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© 2013 Plant Management Network.
Accepted for publication 8 June 2013. Published 12 August 2013.


Spotted Wilt Disease Evaluation Among High-Oleic Peanut Cultivars


W. D. Branch, Department of Crop and Soil Sciences, and A. K. Culbreath, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, 2360 Rainwater Road, Tifton, GA 31793-5766


Corresponding author: W. D. Branch. wdbranch@uga.edu


Branch, W. D., and Culbreath, A. K. 2013. Spotted wilt disease evaluation among high-oleic peanut cultivars. Online. Plant Health Progress doi:10.1094/PHP-2013-0812-01-RS.


Abstract

The release of high-oleic, United States runner and virginia market type peanut (Arachis hypogaea L.) cultivars has been steadily increasing during the past several years. Two planting dates were utilized for disease evaluation and agronomic performance among these newer high-oleic cultivars. The first planting date test was in mid-April to allow for increased incidence of spotted wilt disease caused by Tomato spotted wilt virus (TSWV). The second planting date test was in mid-May to allow for less TSWV and provide more of an optimum time by comparison. Significant differences (P ≤ 0.05) were found within each of the three (3-year) averages among cultivars for TSWV and total disease (TD) incidence, pod yield, and dollar values. Among the virginia-types, Georgia Hi-O/L, Georgia-05E, and Georgia-08V, and runner-types, Georgia-02C and Georgia-09B, consistently had the lowest TSWV and TD incidence and the highest pod yield and dollar values in both the mid-April and mid-May planting date tests. No significant differences were found between the mid-April and the mid-May planting dates when averaged across this 5-year study for TSWV and TD incidence, pod yield, and dollar values. This suggests that the high-level of TSWV-resistance among these newer high-oleic cultivars should have a greater influence than planting dates on agronomic performance.


Introduction

High-oleic peanut (Arachis hypogaea L.) genotypes were first reported by Norden et al. (21) in the Florida breeding program. Two closely related experimental peanut lines (F435-2--1 and F435-2--2) had oleic (C18:1) fatty acid of 79.91% and 79.71%, respectively which were significantly higher than all other genotypes tested. Likewise, the linoleic (C18:2) fatty acid of these same two lines were significantly lower than other genotypes at 2.14% and 2.29%, respectively.

On the average in Georgia, the normal oleic fatty acid methyl ester (FAME) percentage of runner-type peanut cultivars is approximately 52%, and the linoleic FAME percentage is about 29% (8). Consequently, high-oleic peanut cultivars offer a major improvement in oil quality and extended shelf-life of peanut and peanut products compared to the normal peanut oil chemistry.

Unfortunately, many of the first high-oleic peanut cultivars, ‘SunOleic 95R’ (15), ‘SunOleic 97R’ (16), and ‘Flavor Runner 458’ are highly susceptible to spotted wilt disease caused by Tomato spotted wilt virus (TSWV) in the southeast US (7,10,14). So, the objective of this 5-year study was to evaluate for disease resistance and agronomic performance of the more recently released high-oleic cultivars utilizing two planting dates in Georgia. The first planting date was in mid-April to allow for increased incidence of TSWV and the second planting date was in mid-May to allow for less TSWV and provide a more optimum time for comparison (9).


Effect of Disease on Performance of High-Oleic Cultivars

During five consecutive years (2005-2009), several different high-oleic runner and virginia-type peanut cultivars were evaluated each year in two planting-date tests. Field tests were conducted at the University of Georgia, Coastal Plain Experiment Station, Tifton Campus utilizing these two planting dates, early-planted tests (mid-April) and optimum-planted tests (mid-May). Early-planting dates were 21 April 2005, 19 April 2006, 23 April 2007, 16 April 2008, and 17 April 2009; whereas the optimum-planting dates were 16 May 2005, 18 May 2006, 14 May 2007, 14 May 2008, and 15 May 2009.

A randomized complete block design was used in each test with five replications. Seeding rates were six seeds per 30.5 cm of row. Plots consisted of two rows 6.10 m long × 1.83 m wide (0.81 m within and 1.02 m between rows on adjacent plots). Georgia Cooperative Extension Service recommended cultural practices with irrigation were used throughout each growing season. These field trials were in a three-year rotation following cotton (Gossypium sp. L.) and corn (Zea mays L.). Individual entries were dug near optimum maturity based upon hull-scrape method (26) as determined from adjoining border rows of each test.

Disease assessment. Incidence of TSWV was first assessed at approximately 70 d after planting, when TSWV is usually the only disease occurring at this time during the growing season. General yellowing and wilting are symptoms of tomato spotted wilt that typically occur late in the season (12). These symptoms are not always accompanied by other more diagnostic symptoms of the disease, and are often very similar to symptoms of white mold or stem rot caused by Sclerotium rolfsii Sacc. Therefore, percentages of total disease which were scored prior to digging, included primarily TSWV and any soilborne disease. A disease hit equaled one or more symptomatic plants within a 30.5-cm section of row (22).

Pod yields. After digging and threshing, pods were dried with forced warm air to 6% moisture. Pod samples were then hand-cleaned over a screen table before weighing for yield determinations. Market grades were determined according to federal state inspection service procedure for runner and virginia-type peanuts, respectively (25). Gross dollar values were calculated from yield and grade based upon USDA-Farm Service Agency (FSA) peanut loan schedule for each crop year.

Statistical analysis. Data from each three-year set of common cultivars were subjected to analysis of variances. Waller-Duncan’s T-test (k-ratio = 100) were used for multiple cultivar mean separation of significant differences at P ≤ 0.05. Years were considered as random factors in the combined analyses. Overall mean data from each test was subjected to analysis of variance, and least significant differences (LSD) were used for planting date mean separation at P ≤ 0.05.


Disease and Cultivar Effects

Three (3-year) average effects were used to evaluate a common set of high-oleic peanut cultivars for disease resistance and agronomic performance. Each of these 3-year averages included both early-planted and optimum-planted test results. Significant differences (P ≤ 0.05) were found for TSWV incidence, total disease incidence, pod yield, and dollar value among the high-oleic runner and virginia-type cultivars in each of the 3-year averages.


Table 1. Three-year average effect of TSWV and total disease incidence on pod yield and dollar value among seven runner-type and four virginia-type, high-oleic, peanut cultivars planted in mid-April and mid-May, 2005-2007.


During 2005-2007 (Table 1), average TSWV incidence in the mid-April and mid-May planting was lowest among ‘Georgia-09B’ (6), ‘Georgia-02C’ (3), ‘Georgia-05E’ (4), and ‘Georgia Hi-O/L’ (2) and was highest among ‘Brantley’ (19) and ‘Tamrun OL02’ (23). Similar results were also found for average total disease incidence. Highest pod yield and dollar values were found among the virginia-types, Georgia Hi-O/L, Georgia-05E, and ‘Georgia-08V’ (5) and the runner-types, Georgia-02C and Georgia-09B.

During 2006-2008 (Table 2), average TSWV incidence was lowest among Georgia-09B, ‘AT-3085RO’, Georgia-02C, Georgia Hi-O/L, ‘Florida-07’ (17) and Georgia-05E, and highest TSWV incidence was found with Brantley in both the mid-April and mid-May planting tests. Total disease incidence was found to be similar to the TSWV incidence. However, highest pod yields were found with virginia-types, Georgia Hi-O/L and Georgia-08V and with the runner-types, Georgia-02C and Georgia-09B. The highest dollar values were found with the two virginia-types, Georgia Hi-O/L and Georgia-05E. However, Georgia-05E was not significantly different in dollar value from Georgia-02C, Georgia-09B, and Georgia-08V.


Table 2. Three-year average effect of TSWV and total disease incidence on pod yield and dollar value among five runner-type and four virginia-type, high-oleic, peanut cultivars planted in mid-April and mid-May, 2006-2008.


During 2007-2009 (Table 3), average TSWV incidence was lowest among Georgia-09B, Georgia-02C, AT-3085RO, Georgia Hi-O/L, and ‘York’ (18) and was highest with the virginia-type cultivar Brantley. Average total disease incidence was lowest with the runner-types, York and Georgia-09B, and was highest with virginia-type cultivar, Brantley. Pod yield and dollar values were highest with the virginia-type cultivar, Georgia Hi-O/L and the runner-type cultivar, Georgia-09B. However, Georgia Hi-O/L and Georgia-09B were not significantly different from Georgia-08V and Florida-07 in pod yield, and Georgia-09B was not different from Georgia-02C, Georgia-08V, and Georgia-05E in dollar value.


Table 3. Three-year average effect of TSWV and total disease incidence on pod yield and dollar value among seven runner-type and five virginia-type, high-oleic, peanut cultivars planted in mid-April and mid-May, 2007-2009.


Implications for Disease Management of High-Oleic Cultivars

Spotted wilt disease. Unexpectedly, no significant differences (P ≤ 0.05) were found between the mid-April and mid-May planting date tests when averaged across the 5-years in this study for TSWV and total disease incidence, pod yield, and dollar values (Table 4). Also, no significant differences (P ≤ 0.05) were found among years when averaged across the two planting dates for total disease incidence, pod yield, and dollar values. However, there was a significant difference found among years for TSWV (Fig. 1). It is interesting to note that 2005 had the most TSWV which agrees with previously reported disease loss estimates in Georgia for TSWV (11,20).


Table 4. Five-year average effect of TSWV and total disease incidence on pod yield and dollar value among two planting dates of high-oleic, peanut cultivars, 2005-2009.


 

Fig. 1. Yearly effect of Tomato spotted wilt virus (TSWV) incidence averaged across high-oleic cultivars for two different planting dates: (  ) = mid-April and ( – – ) = mid-May in Georgia.

 

Tillman et al. (24) had found that mid-May planting dates in Florida produced the highest pod yield average across all genotypes compared to either late April or early June planting dates. However, TSWV ratings and pod yield varied among peanut genotypes, but often the TSWV ratings were similar in May and June planting dates. Culbreath et al. (13) also found that the relationship between yield and planting date were inconsistent among genotypes, and the effects of planting date on TSWV were not reflected in pod yield.

In summary, the high level of TSWV resistance among these newer high-oleic cultivars should have a greater influence than planting date on agronomic performance as was found in this present 5-year study. The improved TSWV resistance (or higher levels of resistance) found in these cultivars may also allow more flexibility with other cultural practices used for suppression of spotted wilt disease.

High-oleic cultivars. Georgia Hi-O/L was among the first high-oleic peanut cultivars released with appreciable field resistance to TSWV (7,14). In earlier studies, Culbreath et al. (14), reported final incidence of TSWV in Georgia Hi-O/L (tested as GA 94007) similar to or lower than that of the moderately resistant cultivar, ‘Georgia Green’ (1). Similarly, Branch et al. (7) reported that Georgia Hi-O/L had much lower incidence of TSWV and much higher yield than the high-oleic cultivars Flavor Runner 458 and SunOleic 97R, and that incidence of TSWV and yield were similar to that of Georgia Green. Since then, several other cultivars have been released with the high-oleic oil chemistry.

Results from this study shows that among the runner-type cultivars, Georgia-02C and Georgia-09B, were found to have consistently among the lowest TSWV and total disease incidence and the highest pod yield and dollar values in both the mid-April and mid-May planting date tests. Although less consistent across experiments, cultivars York and Florida-07 also had disease ratings that were among the lowest in some trials. Among the virginia-types, Georgia Hi-O/L, Georgia-05E, and Georgia-08V, were found to have consistently the lowest TSWV and total disease incidence and the highest pod yield and dollar values in both planting date tests.

In the southeastern US, utilization of the desirable high-oleic fatty acid oil chemistry was severely impeded by the high level of susceptibility to TSWV in the earlier cultivars released with that trait. However, several more recently released cultivars, including both runner and virginia market types, with high-oleic oil chemistry evaluated in this study have sufficient field TSWV resistance to allow production with minimal impact from spotted wilt disease.


Literature Cited

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