Barry L. Tillman

High Levels of Field Resistance to Tomato spotted wilt virus in Peanut Breeding Lines Derived from hypogaea and hirsuta Botanical Varieties

Tomato spotted wilt, caused by Tomato spotted wilt tospovirus (TSWV) is a major problem in peanut (Arachis hypogaea L.) producing areas of the southeastern U.S. The integrated program used to manage spotted wilt relies heavily on cultivars with field resistance to TSWV, and finding new sources and greater levels of resistance to TSWV is highly desirable. Field tests were conducted in 2003 and 2004 in Marianna, FL and Tifton, GA to compare three peanut breeding lines, F NC94022-1-2-1-1-b3-B, C 11-2-39, and C 11-186 to that of standard moderately resistant cultivar Georgia Green for field response to TSWV. F NC94022-1-2-1-1-b3-B was of particular interest because it was developed from a cross between lines of A. hypogaea subsp. hypogaea var. hirsuta Kohler and A. hypogaea subsp. hypogaea var. hypogaea. In all tests, final spotted wilt ratings for breeding lines F NC94022-1-2-1-1-b3-B, C 11-2-39, and C 11-186 were lower and pod yields were higher than for Georgia Green. In three tests, final spotted wilt intensity ratings did not differ among F NC94022-1-2-1-1-b3-B, C 11-2-39, and C 11-186. At Marianna in 2004, spotted wilt intensity ratings were lower and pod yields were higher in F NC94022-1-2-1-1-b3-B than in any other entry. The high level of field resistance to TSWV in F NC94022-1-2-1-1-b3-B is presumably derived from its hirsuta type parent, PI 576638.

Response of New Field-Resistant Peanut Cultivars to Twin-Row Pattern or In-Furrow Applications of Phorate for Management of Spotted Wilt

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.

Calcium dependent protein kinase (CDPK) expression during fruit development in cultivated peanut (Arachis hypogaea) under Ca2+-sufficient and -deficient growth regimens

Adequate soil calcium (Ca²⁺) levels are crucial for sustained reproductive development of peanut (Arachis hypogaea). A role for calcium dependent protein kinase was evaluated during peanut fruit development under sufficient and deficient soil Ca²⁺ conditions. Quantitative RT-PCR and protein gel blot analyses confirmed transcriptional upregulation of CDPK in seeds developing under inadequate soil Ca²⁺ regimen, as well as spatiotemporal regulation of CDPK expression during early mitotic growth and later during the storage phase of seed development. However, a consistent basal level of CDPK was present during similar developmental stages of pod tissue, irrespective of the soil Ca²⁺ status. Immunolocalization data showed CDPK decoration primarily in the outer most cell layers of the pericarp and around vascular bundles linked by lateral connections in developing pods, as well as the single vascular trace supplying nutrients to the developing seed. Finally, carbohydrate analyses and qRT-PCR data are provided for peanut genes encoding enzymes involved in sucrose cleavage (orthologs of Vicia faba, VfCWI1 and VfCWI2) and utilization (AhSuSy and AhSpS), and oleosin gene transcripts (AhOleo17.8 and AhOleo18.5) validating a role for CDPK in the establishment and maintenance of sink strength, and subsequent onset of storage product biosynthetic phase during seed maturation.

Development and Phenotyping of Recombinant Inbred Line (RIL) Populations for Peanut (Arachis hypogaea)

ABSTRACT The identification of molecular markers for economically significant traits should greatly improve the speed and efficiency of all peanut (Arachis hypogaea L.) breeding programs. Developme...

Impact of Seed Storage Environment on Field Emergence of Peanut (Arachis hypogaea L.) Cultivars

Abstract Late-maturing peanut cultivars including DP-1, C-99R, Hull, Georgia-01R, and Florida MDR-98 (Arachis hypogaea L.) have improved resistance to late leaf spot, white mold, and tomato spotted wilt virus. The improved disease resistances offer potential cost savings for farmers. However, poor field emergence resulted in unacceptable plant stands and caused commercial seed companies to stop producing Florida MDR-98, DP-1, and Hull even though germination tests usually showed acceptable germination. Reduced field emergence seldom occurs when seed of these cultivars is grown, harvested, and stored in small batches in research storage facilities. To determine the effect of storage environment, pods of four cultivars were stored in four environments and the seeds were subjected to standard germination tests and immediately followed by field emergence evaluations. Cultivar affected both field emergence and germination. Storage environment affected field emergence, and to a lesser extent, germination (P = 0...

Interactive effects of planting date and cultivar on tomato spotted wilt of peanut.

Field experiments were conducted at Gainesville and Marianna, FL in 2004 and 2005 in which severity of spotted wilt, caused by Tomato spotted wilt virus, and pod yield were compared in six peanut (Arachis hypogaea) cultivars. The six cultivars included the moderately field resistant cultivars ANorden, C-99R, and Georgia Green; the highly field resistant cultivars AP-3 and DP-1; and the susceptible cultivar SunOleic 97R. There were four trials at each location, with four planting dates that ranged from late March to early June. Tomato spotted wilt severity in moderately resistant and susceptible cultivars was lower at Gainesville than at Marianna in both years in moderately resistant and susceptible cultivars. Trends in incidence for the two locations were less evident for AP-3 and DP-1. At Gainesville, there were few differences in tomato spotted wilt severity, and severity ratings were similar for Georgia Green and SunOleic 97R in two of four trials in 2004 and across all trials in 2005. At Marianna, severity ratings were lower for Georgia Green than for SunOleic 97R in six of the eight trials, and severity of tomato spotted wilt was lower for AP-3, C-99R, and DP-1 than for Georgia Green in all eight trials. In 2004, there was a trend toward decreasing severity ratings for Georgia Green and SunOleic 97R with later planting dates, but not for AP-3 or DP-1 at Marianna. Split-plot field experiments were also conducted at Tifton, GA in 2005 through 2007 in which incidence of tomato spotted wilt and pod yield were compared for peanut cultivars AP-3 and Georgia Green across planting dates ranging from late April through late May. Incidence of tomato spotted wilt was lower for AP-3 than for Georgia Green within each planting date of all years, and planting date effects were smaller in AP-3, if observed at all, than in Georgia Green. In most planting dates of all three trials, yields were higher for AP-3 than for Georgia Green. The relationships between yield and planting date were not consistent. These results indicate that the level of field resistance in AP-3 and DP-1 cultivars is sufficient to allow planting in late April without greatly increasing the risk of losses to tomato spotted wilt.

Field Evaluation of Virginia-Type Peanut Cultivars for Resistance to Tomato Spotted Wilt Virus, Late Leaf Spot, and Stem Rot

Abstract Susceptibility to viral and fungal diseases is a major factor limiting profit in the production of virginia-type peanuts (Arachis hypogaea L.) in the South Carolina coastal plain. Field te...

Target enrichment sequencing in cultivated peanut ( Arachis hypogaea L.) using probes designed from transcript sequences

Enabled by the next generation sequencing, target enrichment sequencing (TES) is a powerful method to enrich genomic regions of interest and to identify sequence variations. The objective of this study was to explore the feasibility of probe design from transcript sequences for TES application in calling sequence variants in peanut, an important allotetraploid crop with a large genome size. In this study, we applied an in-solution hybridization method to enrich DNA sequences of seven peanut genotypes. Our results showed that it is feasible to apply TES with probes designed from transcript sequences in polyploid peanut. Using a set of 31,123 probes, a total of 5131 and 7521 genes were targeted in peanut A and B genomes, respectively. For each genotype used in this study, the probe target capture regions were efficiently covered with high depth. The average on-target rate of sequencing reads was 42.47%, with a significant amount of off-target reads coming from genomic regions homologous to target regions. In this study, when given predefined genomic regions of interest and the same amount of sequencing data, TES provided the highest coverage of target regions when compared to whole genome sequencing, RNA sequencing, and genotyping by sequencing. Single nucleotide polymorphism (SNP) calling and subsequent validation revealed a high validation rate (85.71%) of homozygous SNPs, providing valuable markers for peanut genotyping. This study demonstrated the success of applying TES for SNP identification in peanut, which shall provide valuable suggestions for TES application in other non-model species without a genome reference available.

Phenotyping and genotyping parents of sixteen recombinant inbred peanut populations

ABSTRACT In peanut (Arachis hypogaea L.), most agronomically important traits such as yield, disease resistance, and pod and kernel characteristics are quantitatively inherited. Phenotypic selectio...

Consideration of peg strength and disease severity in the decision to harvest peanut in southeastern USA

ABSTRACT The indeterminate nature and underground fruiting habit of peanut (Arachis hypogaea L.) makes it a challenge to determine the optimal harvest time. The objectives of this study were (1) to gain additional information about how maturity and canopy health influence peg strength, yield, and grade and (2) to address anecdotal claims of differences in peg strength and digging losses among cultivars. Field trials were established in Citra, FL, and Tifton, GA. Two peanut cultivars (“Georgia-06G” and “Tifguard”) were grown under two fungicide programs (full program: every 14-day spraying interval; and reduced program: every 28-day spraying interval), and harvested at three different maturity levels (early, optimum, and late based on an accumulated growing degree day method). The fungicide program had a significant impact on yield only in 2013 at Citra, likely because the canopy structure was decreased because of fungal disease known as leaf spots (causal agents: Cercospora arachidicola and Cercosporidium personatum). The timing of the harvest had a significant impact on yield, grade, peg strength, and digging loss. In addition, yield, grade, peg strength, and digging losses differed between the peanut cultivars. These results show that reduced fungicide program might affect the yield because of the disease severity and that the optimal harvest time should consider the level of the defoliation. Although there was no correlation between peg strength and digging loss, over-maturity can cause more digging losses compared to optimal harvest time. Tifguard had higher digging loss than Georiga-06G. This study provides additional useful information on cultivars to growers.