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© 2006 Plant Management Network. Response of Peanut Cultivars to Seeding Density and Row Patterns B. L. Tillman and D. W. Gorbet, North Florida Research and Education Center, University of Florida, Marianna 32446; A. K. Culbreath and J. W. Todd, Coastal Plain Experiment Station, The University of Georgia, Tifton 31793 Corresponding author: Barry Tillman. btillman@ifas.ufl.edu Tillman, B. L., Gorbet, D. W., Culbreath, A. K., and Todd, J. W. 2006. Response of peanut cultivars to seeding density and row patterns. Online. Crop Management doi:10.1094/CM-2006-0711-01-RS. Abstract Spotted wilt, caused by Tomato spotted wilt virus (genus Tospovirus; family Bunyaviridae) is a major disease of peanut (Arachis hypogaea L.) in the southeastern United States. Research has shown that several management factors such as increased plant stands (seeding density) and twin-row planting pattern can help minimize losses from spotted wilt; however, the single most important factor is cultivar resistance. New cultivars with excellent spotted wilt resistance have been developed, and studies were conducted in Marianna, FL during 2001-2004 to evaluate their response to seeding density and twin-row vs. single-row planting patterns. Pod yields were greater and spotted wilt severity was lower in twin-row compared to single-row planting patterns, but there was no cultivar × row-pattern interaction. All cultivars, regardless of their level of resistance to spotted wilt benefit from being planted in twin-rows. No differences in yield or spotted wilt severity were noted among seeding density treatments of 5, 6, and 7 seed per linear foot in 2001-2004. However, in 2004, yield was reduced and spotted wilt increased at 4 compared to 5, 6, or 7 seeds per linear foot. These results indicate that twin-row planting patterns and seeding densities of 5 to 7 seeds per linear foot benefit peanut cultivars with at least intermediate resistance to spotted wilt. Spotted Wilt of Peanut Spotted wilt, caused by Tomato spotted wilt tospovirus is widespread on peanut (Arachis hypogaea L.) in the production regions of the southeastern United States including Alabama, Florida, and Georgia (7). The disease can cause severe yield reductions resulting in large monetary losses for farmers. In 1997 in Georgia alone, spotted wilt caused an estimated $40 million in losses on peanuts (3). Researchers have developed strategies to help farmers reduce losses from the disease. Production practices such as increased plant stands (seeding density) (8,10), twin-row planting pattern (1,2), delaying planting until May, use of phorate insecticide, and strip tillage can help minimize losses from spotted wilt (7,9). Researchers have noted that increasing the number of plants per acre dilutes the thrips vector such that there is a lower probability of individual plant infection (6). The mechanism by which twin-row planting pattern reduced spotted wilt severity is not clearly understood, but some have theorized that the increased rate of ground coverage in twin rows as compared to single rows may affect the ability of thrips to locate the host (6). The most important factor to minimize losses from spotted wilt is cultivar resistance (7). The University of Georgia Tomato Spotted Wilt Risk Index integrates these factors to help farmers develop a strategy for minimizing the risk of losses from spotted wilt (5). In the Southeast, ‘Georgia Green’ has replaced ‘Florunner’ as the most widely planted cultivar, largely due to its resistance to spotted wilt and the extreme susceptibility of Florunner. Additionally, twin-row planting patterns, reduced tillage methods, and delayed planting have become increasingly popular. New cultivars with better spotted wilt resistance than Georgia Green have been developed, but many of these new cultivars have not been tested under the production practices recommended for reducing spotted wilt losses. These studies were conducted to evaluate the performance of new spotted-wilt-resistant cultivars as affected by planting pattern and seeding densities. Field Studies Studies were conducted in 2001-2004 at the North Florida Research and Education Center near Marianna, Florida. The soil type is a Chipola loamy sand, and all tests were grown with overhead irrigation as needed to maintain adequate soil moisture. Over the four-year period, ten cultivars with varying levels of resistance to spotted wilt were evaluated (Table 1). Prior to planting each season, seed were evaluated for germination and only seed lots with at least 85% germination were used for planting. Experiments were planted on 24-25 April 2001, 2-3 May 2002, 24 and 28 April 2003, and 21-22 April 2004. Table 1. Historical values for relative maturity and Spotted Wilt Virus Risk Indexy and average spotted wilt ratings from row pattern studies and seeding density studies conducted in Marianna, Florida 2001-2004.
x Maturity: E = early (125-130 days after planting-DAP), M = medium (133-139 DAP), and L = late (145-150 DAP). y Based on the 2005 University of Georgia Disease Risk Index, a tool developed to help peanut farmers minimize the risks of losses from TSWV. Point values represent the relative susceptibility of genotypes based on disease incidence and pod yield under disease pressure. Lower numbers mean greater resistance. z Based on the 2003 University of Georgia Tomato Spotted Wilt Risk Index. Density experiments. The experimental design for the seeding density tests was a randomized complete block with a factorial treatment arrangement of peanut cultivars and seeding densities. In 2001-2003, seeding densities were 5, 6, and 7 seeds per linear foot of row and in 2004 they were 4, 5, 6, and 7 seeds per linear foot. The rows were spaced 36 inches apart, so this corresponds to 58080, 72600, 87120, and 101640 seeds/acre (23504, 29380, 35256, and 41132 seeds/hectare). The number of genotypes varied depending on the year. Planting pattern experiments. The experimental design for the planting pattern test was a randomized complete block with a split-plot treatment arrangement. Cultivars were assigned to main plots and row-patterns were assigned to the sub-plots. Plots consisted of two rows (or two pairs of rows) in all years, and were 20 feet long in 2001-2003 and 15 feet long in 2004. Rows in the single-row plots were 36 inches apart. The twin-row pattern consisted of four rows in the row-spacing configuration of 9 inches (twin rows), 18 inches (gap), and then 9 inches (twin rows), with a 36-inch gap on the outside of each twin row. Thus, for each twin-row plot, there were 18 inches between the inner rows, 9 inches between the twin rows, and 36 inches between the outer rows. The seeding density in the row pattern studies was 6 seeds per linear foot in each row in the single-row treatment and 3 seeds per linear foot in each row in the twin-row treatment such that each plot had the same number of planted seeds per unit area. The overall density of each plot was 87,120 seeds/acre for both the single- and twin-row treatments. Data collected included pod yields, spotted wilt rating (1-10, where 1 = no disease and 10 = all plants severely diseased), percentage total sound mature kernels (all whole kernels riding a 16/64-inch screen plus all sound splits), and the weight of 100 seeds. Data analysis. Data were analyzed using the MIXED Procedure of SAS considering replication, year and all interactions with replication and year random effects (SAS Institute Inc., Cary, NC). Differences in treatment means were evaluated using the LSMEANS statement with the PDIFF option. Analyses were conducted for each year, and across years using cultivars common to the three-year period 2002-2004 and to the four-year period 2001-2004. Treatment effects and means were considered different if the probability of a greater F-value was less than 0.05. In addition to analysis of variance, a simple linear regression of pod yield on spotted wilt ratings was performed. Cultivar Effects on Spotted Wilt In general, spotted wilt ratings from these studies rank the cultivars similarly to the University of Georgia Tomato Spotted Wilt Index point rankings (Table 1). Only ratings of the cultivars Carver and MDR 98 seemed to differ from the index rankings. In the case of MDR98, it was grown in 2001 and 2002, but spotted wilt in 2001 was very mild. In the case of Carver, spotted wilt ratings varied from year to year. In two of the three years in which spotted wilt was moderate to severe (2002 and 2004) and in 2001, spotted wilt ratings in Carver were similar to those in Georgia Green, but in 2003, spotted wilt was less severe in Carver than in Georgia Green. Row Pattern Effects on Pod Yield and Spotted Wilt Ratings Pod yields and spotted wilt ratings were affected by row pattern and cultivar each year of the study, and in the combined three- and four-year datasets (Table 2). Pod yields were consistently higher in twin rows vs. single rows by 400 to 600 lb/acre when averaged over cultivars, but yield differences within a single cultivar were less consistent (Fig. 1). Ratings for spotted wilt severity were consistently lower in twin rows vs. single rows when averaged over cultivars (Fig. 2). There was no consistent effect of row pattern on the percentage of total sound mature kernels or the hundred-seed weight (Table 2). The inconsistency of total sound mature kernel response to twin-row culture has been noted before. Baldwin et al. (1) found higher TSMK in twin vs. single rows among four cultivars, but later found no differences in total sound mature kernels between row patterns with two cultivars (2). There was no consistent row pattern × cultivar interaction for any trait measured indicating that all cultivars respond similarly to row pattern.
Table 2. Significance of F-Values from analysis of variance comparing peanut cultivars and row patterns in Marianna, Florida.
*,** = significant to at least the 0.05 and 0.001 probability levels, respectively. ns = not significant. x Three cultivars, Georgia Green, Carver, and Hull. y Six cultivars, Andru II, ANorden, C-99R, Carver, Georgia Green, and Hull. Seeding Density Effects Seeding densities of 5, 6, or 7 seed per foot of row did not affect pod yield, spotted wilt, total sound mature kernels, or the weight of 100 seeds. However, in 2004 when seeding densities were 4 to 7 seeds per foot of row, pod yield and spotted wilt ratings varied with seeding densities. A minimum of 85% stand establishment was observed in our density plots. Pod yields from the 4 seed per foot treatment were 320 (P > t = 0.075), 530 (P > t = 0.006), and 309 (P > t = 0.096) lb/acre lower than those from the 5, 6, or 7 seed per foot treatments respectively. Likewise, spotted wilt ratings were greater in the 4 seed per foot treatment by 0.5 (P > t = 0.076), 0.9 (P > t = 0.002), and 0.7 (P > t = 0.014) units compared to the 5, 6, or 7 seed per foot treatments, respectively. Gorbet and Shokes (8) found that spotted wilt incidence decreased as plant density within rows increased. In that study, spotted wilt incidence was lowest when plants were 3 inches apart. In the present study, the lowest seeding density of 4 seed per foot would result in an average of approximately 3½ inches between plants (assuming 85% seed to plant survival), but spotted wilt incidence was higher in that treatment in 2004 compared to 5, 6, or 7 seed per foot. This suggests that the critical plant density to minimize spotted wilt incidence is less than 3 inches between plants (more than 4 plants per foot of row) which is similar to the findings of Branch et al. (4). They found that spotted wilt incidence was lowest at 23 seed per meter of row (about 7 seed per foot of row) and greatest at 10 seed per meter of row (about 3 seed per foot of row). Cultivar Resistance The relationship between pod yields and spotted wilt ratings shows that for each single-digit increase in the spotted wilt rating on our 1-10 scale, pod yield was reduced by about 623 lb/acre on average (Fig. 3). This demonstrates the value of cultivar resistance in combating spotted wilt of peanut. For example, the most resistant cultivars such as ‘AP-3’ and ‘DP-1’ had average ratings of less than 3, whereas cultivars such as ‘Georgia Green’ and ‘AndruII’ had ratings of 5 or more (Table 2). Given the relationship between pod yield and spotted wilt ratings, spotted wilt could cause over 1200 lb/acre in pod yield loss in cultivars that differ by 2 points on the 1-10 scale.
Conclusions and Recommendations Cultivar, row pattern, and seeding density are important factors in managing spotted wilt. Genetic resistance is the most critical factor of all. Our data indicate that cultivars with more resistance to spotted wilt than Georgia Green may still benefit from twin-row culture and seeding densities of at least 5 seed per foot of row (72,600 seed per acre in 36 inch rows), even though that benefit may not be entirely associated with a reduction in spotted wilt severity. For example, the spotted wilt rating of ‘Hull’ was 1.3 points less (on the 1-10 scale) in twin vs. single rows and it had significantly greater pod yield in twin rows. However, spotted wilt ratings for ‘Carver’ were not different in twin vs. single rows, but the pod yield was greater in twin rows. Additionally, there was no cultivar × row pattern interaction for pod yield indicating that pod yield of resistant and susceptible cultivars increased in twin-row culture. In comparison to more susceptible cultivars, those with very strong spotted wilt resistance could perform well under somewhat lower seeding density and/or in single-row culture, but will likely benefit from twin-row culture. Literature Cited 1. Baldwin, J. A., Beasley, J. P., Brown, S. L., Todd, J. W., and Culbreath, A. K. 1998. Yield, grade, and tomato spotted wilt incidence of four peanut cultivars in response to twin vs. single row planting patterns. Proc. Am. Peanut Res. Ed. Soc. 30:51. Abstr. 2. Baldwin, J. A., McDaniel, R., McGriff, D. E., and Tankersley, B. 2001 Yield, grade and tomato spotted wilt incidence of Georgia Green and AT201 peanut when planted in twin vs. single row pattern. Proc. Am. Peanut Res. Ed. Soc. 33:31. Abstr. 3. Bertrand, P., ed. 1998. 1997 Georgia Plant Disease Loss Estimates. Univ. Ga. Coop. Ext. Publ. Pathol. 98-107. 4. Branch, W. D., Baldwin, J. A., and Culbreath, A. K. 2004. Peanut genotype × seeding rate interaction among TSWV-Resistant, runner-type peanut cultivars. Peanut Sci. 30:108-111. 5. Brown, S. L., Todd, J. W., Culbreath, A. K., Baldwin, J. A., and Beasley, J. P., Kemerait, B., and Pappu, H. 2003. Minimizing spotted wilt of peanut. Univ. Ga. Ext. Bull. 1165. 6. Brown, S. L., Culbreath, A. K., Todd, J. W., Gorbet, D. W., Baldwin, J. A., and Beasley, J. P., Jr. 2005. Development of a method of risk assessment to facilitate integrated management of spotted wilt of peanut. Plant Dis. 89:348-356. 7. Culbreath, A. K., Todd, J. W., and Brown, S. L. 2003. Epidemiology and management of tomato spotted wilt in peanut. Ann. Rev. Phytopathol. 41:53-75. 8. Gorbet, D. W., and Shokes, F. M. 1994. Plant spacing and tomato spotted wilt virus. Proc. Am. Peanut Res. Ed. Soc. 26:50. Abstr. 9. Todd, J. W., Culbreath, A. K, Brown, S. L., Gorbet, D. W., Shokes, F. M., Pappu, J. A., Baldwin, J. A., and Beasley, J. P. 1998. Development and validation of and integrated management system for spotted wilt disease in peanut. Proc. Am. Peanut Res. Ed. Soc. 30:51. Abstr. 10. Wehtje, G., Weeks, R., West, M., Wells, L, and P., Pace. 1994. Influence of planter type and seeding rate on yield and disease incidence in peanut. Peanut Sci. 21:16-19. |
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