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Hybrid seed production of pearl millet x napiergrass triploid hybrids.

Interspecific hybrids between pearl millet and napier-grass have high yield potential and excellent forage quality when used for temporary pastures and as cut forage. The primary advantage of PMN hybrids over annual PM in the southeastern USA is to provide improved quality pasture from approximately mid-September to the first killing frost. Winter survival of PMN hybrids occurs in locations receiving only light freezes and the PMN hybrids are long-term perennials in frost-free locations. Vegetative propagation of PMN hybrids is used in the tropics; however, lack of commercial production of [F.sub.1] seed of interspecific hybrids has precluded the use of PMN hybrids in the southeastern USA since the cost of vegetative propagation is considered prohibitive, especially where the hybrids are not perennial. In tropical locations, where long-term production is expected, vegetative propagation is a planting option (Boddorff and Ocumpaugh, 1986; Shank and Chynoweth, 1993).

Burton (1944) first described PMN hybrids and Powell and Burton (1966) suggested a method of commercial seed production using cytoplasmic male sterile (CMS) pearl millet as the seed parent. Napiergrass is short-day sensitive and will not flower before frost in the commercial pearl millet hybrid-producing areas of Texas and Arizona. The purpose of this study was to determine if interspecific hybrid seed could be produced on a commercial scale in a tropical climate and to identify major environmental and production factors affecting production.

Materials and Methods

Plant materials used in this study included three NG clones, Tift N14 (P1337620), Tift N23 (P1365135), and Tift N74 (P1201209), previously determined to be good pollen parents (Hanna and Monson, 1980) and one PM cytoplasmic-nuclear male sterile, Tift 23[A.sub.1][E.sub.1] (Hanna and Burton, 1985). Vegetative stem cuttings (50 cm long) of the three NG clones were randomly planted (to extend pollen shedding period) in June, 1985 in six 60-m-long rows spaced 9 m apart at Kunia. This provided five blocks between NG rows for establishing the PM parent.

The PM received a banded application of 336 kg [ha.sup.-1] of 10-30-10 (N, [P.sub.2][O.sub.5] and [K.sub.2]O), respectively, at planting followed by 23 kg [ha.sup.-1] N banded 30 d after planting. NG received 50 kg [ha.sup.-1] N each year at the time NG was cut back in August or September (except in the 1985 establishment year) with a sickle-bar mower (Table 1). The entire experiment was drip-irrigated. Ant bait (active ingredient, hydramethylnon, tetrahydro-5,5-dimethyl-2(1H)-pyimidinone[3-[4-(trifluoromethyl) phenyl]-1-[2-[4-(trifluoromethyl)phenyl]ethenyl]-2-propenylidene]hydrazone) was applied at 1 kg [ha.sup.-1] when PM was planted to prevent the bigheaded ant [Pheidole megacephala (Fabricius)] from removing the PM seed from the field. The following treatments were used in an attempt to control the spotted munia birds [Lonchura punctulata (Swinhoe)]: 6-mm-mesh polypropylene net, mylar tape, shooting, carbide bird cannons, bird distress calls, chemical treatments, and combinations of these methods. Atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] was applied at 2.4 kg [ha.sup.-1] for control of broadleaf weeds. Tift 23[A.sub.1][E.sub.1] was drilled in rows as indicated in Table 1. A space of 1.5 m was left between the NG row and the adjacent row of PM to allow more sunlight to reach the PM and to reduce competition from NG roots. PMN seed produced on Tift 23[A.sub.1][E.sub.1] was harvested on dates indicated in Table 1. After harvest, NG was cut back to heights and on dates indicated in Table 1. PMN seed produced on Tift 23[A.sub.1][E.sub.1] were harvested by a plot combine and by hand to recover the majority of the seed. Statistical analyses of seed yields were not possible in most years (except 1988) because each of the five blocks was used to test a different napiergrass defoliation techniques and/or bird control techniques.

Table 1. Treatment regimes used to produce a pearl millet X napiergrass hybrid in Kunia, HI.
        Pearl millet-Tift 23[A.sub.1][E.sub.1]
Crop
year   Seeding date   Seeding rate     Row width
                      kg [ha.sup.-1]      cm
1985   07 Oct. 85         3.5             53
1986   25 Sep. 86         5.6             35

1987   16 Sep. 87         4.5             35
1988   16 Sep. 88         4.5             35

                PMN seed             Napiergrass cut-back
Crop          harvested on
year   Tift 23[A.sub.1][E.sub.1]   Height               Date

1985          3-4 Jan. 86          Ground level      04 Jan. 86
1986          6-7 Jan. 87          A. ground level   15 Aug. 96
                                   B. 1.2 in         25 Sep. 86
                                   C. ground level   25 Sep. 86
1987          15 Dec. 87           1.2 m             10 Sep. 87
1988           2 Dec. 88           1.2 m             09 Sep. 88


Results and Discussion

Observations in the 1985 establishment year indicated that the interspecific cross could be produced in Hawaii but that row width for the PM seed parent needed to be closer than 53 cm to take advantage of land space, and seeding rate needed to be increased to ensure a stand of PM. Row width was reduced to 35 cm for PM in 1986 and subsequent years. A seeding rate of 5.6 kg [ha.sup.-1] for PM in 1986 tended to produce thin-stalked plants that could lodge during a heavy rain storm. Therefore, the seeding rate was reduced to 4.5 kg [ha.sup.-1] in 1987 and 1988.

Three NG cut-back treatments (Table 1) in 1986 revealed that a 1.2-m height at (or near in subsequent years) the planting date of PM provided a good nick for the PM and NG. In 1987 and 1988, we moved the NG cut-back date from 25 September to 10 September and PM planting date from 25 September to 16 September so that PMN seed could be harvested in December.

The highest PMN seed yield (1145 kg [ha.sup.-1]) was obtained in 1986 (and subsequent years) when NG was cut back to 1.2 m at the time PM was planted on (or about) 25 September and the block was protected with a polypropylene net. In 1987, a block protected with a polypropylene net produced 651 kg [ha.sup.-1] PMN seed compared with 322 kg [ha.sup.-1] for an unprotected block. In 1988, four unprotected blocks produced 323 [+ or -] 42 kg [ha.sup.-1] PMN seed while a polypropylene protected block produced 589 kg [ha.sup.-1].

Polypropylene netting was the only effective control in this study for the spotted munia bird. The netting is not practical on a commercial scale, but some type of protection from this bird is necessary. The bigheaded ant was controlled with bait. Poor stands result if the ant was not controlled. Narrowing rows of PM from 53 cm to 35 cm helped to reduce weed severity. Heavy rains in November and December during seed maturity reduced harvested seed yield, reduced seed germination (which averaged about 50%) and caused sprouting in the inflorescences before harvest.

It appears that Kunia is not an optimal production site for producing the PMN hybrid for seed to mature in December because of the spotted munia bird problem and the high probability of wet winter storms. Based on 30-yr average weather data, there is a 1-in-4 chance of having a drenching 2-d storm in the critical 14-d grain filling period in late November and early December. The probability of a 2-d storm in March is about 1 in 8, therefore, studies are needed to determine the feasibility of producing the PMN hybrid so that seed can be harvested in March. The PMN hybrid may best be produced at a location in the tropics having a dry winter season.

The crossing system described above, was used successfully by the USDA Plant Materials Center at Hoolehua, Molokai, HI, to produce hybrids between the NG cultivar Bana and Tift 23[A.sub.1][E.sub.1]. Plants used in this study are being maintained at the Molokai Plant Materials Center and at the Kunia, Oahu, Substation, Hawaii Agriculture Research Center.

Acknowledgments

The authors acknowledge the Governor's Agriculture Coordinating Committee, State of Hawaii for partial funding of the project and Roger Styan for managing the research plots at the Kunia Substation, Hawaii Agriculture Research Center.

Abbreviations: CMS, cytoplasmic male sterile; IVDMD, in vitro dry matter digestibility; NG, napiergrass; PM, pearl millet; PMN, pearl millet X napiergrass hybrid.

References

Boddorff, D., and W.R. Ocumpaugh. 1986. Forage quality of pearl millet X napiergrass hybrids and dwarf napiergrass. Soil Crop Sci. Soc. Florida 45:170-173.

Burton, Glen W. 1944. Hybrids between napiergrass and cattail millet. J. Heredity 35:226-232.

Hanna, W.W., and W.G. Monson 1980. Yield, quality and breeding behavior of pear millet x napiergrass interspecific hybrids. Agron. J. 72:358-360.

Hanna, W.W., and G.W. Burton. 1985. Registration of pearl millet inbreds `Tift [B.sub.1][E.sub.1]' and `Tift 23[A.sub.1][E.sub.1]'. Crop Sci. 25:366.

Powell, J.B., and G.W Burton. 1966. A suggested commercial method of producing an interspecific hybrid forage in Pennisetum. Crop Sci. 6:378-379.

Schank, S.C., and D.P. Chynoweth. 1993. The value of triploid, tetraploid and hexaploid napiergrass derivatives as biomass and (or) forage. Trop. Agric. (Trin) 70:(1)83-87.

R. V. Osgood, W. W. Hanna,(*) and T. L. Tew

R.V. Osgood and T.L. Tew, Crop Science and Genetics and Pathology Dep., Hawaii Agric. Res. Center (Formerly Hawaiian Sugar Planter's Association), 99-193 Aiea Hts. Drive Aiea, HI 96701; W.W. Hanna, USDA-ARS, Coastal Plain Exp. Stn, Tifton, GA. Received May 13, 1996. (*)Corresponding author (Forage@Tifton.CPES.Peachnet.Edu).
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Author:Osgood, R.V.; Hanna, W.W.; Tew, T.L.
Publication:Crop Science
Date:May 1, 1997
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