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Agronomy Dep., North Florida Research and Education Center, Institute of Food and Agricultural Sciences, Univ. of Florida, 3925 Hwy. 71, Marianna, FL 32446
* Corresponding author (btillman{at}ufl.edu).
ABSTRACT
‘AP-4’ (Reg. No. CV-106, PI 654070) peanut (Arachis hypogaea L. subsp. hypogaea var. hypogaea) cultivar was developed by the University of Florida, Florida Agricultural Experiment Station, North Florida Research and Education Center (NFREC) near Marianna, FL. Tested under the experimental designation UF03325, AP-4 was approved for release in 2007. AP-4 was developed from a cross made in 1996 between a University of Florida breeding line (88 x OL3-HO6-) and the F1 (‘Andru 93’ x F435-HO). Lines were advanced using single seed descent in the F2 to F4 generations and pedigree selection in the F5 and F6 generations. Seed from three F7 plants were bulked to form the line later designated UF03325. AP-4 has larger-than-average runner-type seeds and pods. The average weight of 100 sound mature kernels of AP-4 was 71 g compared with 57 g for ‘Georgia Green’ (P < 0.0001), a typical runner-type cultivar. The prostrate growth habit of AP-4 is typical of runner-type peanut cultivars. Release of AP-4 was based on its pod yield and seed grade (total sound mature kernels [TSMK]). In 19 tests in Florida over 3 yr, the TSMK of AP-4 averaged 77% compared with 73% for ‘AP-3’ (P < 0.0001). AP-3 is most noted for its high level of resistance to spotted wilt caused by Tomato spotted wilt tospovirus, but low TSMK has restricted its acceptance among farmers. AP-4 has competitive pod yield potential and good resistance to spotted wilt. The improved TSMK of AP-4 should provide improved revenue compared to AP-3.
Abbreviations: NFREC, North Florida Research and Education Center • PSREU, Plant Science Research and Education Unit • TSMK, total sound mature kernels • TSWV, Tomato spotted wilt virus • UPPT, Uniform Peanut Performance Tests • WFREC, West Florida Research and Education Center
‘AP-4’ (Reg. No. CV-106, PI 654070) peanut (Arachis hypogaea L. subsp. hypogaea var. hypogaea) cultivar was developed by the University of Florida, Florida Agricultural Experiment Station, North Florida Research and Education Center (NFREC) near Marianna, FL. Tested under the experimental designation UF03325, AP-4 was approved for release in 2007.
AP-4 is a product of the long-term peanut breeding program of the University of Florida, Institute of Food and Agricultural Sciences. A history of the program was given by Gorbet (1999). The primary goal of the program is to develop peanut cultivars with improvements in the major characteristics that affect continued profitability and sustainability of peanut growers in the southeastern United States and the peanut industry. Traits of primary importance are pod yield and total sound mature kernel (TSMK) percentage. Peanuts are sold on a tonnage basis with premiums or discounts that are determined by the TSMK percentage and other grade factors. In 2008, the national posted price of one metric ton of peanuts (pods with seeds) was $391.19. Each percentage point of TSMK in a metric ton of peanuts was valued at $5.338. As an example of other grade factors, there is a $3.75 deduction per metric ton if the grading process identifies 2% damaged kernels. Similarly, there is a deduction of $0.88 per metric ton for every percentage point of "sound splits" (kernels that split in half during the shelling process) above 4%. The USDA Farm Service Agency publishes these annual regulations governing the value of peanuts on its Website (http://www.fsa.usda.gov/FSA/webapp?area=home&subject=prsu&topic=col-nl-pp).
Several fungal diseases and one viral disease afflict peanut in the southeastern United States. Because these diseases reduce pod yield and TSMK percentage, breeding for disease resistance is also an important part of the program. Although AP-4 was not developed with the aim of producing a cultivar with high levels of resistance to the fungal leaf spot diseases caused by Cercospora arachidicola Hori and Cercosporidium personatum (Burk. & M.A. Curtis) Deighton or white mold caused by Sclerotium rolfsii Sacc., all cultivars grown in the southeastern United States must have an acceptable level of resistance to spotted wilt caused by Tomato spotted wilt virus (TSWV: genus Tospovirus; family Bunyaviridae) (Culbreath et al., 2003). Excellent fungicides are available to control these fungal diseases, but cultivar resistance is the foundation of managing spotted wilt in peanut (Brown et al., 2008).
The cultivar Georgia Green (Branch, 1996) has been widely planted throughout the southeastern United States for the past 10 yr. Although there are no clear-cut categories of resistance, Georgia Green can be classified as having a moderate level of resistance to spotted wilt, with a score of 30 for spotted wilt on the Peanut Disease Risk Index (Brown et al., 2008). Therefore, one objective was to develop a cultivar with resistance to spotted wilt that is superior to that of Georgia Green. However, the primary impetus behind release of AP-4 was its competitive pod yield and excellent kernel grade (percentage TSMK) in comparison to ‘AP-3’ (Gorbet, 2007). AP-3 was released in 2003 under exclusive license to Andersons Peanut, Inc., which was later purchased by Birdsong Peanuts, Inc. The low TSMK percentage of AP-3 has limited its production even though its resistance to TSWV is among the best available among current cultivars. In addition to excellent grade and resistance to spotted wilt, release of AP-4 was based on its very competitive pod yield potential.
Methods
Tested experimentally as UF03325, AP-4 originated from a cross made in a greenhouse at the NFREC near Marianna, FL, in 1996. The female parent was a University of Florida breeding line (88 x OL3-HO6-), and the male was the F1 (‘Andru 93’ x F435-HO). The female parent was a University of Florida breeding line with medium maturity and normal oleic fatty acid. Andru 93 is an early-maturing normal oleic fatty acid runner type (Gorbet and Knauft, 1995). F435-HO1 is a breeding line that was not released by the University of Florida, Florida Agricultural Experiment Station. The high-oleic trait in peanut was first reported in F435-HO1 by Norden et al. (1987) and results in improvements in the fatty acid profile of peanut oil. Specifically, it increases oleic fatty acid in peanut oil from about 50 to 55% in normal peanuts to about 75 to 80% and decreases linoleic fatty acid from about 20 to 25% in normal peanuts to 2 to 5%. The purpose of the cross was to incorporate the high-oleic oil chemistry into a breeding population that would allow selection for improved pod yield, kernel grade, medium maturity, and resistance to TSWV.
AP-4 was developed through a modified single-seed descent selection program during the F2 to F4 generations at the Plant Science Research and Education Unit. (PSREU) near Gainesville, FL, and pedigree selection was practiced in the F5 and F6 generations at the NFREC near Marianna, FL. All selection generations were grown under standard management including regular fungicide applications to control foliar and soilborne fungal diseases. Single plants were selected during the F5 and F6 generations for pod size and shape and resistance to TSWV. Seed from three F7 plants were bulked together to form the line 96x48–1-Bx3-2-b3, which was entered into yield tests in 2001 in Marianna. The line has been maintained as a bulk since that time and breeds true to type.
In 2003, the line 96x48-1-Bx3-2-b3-B was entered into the Uniform Peanut Performance Tests (UPPT) at the Marianna location as a local option, a line tested in a single UPPT site (Branch et al., 2004). The Florida local options group was also tested near Gainesville at the PSREU. Under the designation UF03325, AP-4 was an official entry in the UPPT in 2004 and 2005 (Branch et al. (2005) and 2006). In the UPPT, UF03325 was tested in 9 locations in 2004 and 10 locations in 2005. It was also tested in five different experiments at the NFREC in 2004. In 2005, UF03325 was an entry in six tests at the NFREC. In 2006, UF03325 was entered in one test grown at the NFREC, the West Florida Research and Education Center (WFREC), and the PSREU and four other tests at the NFREC. In 2007, UF03325 was entered in two tests grown at the NFREC, WFREC, and PSREU and five tests grown at NFREC and PSREU.
In all Florida tests beginning in 2003, plots consisted of two 6.1-m-long rows spaced 91 cm apart. In-furrow insecticides were not applied at the NFREC, but either aldicarb or phorate was applied at the WFREC and the PSREU. The seeding density was 19.7 seeds m–1. Cultural practices used in tests in Florida were common to all years and included overhead irrigation (NFREC and PSREU, whereas WFREC tests were rain-fed), conventional tillage with moldboard plowing in the spring, standard recommendations for weed and insect control as well as a full-season fungicide program, which stipulates fungicide applications every 10 to 14 d to control foliar diseases such as leaf spots and soilborne diseases such as white mold.
In tests designed to evaluate white mold resistance, no fungicides with activity against S. rolfsii were used, and the plots were inoculated with S. rolfsii. noculum of S. rolfsii was grown on sterilized whole oat groats and diluted before application with oat (Avena sativa L.) and/or corn (Zea mays L.). On the day before applying the inoculum and for 3 d subsequent, fields were watered with 0.6 to 1.2 cm from overhead irrigation each day. White mold tests were conducted similarly to those described by Gorbet et al. (2004).
Quality data were collected from field plot samples to estimate grade factors and oil chemistry during 2003 to 2007. In Florida, fatty acid composition was determined with a Hewlett-Packard 5890A gas chromatograph (Agilent Technologies Inc., Santa Clara, CA) following procedures described by Metcalf et al. (1966) and Zeile et al. (1993) and using a ThermoNicolet 630 FT-IR instrument (Thermo Fisher Scientific Inc., Waltham, MA) as described by Tillman et al. (2006). Flavor evaluations are not presented but were conducted by the USDA–ARS Market Quality and Handling Research Unit in Raleigh, NC, as part of the UPPT (see http://www.ars.usda.gov/main/site_main.htm?modecode=66-45-05-00). Although not reported here, grade and physical attributes of the pods and seeds were also measured by the USDA–ARS National Peanut Research Laboratory in Dawson, GA, as part of the UPPT (http://www.ars.usda.gov/Services/docs.htm?docid=12479). In Florida, grading was conducted by University of Florida staff using Federal–State Inspection Service farmer stock grading equipment and standard procedures. The weight of the grade samples was 200 g, and all debris and immature pods were removed from the sample before grading.
Paired comparisons were generated using AGROBASE Generation II, Varietal Comparisons Module (Agronomix Software, Inc., Winnipeg Manitoba Canada, http://www.agronomix.mb.ca/gen2.html) to compare AP-4 to Georgia Green, ‘Georgia-03L’ (Branch, 2004), and AP-3.
Characteristics
Plants of AP-4 have a prostrate growth habit typical of runner cultivars. Its foliage is medium green (Munsell Book of Color 2.5G 5/9), and it has a semiprominent main stem. The testa of AP-4 seeds is tan in color. AP-4 requires approximately 135 d after planting to mature under irrigation in Florida and is considered to have medium relative maturity, which is adapted to most growing regions in the southeastern United States.
The seed weight of AP-4 is in the upper range of the typical runner market type. The average weight of 100 seed exceeds that of Georgia Green and AP-3 but is similar to Georgia-03L, another large-seeded runner type (Table 1 ). The USDA definition for a runner market type requires that the proportion of virginia pods be less than 40% (Knauft et al., 1987). This clearly categorizes AP-4 as a runner-type since it averaged 13 to 18.5% virginia pods in tests in Florida (Table 1). However, the peanut industry also evaluates overall seed size and prefers runner cultivars with seed size in the range of 55 to 65 g per 100 seed. Large seed have implications for the proportion of various grade sizes. Compared with the typical runner-type cultivar Georgia Green, AP-4 has fewer medium and more jumbo kernels (Table 1). Although the average seed weight of AP-4 is greater than that of AP-3, AP-4 has more medium kernels and fewer jumbo kernels than AP-3. This is because measurement of medium and jumbo kernels is one-dimensional and AP-4 seeds are slightly longer and narrower than seeds of AP-3. The extra length of AP-4 accounts for its heavier seed compared with AP-3. The jumbo and medium seed profile of AP-4 is similar to that of Georgia-03L. However, Georgia-03L has more virginia pods than does AP-4.
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In the 2004 UPPT, AP-4 ranked fourth in pod yield (5230 kg ha–1) in a combined analysis of ten tests over nine locations and was not statistically lower than the highest yielding entry, GA 011557 (Table 10 in Branch et al., 2005). GA 011557 was later released as ‘Georgia-06G’ (Branch, 2007a). The TSMK percentage of AP-4 in that same analysis was 76.4%, which was not different than the best entry in the test. In the combined analysis of the three southeastern UPPT sites in Alabama, Georgia, and Florida, AP-4 ranked fourth in pod yield (5449 kg ha–1) and was not different from the highest yielding entry (Table 11 in Branch et al., 2005). The TSMK percentage of AP-4 was 75.3% and was not statistically lower than the entry with the highest TSMK percentage (76.9%).
In the overall 2005 UPPT analysis (Table 11 in Branch et al., 2006), AP-4 ranked fourth in pod yield, which was less than the highest-yielding entry, UF04327 (released as ‘Florida-07’, Gorbet and Tillman, 2009) but similar to the pod yield of GA 011514 (released as ‘Georgia-07W’, Branch and Brenneman, 2008) and GA011568 (released as ‘Georgia Greener’; Branch, 2007b). The TSMK of AP-4 was among the highest in the test (72.5%) and was not different (P < 0.05) than GA 011568, which had highest TSMK percentage (74.1%). Results were similar in the combined analysis of the three southeastern locations in Alabama, Georgia, and Florida (Table 13 in Branch et al., 2006). Pod yield of AP-4 ranked fourth and was not different (P < 0.05) than the highest-yielding entry. The TSMK percentage of AP-4 was 68.8% and not less than the entry with the highest TSMK percentage.
Availability
Application for U.S. Plant Variety Protection for AP-4 has been filed and is pending. If approved, AP-4 can be produced only as a class of certified seed. Inquiries concerning foundation seed and production of AP-4 should be directed to the Florida Foundation Seed Producers, Inc., P.O. Box 309, Greenwood, FL 32443. Breeder seed will be maintained by the Florida Agricultural Experiment Station. Seed has been submitted to the National Plant Germplasm System for distribution after the expiration of the PVP certificate. Small seed samples for research purposes are available from the authors.
Conclusions
In southeastern United States in 2007, Georgia Green occupied about 50% of the runner-type acreage and Georgia-03L and AP-3 occupied about 10% each in 2008. AP-4 offers improvements in TSMK percentage compared to AP-3 and resistance to spotted wilt compared with Georgia Green and Georgia-03L.
Footnotes
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication November 21, 2008.
References
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