BackgroundFatty acid composition of oil extracted from peanut (Arachis hypogaea L.) seed is an important quality trait because it may affect the flavor and shelf life of resulting food products. In particular, a high ratio of oleic (C18:1) relative to linoleic (C18:2) fatty acid (O/L ≥ 10) results in a longer shelf life. Previous reports suggest that the high oleic (~80%) trait was controlled by recessive alleles of ahFAD2A and ahFAD2B, the former of which is thought to have a high frequency in US runner- and virginia-type cultivars. Functional mutations, G448A in ahFAD2A and 442insA in ahFAD2B eliminate or knock down desaturase activity and have been demonstrated to produce peanut oil with high O/L ratios. In order to employ marker assisted selection (MAS) to select a high oleic disease resistant peanut and to evaluate genotypic and phenotypic variation, crosses were made between high oleic (~80%) and normal oleic (~50%) peanuts to produce segregating populations.ResultsA total of 539 F2 progenies were randomly selected to empirically determine each ahFAD2 genotype and the resulting fatty acid composition. Five of the six crosses segregated for the high oleic trait in a digenic fashion. The remaining cross was consistent with monogenic segregation because both parental genotypes were fixed for the ahFAD2A mutation. Segregation distortion was significant in ahFAD2A in one cross; however, the remaining crosses showed no distortion. Quantitative analyses revealed that dominance was incomplete for the wild type allele of ahFAD2, and both loci showed significant additive effects. Oleic and linoleic acid displayed five unique phenotypes, based on the number of ahFAD2 mutant alleles. Further, the ahFAD2 loci did exhibit pleiotropic interactions with palmitic (C16:0), oleic (C18:1), linoleic (C18:2) acids and the O/L ratio. Fatty acid levels in these progeny were affected by the parental genotype suggesting that other genes also influence fatty acid composition in peanut. As far as the authors are aware, this is the first study in which all of the nine possible ahFAD2 genotypes were quantitatively measured.ConclusionsThe inheritance of the high oleic trait initially was suggested to be controlled by dominant gene action from two homoeologous genes (ahFAD2A and ahFAD2B) exhibiting complete recessivity. Analyzing the ahFAD2 genotypes and fatty acid compositions of these segregating peanut populations clearly demonstrated that the fatty acid contents are quantitative in nature although much of the variability in the predominant fatty acids (oleic, linoleic, and palmitic) is controlled by only two loci.

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.

Disease and Insect Assessment of Candidate Cultivars for Potential Use in Organic Peanut Production

Abstract Interest in organic peanut (Arachis hypogaea L.) production is increasing in the United States. Disease and insect resistant cultivars will be needed to meet the challenge of producing peanuts without conventional pesticides. No-fungicide and no-insecticide field trials were conducted under irrigation four consecutive years (2003–06) at the University of Georgia, Coastal Plain Experiment Station to evaluate peanut genotypes for pest resistance. The most important foliar peanut diseases in the southeast are tomato spotted wilt (TSW) caused by Tomato spotted wilt virus and both early and late leafspots caused by Cercospora arachidicola Hori and Cercosporidium personatum (Berk. & Curt.) Deighton, respectively. Two of the most important insect pests on peanut are tobacco thrips (Frankliniella fusca Hinds) and potato leafhopper (Empoasca fabae Harris). Results from these no-fungicide and no-insecticide field trials showed significant differences (P ≤ 0.05) in pest resistance among advanced Georgia breeding lines and cultivars. Two Georgia cultivars ‘Georgia-01R’ and ‘Georgia-05E’ consistently produced the highest yields and had high levels of resistance to TSW, leafhoppers, and leafspots each year. Georgia-01R is a multiple-pest-resistant, mid-oleic, runner-type cultivar; whereas, Georgia-05E is a multiple-pest-resistant, high-oleic, virginia-type cultivar. Both cultivars should be considered as good candidates for potential use in organic peanut production.

A Site-Specific, Weather-Based Disease Regression Model for Sclerotinia Blight of Peanut.

In North Carolina, losses due to Sclerotinia blight of peanut, caused by the fungus Sclerotinia minor, are an estimated 1 to 4 million dollars annually. In general, peanut (Arachis hypogaea) is very susceptible to Sclerotinia blight, but some partially resistant virginia-type cultivars are available. Up to three fungicide applications per season are necessary to maintain a healthy crop in years highly favorable for disease development. Improved prediction of epidemic initiation and identification of periods when fungicides are not required would increase fungicide efficiency and reduce production costs on resistant and susceptible cultivars. A Sclerotinia blight disease model was developed using regression strategies in an effort to describe the relationships between modeled environmental variables and disease increase. Changes in incremental disease incidence (% of newly infected plants of the total plant population per plot) for the 2002-2005 growing seasons were statistically transformed and described using 5-day moving averages of modeled site-specific weather variables (localized, mathematical estimations of weather data derived at a remote location) obtained from SkyBit (ZedX, Inc.). Variables in the regression to describe the Sclerotinia blight disease index included: mean relative humidity (linear and quadratic), mean soil temperature (quadratic), maximum air temperature (linear and quadratic), maximum relative humidity (linear and quadratic), minimum air temperature (linear and quadratic), minimum relative humidity (linear and quadratic), and minimum soil temperature (linear and quadratic). The model explained approximately 50% of the variability in Sclerotinia blight index over 4 years of field research in eight environments. The relationships between weather variables and Sclerotinia blight index were independent of host partial resistance. Linear regression models were used to describe progress of Sclerotinia blight on cultivars and breeding lines with varying levels of partial resistance. Resistance affected the rate of disease progress, but not disease onset. The results of this study will be used to develop site- and cultivar-specific spray advisories for Sclerotinia blight.

Genotypic Variation in Roasted Peanut Flavor Quality Across 60 Years of Breeding1

Abstract In developing new peanut (Arachis hypogaea L.) breeding lines and cultivars, the breeder's primary focus is upon those heritable characteristics with direct, measurable effects. Flavor quality characteristics are heritable but do not have a directly measurable economic value, so they are often overlooked. Failure to monitor and evaluate flavor quality may lead to serious defects in new breeding lines and cultivars. Flavor quality data on lines developed since 1930 were examined to identify trends in flavor quality of the cultivars and breeding populations in the virginia, runner, and fastigiate market types. Virginia-type cultivars have trended toward poorer roasted peanut flavor (reduced intensity of the roasted peanut and sweet attributes and increased intensity of the bitter attribute). Use of the commercially successful cultivars Florigiant and NC 7 in the ancestry of new breeding lines appears to have reduced the flavor quality. Runner-type cultivars increased slightly in average sweetness over time, but there has been an increase in the variance of roasted peanut intensity in the breeding population since 1980. Introgression of disease-resistant germplasm into the breeding populations appears to have had a detrimental effect on the flavor of lines in the runner and virginia market types. Use of Florunner, a multiline cultivar with a superior flavor profile, as a parent of breeding lines has contributed to generally superior flavor in the runner market type. The gains possibly could have been greater had one of Florunner's better-tasting components been used consistently in crossing programs. The limited sample of fastigiate lines and cultivars in this study showed consistent improvement in the intensities of roasted peanut and bitter attributes. Spanish-type cultivars showed improvement in the sweet attribute.

Collar Rot of Peanut Caused by Lasiodiplodia theobromae.

In August and September of 1993, a collar rot disease of peanut was observed in several fields in Virginia and North Carolina. Only a few scattered plants exhibited symptoms and signs of the disease in Southampton County and Suffolk, Virginia, and Northampton County, North Carolina. The disease was severe at two farm sites in Dinwiddie County, Virginia where the affected areas exceeded 0.4 ha in size. Numerous plants were either chlorotic, wilted, or dead. Symptomatic plants exhibited blackened stem cankers and pods. Diseased stems and tap roots were easily shredded to reveal slate-gray to black internal tissues. Black, erumpent pycnidia were observed on stem lesions at the soil surface. Immature conidia were single-celled and hyaline. Mature conidia were two-celled and dark brown. Morphological features of the fungus on diseased plants and potato dextrose agar were consistent with descriptions of Lasiodiplodia theobromae (Diplodia gossypina). The fungus was isolated from discolored seed and asymptomatic seed from fields having plants which exhibited severe symptoms. Seed treatment with captan 1.125 g + pentachloronitrobenzene 0.375 g + carboxin 0.25 g a.i./kg reduced recovery of the fungus from seed, but did not eradicate the pathogen. This treatment on naturally infested seed provided significant early-season disease suppression and improved yield significantly in 1994. Season-long disease suppression and a significant yield increase were obtained in plots planted to fungicide-treated, commercial seed from non-infested fields. At-plant and mid-season applications of fungicides in 1994 and 1995 did not improve disease suppression over that of fungicide-treated, commercial seed. Overall, Virginia-type cultivars of peanut were more susceptible to collar rot than runner-type cultivars. Among the Virginia-type cultivars, NC-V 11 exhibited moderate susceptibility and the 79-X breeding line from Florida exhibited resistance. Georgia Browne and Southern Runner were the most resistant of the runner-type cultivars.

Studies on Morphological and Physiological Aspects of the Yield Differences Between Peanut (Arachis hypogaea L.) Botanical Varieties

Six peanut (Arachis hypogaea L.) cultivars representing Virginia, Spanish and Valencia subspecies var. hypogaea, var. vulgaris and var. fastigiata, respectively, were experimented in 1993 and 1994 on the experiment field of Akdeniz University, Agriculture Faculty, Field Crops Department in Antalya to determine seasonal dry matter accumulation and dry matter partitioning, leaf area index (LAI) development, reproductive efficiency estimated by harvest index (HI), nodüle production and some pod and seed characters. Results from this study indicated that differences in partitioning of total dry matter between vegatative and reproductive organs explained most of the yield differences between cultuvars Virginia type cultivars accumulated more root, leaf and pod dry matter than other type cultivars during the growth and development stages. Valencia cultivar had the least yield capapility by accumulation more assimilat in the vegetative organs (stems) than reproductive organs (pods). Virginia type cultivars produced at least 50% greater nodule mass than Spanish and Valencia type cultivars.

Laboratory and Field Evaluations of Virginia-Type Peanut Genotypes for Resistance toDiabrotica undecimpunctata howardiBarber (Coleoptera: Chrysomelidae)

Abstract The southern corn rootworm (Diabrotica undecimpunctata howardi Barber) is the primary soil insect pest of peanut (Arachis hypogaea L.) in Virginia and North Carolina. The majority of acreage is planted to recently released cultivars which have not been extensively screened for rootworm resistance. The objectives of this study were to evaluate five virginia-type cultivars (NC-V 11, VA-C 92R, VA 93B, NC 10C, and AgraTech VC-1) and 19 breeding lines for resistance to southern corn rootworm and develop efficient resistance laboratory and field screening techniques for peanut. Laboratory-grown seedlings and pegs, and immature and mature pods taken from field-grown plants were used in bioassays. Neonates from a laboratory colony were reared to the adult stage on plant tissues and evaluated for mortality. Pod damage was determined from field studies where plants were exposed to natural southern corn rootworm infestations. With seedling feeding, NC 6 resulted in significantly more rootworm mortality as c...

Effect of drought during pod filling on utilization of water and on growth of cultivars of groundnut ( Arachis hypogaea L.)

Cultivars of groundnut ( Arachis hypogaea L.) were grown well watered or well watered except for a period during pod filling when water was withheld. When water was withheld from 84 days after sowing (DAS) to maturity, pod and seed yield was reduced by 30% in the Virginia type cultivars (Virginia Bunch and Robut-33) and by 45% in a Spanish type cultivar, McCubbin. The Virginia type cultivars also extracted water from a greater depth. Robut-33, a cultivar with a high harvest index (HI), produced the greatest yield under both well-watered and water-stressed conditions. In all cultivars, potential pod number (PN) had been almost achieved prior to the start of the period of water deficit. However, low pod number (apparently through abscission of the youngest pods), rather than small pod size, was mainly responsible for the decrease in yield. Part of the yield advantage of Robut-33 lay in initiating a large number of pods prior to the period of water deficit. This greater synchrony of development compared with the other Virginia type cultivar (Virginia Bunch) created a greater sink for assimilate prior to the period of water deficit. During the first 3 weeks of the period of water deficit, Robut-33 also had the highest crop growth rate (CGR) and was thus able to produce the most pod biomass. The characteristics of early and rapid pod growth and high HI were more important in determining yield under this water deficit than was the amount of water extracted from the soil.