Although rhizoma peanut has potential to provide high quality forage during the summer when forage nutritive value is typically low,it requires 2 to 3 yr for complete coverage (Rice et al., 1996; Williams et al., 1997). Another weakness associated with rhizoma peanut is the high cost of planting along with the long grazing-deferment period during establishment (Rice et al., 1995). Defoliation during the year after establishment greatly reduces rhizome production (Saldivar et al., 1992); therefore, utilization should be deferred until stands are completely established. Rhizoma peanut is typically only recommended for sandy soils with a pH ranging from 5.8 to 6.5 (Prine et al., 1990; French and Prine, 2006). However, Reed and Ocumpaugh (1991) identified 23 genotypes tolerant to Fe deficiency chlorosis on high pH calcareous soils from a screening of 69 PIs. Of these 23 genotypes, two (PI 262819 and PI 262821), originally from Paraguay (French et al., 1993), were identified as having agronomic potential with greater height, spread, and estimated DM production (Butler et al., 2006).
Rhizoma peanut releases are currently limited to the extreme southern United States due to poor winter hardiness (French and Prine, 2006). Initial winter conditions and harvest management during the second season after establishment can greatly affect rhizoma peanut survival (Butler et al., 2006). Identifying germplasm that establishes more rapidly, tolerates cold temperatures, and is adapted to a wider range of soils than the currently available genotypes might expand the growing area of rhizoma peanut. Therefore, the objective of this study was to evaluate rhizoma peanut genotypes for better establishment characteristics and cold tolerance on various soils.
Materials and methods
During the 2006 to 2010 seasons, a randomized complete block design experiment evaluating 16 rhizoma peanut genotypes was initiated at Tifton, GA (2006, 2007, and 2008, Pelham loamy sand, Loamy-siliceous-thermic Arenic Paleaquults), Gene Autry, OK (2006, Dale silt loam, Fine-silty, mixed, superactive, thermic Pachic Haplustoll), Burneyville, OK (2007, Eufaula loamy sand, Siliceous, thermic Psammentic Paleustalfs; 2008, Ashport clay loam, Fine-silty, mixed, superactive, thermic Fluventic Haplustolls), and Vashti, TX (2007, Anocon loam soil, Fine, mixed, thermic Udic Paleustalfs; 2008, Bonti fine sandy loam, Fine, mixed, active, thermic Ultic Paleustalfs). Genotypes evaluated included A6 (PI 210555), A10 (PI unknown), A20 (PI 162801), A23 (PI 118457), A27 (PI unknown), A42 (PI unknown), A44 (PI 231318), A76 (PI unknown), A156(PI unknown), A160 (PI unknown), HL335 (PI 338317), and HL410 (PI 338280) (all experimental lines from the USDA-ARS); TX62 (PI 262819) and ‘Latitude 34’ (Muir et al., 2010) recently released for northern Texas, and two cultivars from Florida (Arbrook and Florigraze; Prine et al., 1986, 1990).
Soil pH values ranged from 4.7 to 8.3 (Table 1). Within each site, individual 15-cm rhizomes were planted in the greenhouse in late winter (February) and then transplanted to the field in April (after the last killing frost). Sites were fertilized one time with P and K according to soil test recommendation before planting. Each plot consisted of five plants spaced 61-cm apart, which resulted in an effective 1.5 by 3 m plot, with 1.5 m alleys between each entry. In each year, two replications per location were used due to limited amount of rhizomes available. During the initial establishment year at each location, the number of shoots that emerged, the length of rhizoma peanut spread, and plant height was recorded for each plant on a monthly interval throughout the growing season (April–October); however, only the measurements taken in October, the end of the season, are reported. Dry matter yield was not estimated during the first season due to higher probability of winter kill (Butler et al., 2006). Weeds were controlled as needed depending on species present: 2,4-DB (Butyrac) 4-(2,4-dichlorophenoxy) butyric acid (Albaugh , Inc. / Agri-Star, Ankeny, IA) was applied at 0.84 kg a.i. ha−1 to control broadleaf weeds, clethodim (Select) (±)-2-[(E)-1-[(E)-3-chloroallyloxyimino]propyl]-5-[2-(ethylthio)propyl]-3- hydroxycyclohex-2-enone (Winfield Solutions, LLC, St. Paul, MN) applied at 0.28 kg a.i. ha−1 was used to control grass weeds, and imazapic (Plateau) 5-methyl-2-(4-methyl-5-oxo-4-propan-2-yl-1H-imidazol-2-yl)pyridine-3-carboxylic acid (BASF Specialty Products, Research Triangle Park, NC) applied at 0.067 kg a.i. ha−1 was used for residual control of grasses, broadleaves, and sedges. In addition, plots were maintained weed-free by hand weeding throughout the season.
|Gene Autry, OK||2006||Dale silt loam||6.8||276||632|
|Tifton, GA||2006||Pelham loamy sand||5.2||25||103|
|Burneyville, OK||2007||Eufaula loamy sand||7.9||99||256|
|Vashti, TX||2007||Anocon loam||6.4||99||576|
|Burneyville, OK||2008||Ashport clay loam||8.3||41||793|
|Vashti, TX||2008||Bonti fine sandy loam||4.7||13||233|
During the second season, DM yield and percent ground coverage were estimated once in July, while in the third season, DM yields and percent coverage were estimated in both July and October. Total yield is reported in the third season as the sum of July and October yields. Yields were estimated at the northern locations by clipping the entire plot with a forage harvester (Hege, Colwich, KS) to approximately 2.5-cm height. Dry matter yield at Tifton, GA, was not included, since there was no winter damage or loss of stands at this location. Forage samples were weighed at harvest and dried in a forced draft oven set at 50°C to a constant weight for 3 to 4 d. Dry matter yield was determined from the percent DM and plot yields.
All data were analyzed as mixed models, with replication, year, and location as random effects and rhizoma peanut genotype as fixed effect, using the PROC MIXED procedure of SAS (SAS Institute, 1999). Significance was determined at the p < 0.05 level. The PDIFF feature of the LSMEANS procedure was used to compare means. Coverage data were subjected to arcsine transformation before statistical analysis and back-transformed for data presentation.
Results and discussion
Precipitation varied across years and locations but was generally less than the 30-yr average (Table 2). At Gene Autry, OK, precipitation ranged from 15 to 60% less than average and at Vashti, TX, precipitation ranged from 15 to 34% less than average. At the Burneyville, OK, location, precipitation ranged from 28% less than average in 2008 to greater than 60% above average in 2009. At Tifton, GA, precipitation ranged from 45% below average in 2006 to 39% above average in 2009. The absolute low temperature recorded the winter after establishment was similar across the Oklahoma and Texas locations, ranging from –12 to –10°C in 2006 to 2008 seasons. In the winter of 2009–2010, temperatures were slightly colder, reaching –16 to –14°C. However, temperatures at Tifton, GA, were considerably milder with low temperatures reaching –7 to –5°C.
|Gene Autry, OK||737||305||533||432||635|
|Low temperature† (°C)|
|Gene Autry, OK||–||–11||–10||–12||–14|
|No. days minimum temperature below 0°C|
|Gene Autry, OK||–||47||59||61||69|
|No. days max temperature below 0°C|
|Gene Autry, OK||–||9||0||5||5|
Percent Coverage at the End of the Establishment Year
Averaged across years and locations, percent coverage at the end of the establishment year (7 mo after planting) ranged from 9 to 74% (Table 3). Others have reported similar variation (5 to 100%) for percent coverage of Florigraze and Arbrook 8 mo after planting in Florida, depending on year and location (Williams, 1993; Williams et al., 1997). Greater coverage ratings indicates quicker establishment, which is important to reduce competition from weeds and could result in more rapid utilization (Butler et al., 2006). Genotype A6 (PI 210555) had the greatest coverage (74%), followed by genotypes A156 and A160 (51 and 56%, respectively), while genotypes A10 and A42 had lesser coverage (9 and 13%, respectively) than all genotypes except A27 and A76. The remaining genotypes were intermediate and generally did not differ from the released cultivars Florigraze, Arbrook, and Latitude 34, which had 25, 25, and 30% coverage, respectively.
|Entry||PI identifier||Lateral spread†||Coverage||Shoot|
|A6||210555||111 cd‡||74 e||117 e|
|A10||–||59 a||9 a||6 a|
|A20||162801||92 c||29 c||30 bc|
|A23||118457||99 c||28 c||36 bc|
|A27||–||90 bc||23 abc||47 cd|
|A42||–||95 c||13 a||36 bc|
|A44||231318||99 c||32 c||35 bc|
|A76||–||73 ab||16 ab||21 ab|
|A156||–||106 c||51 d||59 d|
|A160||–||99 c||56 d||65 d|
|Arbrook||–||73 ab||25 bc||28 bc|
|Florigraze||–||70 a||25 bc||23 ab|
|HL335||338317||106 c||27 c||34 bc|
|HL410||338280||121 d||36 c||34 bc|
|Latitude 34||–||91 c||30 c||31 bc|
|TX62||262819||92 c||25 bc||33 bc|
Lateral Spread at the End of the Establishment Year
The average distance that an individual plant spread laterally at the end of the establishment year ranged from 59 to 121 cm (Table 3). This parameter gives an indication of how far the rhizomes spread during the establishment year, which could be useful in determining the population density needed for successful establishment. Genotypes that spread farther could compensate for lower densities or could establish more quickly. Genotypes HL410 (PI 338280) and A6 (PI 210555) tended to have the greatest spread, while genotypes A10 and Florigraze had lesser spread than all genotypes except A76 and Arbrook. The remaining genotypes were intermediate and similar to the released cultivar Latitude 34 (91 cm). Butler et al. (2006) reported that Arbrook and Florigraze spread from 142 to 191 cm when planted using similar methodology; however, their report was for 14 mo after planting, instead of 7 mo in this study.
Number of Shoots at the End of the Establishment Year
The number or density of shoots ranged from 6 to 117 shoots plant−1 when planted on 61-cm intervals (Table 3). Genotypes with increased density establish more quickly and may have greater rhizome mass that improves winter survival. Genotype A6 (PI 210555) had the greatest average shoot count per plant (117), followed by genotypes A156 and A160 (59 and 65 shoots plant−1, respectively). Genotype A10 had lesser shoot density than all genotypes except A76 and Florigraze, with only six shoots per plant. The remaining genotypes were intermediate and similar to Arbrook and Latitude 34 (28 and 31 shoots plant−1, respectively). It is difficult to compare results to other published data due to differences in establishment methods, but Butler et al. (2006) reported total shoot counts ranging from 119 to 380 shoots m−2 and Williams (1993) reported 2 to 65 shoots m−2 depending on year and establishment method.
Combining all three parameters for establishment, genotype A6 (PI 210555) was superior to all other genotypes followed by genotype A156 and A160. Therefore, these genotypes have better establishment characteristics and should be better adapted to compete with weeds and may have better winter survival due to increased rhizome growth.
Lateral Spread in the Second Season
Distance of lateral spread per plant in July of the second season after planting ranged from 52 to 182 cm for all genotypes (Table 4). These results are similar to those reported elsewhere. For example, Butler et al. (2006) reported that Arbrook, Florigraze, and Latitude 34 spread ranged from 140 to 198 cm 14 mo after planting in south Texas. Genotype A20 (PI 162801) exhibited less lateral spread than all genotypes except A27, A76, Florigraze, and HL335 (PI 338317). Genotypes A6 (PI 210555), A23 (PI 118457), A42, A44 (PI 231318), A156, A160, HL410 (PI 338280), Arbrook, and Latitude 34 had the greatest spread and did not differ from each other.
|July of second season after planting
||Third season after planting|
|Entry||PI identifier||Spread diameter||Coverage||Yield||Total yield|
|cm||%||kg DM ha−1|
|A6||210555||134 cde†||43 defg||510 d||2160 c|
|A10||–||107 bcd||16 abcd||0 a||550 ab|
|A20||162801||52 a||4 a||2 a||80 a|
|A23||118457||145 de||39 cdef||150 ab||1400 bc|
|A27||–||68 ab||15 abc||0 a||100 ab|
|A42||–||149 de||24 bcdef||100 ab||1340 abc|
|A44||231318||182 e||45 efg||190 abcd||900 ab|
|A76||–||101 abcd||16 abcd||490 cd||1290 abc|
|A156||–||120 bcde||46 fg||470 cd||2610 cd|
|A160||–||122 bcde||86 h||1360 e||2260 cd|
|Arbrook||–||109 bcde||29 bcdef||370 bcd||1680 bc|
|Florigraze||–||70 ab||10 ab||40 ab||30 a|
|HL335||338317||89 abc||21 bcde||240 abcd||330 ab|
|HL410||338280||130 cde||34 cdef||370 bcd||560 ab|
|Latitude 34||–||155 de||69 gh||1000 e||3630 d|
|TX62||262819||107 bcd||27 bcdef||170 abc||320 ab|
Percent Ground Coverage in the Second Season
Percent ground coverage ranged from 4 to 86% in July of the second season after planting (Table 4), which was generally similar to the values reported at the end of the first season, except for genotypes A160 and Latitude 34, for which coverage was approximately 1.5 and twofold greater than the first season, respectively. This indicates that these two genotypes may be better adapted and may have superior winter survival compared to other entries.
Dry Matter Yield in the Second Season
Dry matter yield ranged from 0 to 1360 kg ha−1 (Table 4) in July of the second season after planting, which is substantially lower than values reported by others in warmer latitudes (Butler et al., 2006, 2007; Terrill et al., 1996), illustrating the winter loss at these northern locations. Genotypes Latitude 34 and A160 yielded 1000 and 1360 kg DM ha−1, respectively, which was greater than the yields of all other genotypes. Therefore, these two genotypes may have greater cold tolerance since they recovered more quickly and produced more DM compared to other genotypes at these northern locations.
Total Dry Matter Yield in the Third Season
Distance of lateral spread and coverage exhibited similar trends among genotypes as the data reported for end of establishment year and second season after planting. These data are not shown in an attempt to reduce the presentation of redundant data. Rhizoma peanut genotypes were harvested twice (July and October), and both harvests were summed and reported as total DM yield. Total DM yield ranged from 30 to 3630 kg ha−1 (Table 4), which is considerably lower than total DM yields reported by Butler et al. (2006, 2007) and Terrill et al. (1996) at more southern latitudes, most likely a result of significant winter kill at these northern locations. In the third season after establishment, Latitude 34 produced greater total DM yield (3630 kg ha−1) than all genotypes except A156 and A160 (2610 and 2260 kg DM ha−1, respectively). Florigraze was among the lesser yielding genotypes, producing only 30 kg DM ha−1 for the entire growing season. Therefore, genotypes A160 and Latitude 34 consistently had the greatest coverage and DM production and may have greater cold tolerance, which would allow for greater utilization of rhizoma peanut.
Winter survival as indicated by DM yield and percent ground coverage the seasons following the establishment year varied by genotype. Low temperatures during these years ranged from –12 to –10°C at the Oklahoma and Texas locations. Latitude 34 and genotype A160 appear to be slightly more winter hardy than the other genotypes in the study. However, following the 2009–2010 winter season when temperatures ranged from –16 to –14°C, none of the rhizoma peanuts survived at the southern Oklahoma or north Texas locations regardless of location, soil type, or establishment year (data not shown). Ball et al. (2002) reported that Florigraze rhizoma peanut survived temperatures as low as –9°C, while Terrill et al. (1996) found that Florigraze survived –12°C temperatures at Fort Valley, GA (32° N 83° W). However, Butler et al. (2006) reported that newly established Latitude 34 survived sustained freezing temperatures as low as –14°C in December 2005 at Stephenville, TX (32° N, 98° W), and Ardmore, OK (34° N, 97° W). The winter of 2009–2010 was unique in that these locations received two greater-than-254-mm snow events and above-normal winter precipitation compared to the below-average precipitation the previous years. Therefore, the increased soil moisture in combination with temperatures below –12°C could have limited rhizoma peanut production and adaptation. Andrews (1987) describes several ways in which low temperature stress may contribute to plant death, including cell membrane disorganization during freezing exposure, dessication stress, anaerobic stress due to restriction of gas exchange by flooding and ice encasement, soil heaving, and low-temperature diseases. Further research is needed to determine the physiological effects of freezing temperatures on rhizoma peanut in these cool environments.
Although rhizoma peanut genotypes were slow to establish in this study, two genotypes (A156 and A160) exhibited greater establishment (coverage and spread) than current commercial cultivars. Rhizoma peanuts were also low yielding at the northern locations, but genotypes A160 and Latitude 34 consistently produced the greatest DM yield across locations, which suggests these two genotypes may have greater cold tolerance than traditional commercial cultivars Florigraze and Arbrook. Utilizing new genotypes adapted to colder climates could slightly expand the current area of rhizoma peanut adaption. However, there are definite northern limitations to the adaptation of even A160 and Latitude 34 since these did not survive in the final year of the study. There are, therefore, risks to recommending or growing rhizoma peanut much beyond the current region of where it is presently grown until better genotypes are identified.