Introduction

In Georgia, the most recent disease loss and cost of control estimates for peanut (Arachis hypogaea L.) was $214.5 million which represents 31.6% of the 2020 total crop value (Kemerait, 2023). This was an increase compared to 2015 where total damage and cost of control was $153.0 million which represented 22.3% of the peanut crop value (Kemerait, 2017). During both years (2015 and 2020), white mold (WM) or stem rot caused by Agroathelia rolfsii (Curzi) C. C. Tu & Kimbr, = Sclerotium rolfsii Sacc. resulted in the highest percent reduction in total crop value compared to other diseases at 6.0% and 8.0%, respectively. However these other soilborne and foliar peanut diseases also cause considerable economical damage, resulting in several additional millions of U. S. dollars lost due to damage and cost of control each year (Kemerait, 2017; Kemerait, 2023).

In addition to the soilborne disease white mold, tomato spotted wilt caused by Tomato spotted wilt virus (TSWV), early leaf spot caused by Passalora arachidicola (Hori) U. Braun syn. Cercospora arachidicola (Hori), and late leaf spot caused by Nothopassalora personata (Berk & M. A. Curtis) U. Braun, C. Nakesh., Videira & Crous syn. Cercospordium personatum (Berk. & Curt.) Deighton are foliar diseases that are endemic each year and cause considerable yield loss. Dryland peanut production in Georgia accounts for roughly half of the total hectarage during any given growing season (Monfort, 2022). Consequently, the objective of this study was to assess these multiple diseases and the performance of several different peanut genotypes without fungicides or insecticides under dryland test conditions for disease resistance and drought tolerance.

Materials and Methods

During five-years (2018-22), several peanut genotypes were assessed for multiple diseases [TSWV, white mold (WM), total disease (TD) = TSWV+WM, (early and late) leaf spot]. Within each year, these runner and virginia-type genotypes were evaluated for dryland field performance at the Gibbs Research Farm (latitude: 31.43°N and longitude: 83.59°W) near the University of Georgia, Coastal Plain Experiment Station, Tifton, GA.

A randomized complete block field design with four replications was used each year. No fungicides, insecticides, or irrigation were applied. These dryland field tests were conducted on a Tifton loamy sand soil type (fine-loamy, siliceous, thermic Plinthic Kandidult). All plots in each test consisted of two rows, 6.1m long x 1.8 m wide, and six seed were planted per 30.5 cm of row. Early April planting dates were used to increase TSWV and WM disease pressure (Tillman et al., 2007 and Culbreath et al., 2009). These field tests were also in a desirable three-year rotation following corn (Zea mays L.) and cotton (Gossypium sp.)

TSWV incidence (0-100%) was first assessed at midseason (approximately 70 days after planting), when TSWV is usually the predominant disease present and easier to assess. Additionally, percentages of total disease (TD) incidence were assessed prior to digging, which included primarily TSWV but also any soilborne disease. A disease “hit” equaled one or more symptomatic diseased plants in a 30.5-cm section of row (Rodriguez-Kabana et al., 1975). Leaf spot ratings among all genotypes were recorded on an individual plot basis within a few days prior to digging during each growing season. Both early and late leaf spot were prevalent and evaluated together on a 0-9 visual canopy rating scale where 0 = no visible leaf spot (immune) and 9 = dead and defoliated plants (very highly susceptible). The 0-9 leaf spot rating scale used in this study is most similar to the 1-9 scale of Pittman (1995), except for the addition of the 0 = immune rating. Immediately after digging and inverting, the incidence of only WM was also assessed among the different genotypes. This is the most definitive white mold rating assessment since signs and symptoms of this disease are often below ground, especially under dryland production. For TSWV, TD, and WM assessments, the disease incidence was determined by counting the number of hits in both rows and converting to a percentage of total row length for each plot.

Each genotype was individually dug near optimum maturity based upon the hull-scrape method from adjacent border plants (Williams and Drexler, 1981). After harvesting with a two-row combine, peanut pods from each plot were dried with forced warm-air to approximately 6% seed moisture content. Pod samples were then cleaned before weighing for yield determinations. Grade samples were presized and shelled on federal state inspection service (FSIS) equipment accordingly for runner and virginia-type peanut, respectively (USDA-AMS, 2019). Gross dollar values were calculated from yield and grade based upon USDA – Farm Service Agency (FSA) peanut loan schedules for each year. Dollar values included premiums for % ELK in virginia-types, and deductions included visual damage > 1% and sound splits > 4% for both market types as specified in annual peanut loan schedules. (USDA-FSA, 2024).

Data from each test and combined data across tests were statistically analyzed by analysis of variance (ANOVA) using general linear model PROC GLM in SAS 9.4 version (SAS Institute, Inc. Cary, NC). Waller-Duncan Bayesian T-test (k-ratio = 100) was used for mean separation of significant differences (P≤0.05).

Results

Rainfall during the five growing seasons recorded at each test site showed that the seven-month totals for three seasons (2019, 2020, and 2022) out of the five years were below the long-term average at Tifton, GA (Table 1). Likewise, four average monthly (April, July, September, and October) rainfall out of the seven during the five growing seasons was also below the long-term average. Even during the two high rainfall seasons (2018 and 2021), there were at least one or more months where drought stress was a major limiting factor. Maximum and minimum air temperatures averaged across the April thru October growing season (Table 2) showed that 2019 had the highest temperatures (31.6 and 19.4 °C), whereas 2021 had the lowest seven-month maximum and minimum temperatures (29.3 and 18.2 °C), respectively. Compared to the long-term (1923-2016) averages, the air temperatures were similar for the maximum temperatures for each month as well as the seven-month average. However, there seems to be a consistent trend in the seven-month minimum air temperature being slightly higher for each month and averaged 1.1 °C higher across the growing season (Table 2).

Table 1

Five-year average monthly rainfall distribution during the growing season at Tifton, GA, 2018-22.

Table 2

Five-year average monthly maximum and minimum air temperature (°C) distribution during the growing season at Tifton, GA, 2018-22.^a

Significant differences (P≤0.05) were found among both runner and virginia genotypes within each year (Tables 3-7) and across years (Table 8) for multiple diseases and overall field performance (pod yield and dollar values). Except for 2018 and 2021, significant differences were found for TSWV among the many assessed peanut genotypes. However during 2018 (Table 3), TD incidence which included predominantly TSWV near harvest time did show that the runner-type cultivar ‘Georgia-12Y’ (Branch, 2013) had the lowest percent TD of all genotypes, but it was not significantly lower than GA 122706; GA 132705; ‘Georgia-20VHO’ (Branch, 2021); ‘Georgia-18RU’ (Branch, 2019); ‘Georgia-13M’ (Branch, 2014); GA 132712; and one virginia-type cultivar, ‘Georgia-19HP’ (Branch and Brenneman, 2020). Likewise in 2018, the advanced Georgia breeding line, GA 132705 had the lowest leaf spot rating, but it was not significantly different from GA 132712, (a sister line); GA 152545; Georgia-12Y; ‘TifNV-High O/L’ (Holbrook et al., 2017) and the virginia-type cultivars Georgia-19HP, ‘Georgia-11J’ (Branch, 2012), and ‘Bailey II’. The virginia-type cultivars ‘Sullivan’ and Bailey II had numerically lowest WM disease incidence, but they were not significantly different from three other virginia-types and 14 runner-types. These multiple disease assessments agree with a previous report (Chapin et al., 2010) regarding TSWV, WM, and leaf spot resistance for the virginia-type cultivar ‘Bailey’ (Isleib et al., 2011) the recurrent parent of Bailey II. Pod yield and dollar values were the highest for the Georgia breeding line, GA 152545. However, it was not significantly higher than several other runner-types for both pod yield and dollar values.

Table 3

Disease assessment and dryland field performance among runner and virginia-type peanut genotypes when planted early and grown without fungicides or insecticides and no-irrigation at Tifton, GA, 2018

During 2019 (Table 4), Georgia-12Y had the lowest percent incidence of TSWV, but it was not significantly lower than several other runner and virginia-types. Likewise in 2019, ‘AU-NPL 17’ had the lowest percent incidence of TD, but it also was not significantly lower than several other genotypes. Whereas, leaf spot rating was the lowest for Sullivan, but it was not significantly different from the virginia-types: Bailey II, Georgia-19HP, Bailey and runner-types: AU-NPL 17 and ‘Tifguard’ (Holbrook et al., 2008). Percent WM was the lowest for Bailey II, but it was not significantly lower than all of the other virginia-types and several of the runner-types. Pod yield and dollar values were both the highest for Georgia-12Y. However, it was not significantly different from ‘Georgia-07W’ (Branch and Brenneman, 2008) and TUFRunner ‘511’ in pod yield, and Georgia-07W, ‘TUFRunner 511’ (Tillman and Gorbet, 2017), GA 142510, GA 132712, and GA 163119 for dollar value.

Table 4

Disease assessment and dryland field performance among runner and virginia-type peanut genotypes when planted early and grown without fungicides or insecticides and no-irrigation at Tifton, GA, 2019

In 2020 (Table 5), no data was collected for the percentage of white mold (WM) due to COVID-19 pandemic restrictions. However, Georgia-12Y and ‘Georgia-06G’ (Branch, 2007) were found to have the lowest percentage of TSWV. But these two runner-type cultivars were not significantly different from several other runner-types at mid-season. Near harvest, the lowest TD percentages were found in Georgia-12Y. However, it was not significantly different from several other runner and virginia-types. Georgia-19HP had the lowest leaf spot rating of all genotypes, but it was not significantly different from several other runner and virginia-types. Pod yield and dollar values were the highest for ‘TifJumbo’ and Georgia-12Y, respectively. However, both high performing cultivars were not significantly different from each other and several other different genotypes.

Table 5

Disease assessment and dryland field performance among runner and virginia-type peanut genotypes when planted early and grown without fungicides or insecticides and no-irrigation at Tifton, GA, 2020

As previously mentioned, no significant differences were found among the runner and virginia genotypes for TSWV incidence during 2021 (Table 6). However, significant differences were found for TD incidence. ‘Georgia-22MPR’ (Branch and Brenneman, 2023) had the lowest percentage of TD among these genotypes, but it was not significantly different from several other runner and virginia-types. For leaf spot, four virginia cultivars, ‘Sullivan’, Bailey, Bailey II, and ‘Wynne’ had the lowest significant ratings of all genotypes. These same four virginia cultivars also had the lowest WM percentages, however all four were not significantly different from many other runner and virginia-types. Field performance again resulted in Georgia-12Y having the highest pod yield and dollar values similar to 2019 and 2020. However, it was not significantly different from several other runner and virginia-types.

Table 6

Disease assessment and dryland field performance among runner and virginia-type peanut genotypes when planted early and grown without fungicides or insecticides and no-irrigation at Tifton, GA, 2021

During 2022 (Table 7), percent TSWV incidence was the lowest with GA 192710 and Georgia-22MPR; whereas, the highest TSWV percentages were found with FloRun ‘T61’ and FloRun ‘331’ (Tillman, 2021). However, these genotypes were not significantly different from several other runner and virginia-types. In addition, TD was the lowest with Georgia-12Y and the highest with FloRun ‘331’. In contrast, Georgia-12Y was not significantly different for TD from several genotypes; whereas, FloRun ‘331’ was significantly different from all genotypes, except GA 192517 for TD. Leaf spot pressure was low during 2022. Most genotypes had less than a 3.0 rating, except for GA 182521 and GA 192517 which had the highest leaf spot ratings of 3.2 and 3.0, respectively. GA 192517 was not significantly different from Georgia-16HO and Georgia-22MPR in leaf spot rating. TUFRunner ‘297’ (Tillman, 2018) had the highest percentage of WM; whereas, Georgia-12Y had the lowest WM percentage. Both were not significantly different from many other runner and virginia genotypes. Georgia-16HO had the highest pod yield and dollar value, except it was not significantly higher than Georgia-21GR. Both of these runner-type cultivars were higher than all other runner and virginia-types, except that Georgia-21GR was not significantly better than GA 192710 for pod yield and dollar value.

Table 7

Disease assessment and dryland field performance among runner and virginia-type peanut genotypes when planted early and grown without fungicides or insecticides and no-irrigation at Tifton, GA, 2022.

Table 8

Five-year average disease assessment and dryland field performance among 14 runner and five virginia-type peanut cultivars when planted early and grown without fungicides or insecticides and no-irrigation at Tifton, GA, 2018-22.

Discussion

In the five-year combined results for multiple disease and dryland performance (Table 8), Georgia-12Y had the lowest TSWV percentage (resistance), but it was not significantly different from Georgia-06G, ‘Georgia-14N’ (Branch and Brenneman, 2015), Georgia-20VHO, and Georgia-19HP. Likewise, Georgia-12Y was found to have the most resistance for late-season TD. However, it was not significantly different from Georgia-06G. These results agree with another recent report (Branch, et al., 2021b).

In the leaf spot disease assessment, Bailey II and Sulllivan were found to be the most leaf spot resistant, but both virginia-type cultivars were not significantly different from Wynne, Georgia-19HP, and TifNV High O/L. These results agree with previous findings that early April plantings have less leaf spot pressure than later planting dates (Branch, et al., 2021a).

WM disease assessments found that Bailey II, Sullivan, Wynne, TifNV High O/L, FloRun ‘331’, Georgia-12Y, Georgia-14N, Georgia-07W, AU-NPL17, and Georgia-19HP were the most resistant under these dryland conditions with good crop rotation which resulted in low overall WM disease incidence. However, under heavier WM disease pressure with irrigation and following continuous peanut rotation, Georgia-12Y has been found to have long-term (>10 years) stable combined general field resistance to both TSWV and WM disease (Branch et al., 2023).

Quizenberry (1982) defined drought tolerance as, “the ability of one genotype to be more productive with a given amount of soil moisture than another genotype”. Overall field performance in this five-year study found that Georgia-12Y had the highest pod yield and dollar value per hectare (drought tolerance). However, it was not significantly higher than Georgia-16HO and Georgia-07W for pod yield and including Georgia-20VHO for dollar value. These results agree in part with a previous report involving minimum-inputs and without irrigation (Branch and Fletcher, 2017). The previous report only included a few of the runner and virginia-type cultivars used in this study.

Coefficient of variation (CV) percentages were relatively higher for these multiple disease assessments across years compared to the pod yield and dollar values (Table 8). These findings suggest greater stability for cultivar field performance (pod yield and dollar values) under these dryland test conditions. Obviously, irrigation provides for more uniform disease pressure versus sporadic rainfall during any given growing season. This was particularly apparent with WM which had the highest CV at 55.6%. Leaf spot disease also had a relatively low mean rating of only 2.7 on a 0-9 scale because of planting early without irrigation (Branch et al., 2021a). In this study, significant differences were found among peanut genotypes for pod yield, dollar values, and several of our most common diseases when grown without fungicides, insecticides, and irrigation. However, drought stress was probably the major overall limiting factor in field performance compared to these low rating diseases.

Literature Cited

Branch W. D. 2007. Registration of ‘Georgia-06G’ peanut. J. Plant Reg. 1: 120.

Branch W. D. 2012. Registration of ‘Georgia-11J’ peanut. J. Plant Reg. 6: 281-283.

Branch W. D. 2013. Registration of ‘Georgia-12Y’ peanut. J. Plant Reg. 7: 151-153.

Branch W. D. 2014. Registration of ‘Georgia-13M’ peanut. J. Plant Reg. 8: 253-256.

Branch W. D. 2019. Registration of ‘Georgia-18RU’ peanut. J. Plant Reg. 13: 326-329.

Branch W. D. 2021. Registration of ‘Georgia-20VHO’ peanut. J. Plant Reg. 15: 290-293.

Branch W. D. and Brenneman T. B., 2008. Registration of ‘Georgia-07W’ peanut. J. Plant Reg. 2: 88-91.

Branch W. D. and Brenneman T. B.. 2015. Registration of ‘Georgia-14N’ peanut. J. Plant Reg. 9: 159-161.

Branch W. D. and Brenneman T. B.. 2020. Registration of ‘Georgia-19HP’ peanut. J. Plant Reg. 14: 306-310.

Branch W. D. and Brenneman T. B.. 2023. Registration of ‘Georgia-22MPR’ peanut. J. Plant Reg. 17: 299-303.

Branch W. D. and Fletcher S. M.. 2017. Combination of disease resistance, drought tolerance, and dollar value among runner and virginia-type peanut cultivars in Georgia. Peanut Sci. 44: 42-46.

Branch W. D., Brown N., and Brenneman T. B.. 2023. Field screening for tomato spotted wilt and white mold (stem rot) resistance among peanut genotypes. Peanut Sci. 50: 1-7.

Branch W. D., Brown I. N., and Culbreath A. K.. 2021a. Planting date effect upon leaf-spot disease and pod yield across years and peanut genotypes. Peanut Sci, 48: 49-53.

Branch W. D., Brown N., Mailhot D. J., and Culbreath A. K.. 2021b. Relative tomato spotted wilt incidence and field performance among peanut cultivars as influenced by different input production practices in Georgia. Peanut Sci. 48:118-122.

Chapin J. W, Thomas J. S., Isleib T. G., Shokes F. M., Branch W. D., and Tillman B. L.. 2010. Field evaluation of virginia-type peanut cultivars for resistance to tomato spotted wilt virus, late leaf spot, and stem rot. Peanut Sci. 37: 63-69.

Culbreath A., Beasley J., Kemerait R., Prostko E., Brenneman T., Smith N., Tubbs S., Paz J., Olatinuro R., Tillman B., Gevens A., Week R., and Hagan A.. 2009. Peanut Rx – The 2009 version of the peanut disease risk index. Pp. 41-56. In: E. P. Prostko (ed.) 2009 Peanut Update. Univ. of Ga. Coop. Ext. Serv. CSS-09-0114.

Holbrook C. C., Timper P., Culbreath A. K., and Kvien C. K.. 2008. Registration of ‘Tifguard’ peanut. J. Plant Reg. 2: 92-94.

Holbrook C. C., Ozias-Akins P., Chu Y., Culbreath A. K., Kvien C. K., and Brenneman T. B.. 2017. Registration of ‘TifNV-High O/L’ peanut, J. Plant Reg. 11: 228-230.

Isleib T. G., Milla-Lewis S. R., Pattee H. E., Copeland S. C., Zuleta M. C., Shaw B. B., Hollowell J. E., Sanders T. H., Dean L. O., Hendrix K. W., Balota M., and Chaplin J. W., 2011. Registration of ‘Bailey’ peanut. J. Plant Reg. 5: 27-39.

Kemerait R. 2017. Peanut p. 13 In: E. L. Little (comp.) 2015 Georgia plant disease loss estimates. Univ. of Ga. Coop. Ext. Serv. Ann. Publ. 102-8.

Kemerait R. 2023. Peanut p. 13 In: E. L. Little (comp.) 2020 Georgia plant disease loss estimates. Univ. of Ga. Coop. Ext. Serv. Ann. Publ. 102-13.

Monfort S. 2022. Chap. 1: Introduction. Pp. 5-7. In: Peanut Production Guide. Univ, of Ga Coop. Ext. No. B1146. Online@ extension.uga.edu/publications.html.

Pittman R. N. (ed). 1995. United States peanut descriptors. USDA, ARS-132. U.S. Govt. Print. Ofc., Washington, D. C.

Quizenberry J. E. 1982. Breeding for drought resistance and plant water use efficiency. Pp. 193-212 In: M. N. Christiansen and C. F. Lewis (eds.). Breeding Plants for Less Flavorable Environments. John Wiley & Sons, New York, NY.

Rodriguez-Kabana R., Backman P. A., and Williams J. C.. 1975. Determination of yield losses to Sclerotium rolfsii in peanut fields. Plant Dis. Rept. 59: 855-858.

Tillman B. L. 2018. Registration of ‘TUFRunner ‘297’ peanut. J. Plant Reg. 12: 31-35.

Tillman B. L. 2021. Registration of ‘FloRun ‘331’ peanut. J. Plant Reg. 15: 294-299.

Tillman B. L. and Gorbet D. W.. 2017. Registration of ‘TUFRunner ‘511’ peanut. J. Plant Reg. 11: 235-239.

Tillman B. L., Gorbet D. W., and Anderson P. C.. 2007. Influence of planting date on yield and spotted wilt of runner market-type peanut. Peanut Sci. 34: 79-84.

USDA-Agricultural Marketing Service. 2019. Farmer’s stock peanuts inspection instructions. U. S. Dept. of Agric, Agric. Mkt. Ser., Specialty Crops Program. Specialty Crop Insp. Div., USDA-AMS, Washington, D. C.

USDA-Farm Service Agency 2024. Commodity loan rates. USDA, Farm Service Agency. https://www.fsa.usda.gov/programs-and-services/price-support/commodity-loan-rates/index.

Williams J. E. and Drexler J. S.. 1981. A non-destructive method for determining peanut pod maturity. Peanut Sci. 8: 134-141.