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Dep. of Agronomy, Univ. of Nebraska, P.O. Box 830915, Lincoln, NE 68583-0915
* Corresponding author (idweikat2{at}unl.edu)
Pearl millet [Pennisetum glaucum (L.) R. Br.] NPM-5 (GP-39, PI 634546) and NPM-6 (GP-40, PI 634547), dwarf grain germplasms containing the A4 cytoplasmic-nuclear male sterile (CMS) system with its respective nuclear restoration gene (R4) were released by the Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln, in November 2003.
The A4 CMS system uses Pennisetum glaucum spp. monodii cytoplasm and shows no reversion to male fertility, which typically occurs at a low frequency with the widely used A1 CMS system. Since most germplasms completely maintain A4 sterility (Hanna, 1989), male-fertility restorers (R4) (Hanna, 1989) are rare and few have been made available in agronomically acceptable dwarf backgrounds. Developing A4 restorers in lines carrying A4 cytoplasm simplifies the selection of good restorer lines because the quality of the male fertility is self evident on the selected plants. Restorer lines developed this way are designated A4R4.
NPM-5 was developed by random mating 17 A4R4 parental breeding lines developed in the University of Nebraska-Lincoln (UNL) breeding program in 1999. These parent lines were developed from six selfed F1 hybrids (Tift 23DA4E x R4 restorers) and two open-pollinated bulks of an early generation 91M54026A4 line grown in the 1992 Puerto Vallarta, Mexico, winter nursery. The R4 restorer gene source used in the F1 hybrids and the open-pollinated A4 lines was from the same parental lines used in the development of NPM-3 (Andrews and Rajewski, 1995). Seeds from these hybrids were grown at Mead in 1992, and 79 fertile selections with complete seed set were selfed and evaluated in 1993. The best 26 selections (dwarf, panicle exertion, complete seed set, early to medium maturity, and stiff stalk) were grown in a winter nursery in Puerto Vallarta and evaluated for seed set, dwarfness, panicle size, and earliness. Selfed seeds from 17 lines with complete fertility restoration were planted in isolation nurseries for random mating at the High Plain Agricultural Laboratory, Sidney, NE, in 1994. Ten of the open-pollinated families were similarly selected and random mated in 1995 and 1996. Bulked seed from this population was grown, selfed, and selected at Lincoln, NE, in 1997. The best 30 S1 plants were random mated in isolation nurseries in 1998. Random mating and selection continued at Mead from 1999 to 2001. Harvested seed of the best 29 families was bulked for release in 2001. Experiments to evaluate fertility restoration at multiple planting dates were conducted at Mead in 2002. Pollen shed counts of NPM-5 indicated that 99 to 100% of the plants were male fertile. Topcrosses of NPM-5 on two A4 testers showed averages of 61 to 93% fertility restoration.
NPM-6 was derived by intermating 37 A4R4 parental breeding lines developed in the UNL breeding program. Parental lines were chosen for their completeness of selfed seed set, diversity in genetic background (including both R1 lines and B1 lines) and their agronomic traits suitable for Nebraska conditions. The A4 cytoplasm source used in developing these breeding lines was derived from Tift 23DA4E. The R4 restorer gene was derived from several inbred sources developed at UNL, including inbred lines used in NPM-3, which restores male-fertility on the A4 CMS system. Breeding line development began with the use of the A4 maternal parent in several crosses with various B lines and R lines (R1 and R4), followed by successive generations of selfing and selection to develop fully fertile A4R4 parental breeding lines. These 37 lines were intermated at Sidney in 1998 and at Mead in 1999. Thirty-six open-pollinated families were selected for pollen shed, complete seed set, dwarf height, panicle exertion, panicle size, early to medium maturity, and stiff stalk. These families were random mated at Mead in 2000 and 2001. Seeds harvested from the 28 maternal families were bulked for release.
Experiments to evaluate fertility restoration at multiple planting dates were conducted at Mead in 2002. Pollen shedding counts of NPM-6 indicated that 93 to 96% of the plants were male fertile. Topcrosses of NPM-6 on two A4 testers showed averages of 63 to 81% fertility restoration.
NPM-5 is a medium-early maturing, dwarf, tillering A4R4 germplasm with good panicle exertion that averages 66 to 104 cm in height at maturity. It flowers between 57 and 68 d after early June to early July plantings at Mead, and has a 4- to 9-d range between first plants flowering and the average flowering date for the germplasm. Grain yields from 1660 to 2870 kg ha–1 have been recorded. Hybrids with two seed parents showed heterosis levels of 14 to 69% among three planting dates, with the best hybrid yield of 3752 kg ha–1. Seed of NPM-5 is gray in color, variable in shape with 1000-grain weight ranging from 5.9 to 13.8 g. Panicle size ranged from 14 to 29 cm in length, with a mean of 21.6 cm compared with a mean panicle size of 19.6, 18.7, and 25.0 cm for NPM-1, NPM-2 (Andrews et al., 1995), and NPM-3, respectively. Panicle diameter ranged from 2.2 to 3.7 cm, with good peduncle exertion and segregation for bristled panicles. Insect and disease reaction of NPM-5 has not been determined.
NPM-6 is a medium-early maturing, dwarf, tillering A4R4 germplasm with good panicle exertion that averages 85 to 100 cm in height at maturity. It flowers between 58 and 69 d after early June to early July plantings at Mead, and has a 5- to 9-d range between first plants flowering and the mean flowering date for the germplasm. Grain yields from 1700 to 2670 kg ha–1 have been recorded. Hybrids with two seed parents showed heterosis levels of 0 to 51% across three planting dates, with the best hybrid yielding 3526 kg ha–1. Seed of NPM-6 is gray or white in color, variable in shape, with a 1000-gain weight ranging from 5.9 to 13.8 g. Panicle size ranges from 17 to 28 cm length, with a mean of 22.5 cm and a diameter ranging from 2.1 to 3.3 cm with good exertion. Insect and disease reaction of NPM-6 has not been determined.
NPM-5 and NPM-6 provide more diverse sources from which dwarf A4R4 restorer lines can be derived to better utilize the A4 CMS system for producing medium to medium-early maturing dwarf grain hybrids. Male parent lines with good restoration on the A4 system can be obtained from NPM-5 and NPM-6 through selection of desirable inbreds with good selfed seed set before testing for yield combining ability. Sources of identified dwarf R4 restorers have been limited for the A4 system, which is considered to have several advantages, including no male fertile reversions in male sterile lines and generally better seed set in single cross hybrids when compared with the currently used A1 CMS system. Limited yield performance tests of NPM-5 and NPM-6 topcross hybrids indicates the germplasms have fair to good combining ability for grain yield with medium-early maturity seed parents.
Seed of NPM-5 and NPM-6 will be available for research purposes from the Department of Agronomy and Horticulture, P.O. Box 830915, University of Nebraska, Lincoln, NE, 68583-0915.
NOTES
Journal Article No. 14884 by Univ. of Nebraska Agric. Res. Div. Registration by CSSA.
Accepted for publication March 31, 2005.
REFERENCES
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