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USDA-ARS, P.O. Box 1090, Stuttgart, AR 72160
* Corresponding author (jnrutger{at}spa.ars.usda.gov)
The USDA-ARS released four indica rice genetic stocks (Oryza sativa L.): Early Plant Death, sometimes known as Apoptosis; Narrow Leaf, sometimes known as "Chives"; Extreme Dwarf; and Gold Leaf, Reg. no. GS-3 to GS-6, and PI 643128 to 643131, respectively, in May, 2006. These specialized seed stocks are expected to be useful to scientists conducting basic genetic studies in germplasm adapted to the U.S., and in some cases may be useful to breeders for identifying lines in breeding programs.
As part of the Genetic Stocks–Oryza (GSOR) Collection, four genetic stocks were selected from a gamma-ray mutagenized indica (300 Gy) M2 population grown at Stuttgart in 2003. The mutagenized line was an 8 d-earlier sib to the previously released germplasm line indica-9 (PI 634583) derived from the cross Zhe733/IR64 (Rutger et al., 2005). The earlier-maturing sib was chosen for mutagenesis in an effort to induce mutants that were even earlier in maturity; this effort was inconclusive. About 10000 seeds were mutagenized in late 2002 at each of two dosages, 250 and 300 Gy. The M1 generation was grown in the 2002/03 Puerto Rico nursery. Reduced seed set, an indication that mutagenesis had occurred, was observed in the 300 Gy treatment, so approximately 1000 M1 panicles were taken from that dosage. Twenty seeds from each M1 panicle were planted at Stuttgart panicle-to-row in the M2 generation in 2003, at a single seed per hill, in hills spaced 30 cm apart, in 30 cm wide rows.
The Early Plant Death mutant (GSOR 21) was observed in five out of 12 plants in a single M2 row. In subsequent tests, plant death began about 50 d after planting and concluded about 20 d later, with individual plants dying rather suddenly. Progeny testing in 2004 of the seven surviving M2 plants produced three segregating rows. In limited 2004/05 greenhouse progeny tests of normal M3 plants from a segregating row, one M3 plant that M4 progeny tests revealed to be heterozygous for the mutant phenotype was selected for further study. The progeny of this plant segregated 22 normal:13 dead, a satisfactory fit to a single recessive gene ratio (0.05 < P < 0.10). In 2005, progeny tests of 21 of the normal M4 plants revealed that seven were normal and 14 segregated for early death, a perfect fit to the expected 1 homozygous normal:2 heterozygous normal ratio. Also in 2005, further progeny tests of the original heterozygous normal M3 plant produced a segregation of 572 normal:190 dead, a near-perfect fit to a 3:1 ratio (0.95 < P < 0.975). In a sample of 100 or more grains, brown rice length, width and weight, from the surviving plants were 6.5 mm, 2.3 mm, and 20 mg, compared to 6.8 mm, 2.4 mm, and 22 mg for the parent genotype. Before the onset of the early death phenomenon, no phenotypic differences were evident between the mutant and the parent line. Residual seeds from the 14 heterozygous normal M4 plants were composited to provide a genetic stock which will segregate 3 normal:1 mutant.
The Narrow Leaf mutant (GSOR 22) was observed in two out of nine plants in a single M2 row. In subsequent tests, flag leaf dimensions of the mutant were 14.88 cm long and 0.56 cm wide, compared to 14.59 cm and 0.99 cm for the parent; other leaves on the mutant were reduced proportionately to the flag leaf reductions. In 2004 and 2005 progeny tests of the two M2 Narrow Leaf plants, all progenies were Narrow Leaf. In 2004 progeny tests of five normal M2 plants, two segregated for normal and mutant plants. In 2005 progeny tests using residual 2003 seed of one M2 plant that had segregated in 2004, segregation of 135 normal:32 mutant was observed, a satisfactory fit to a single recessive gene ratio (0.05 < P < 0.10). In a sample of 100 or more grains, brown rice length, width and weight of the mutant plants were 6.2 mm, 2.3 mm, and 18 mg, compared to 6.8 mm, 2.4 mm, and 22 mg for the parent genotype. No phenotypic differences between the mutant and the parent were observed for characters other than narrow leaves. Seeds of Narrow Leaf plants were composited to form a genetic stock that is true breeding for the narrow leaf mutant phenotype.
The Extreme Dwarf mutant (GSOR 23) was observed in five out of 11 plants in a single M2 row in 2003. In subsequent tests, the Extreme Dwarf plants averaged 24 cm tall compared to 80 cm for the homozygous tall sibs. In 2004 and 2005 progeny tests of Extreme Dwarf plants, all the progeny were Extreme Dwarf. In 2003/04 greenhouse tests of five normal M2 plants, three segregated for normal:mutant plants, 14:4, 10:9, and 14:5, for a pooled ratio of 38 normal:18 mutant, a satisfactory fit to a single recessive gene ratio (0.10 < P < 0.25). In a 2004 progeny test of the above three heterozygous M2 plants, the composite segregation ratio was 732 normal:246 mutant, again fitting a 3:1 ratio (0.90 < P < 0.95). In a sample of 100 or more grains, brown rice length, width and kernel weight from the mutant plants were 6.0 mm, 2.1 mm, and 16 mg, compared to 6.8 mm, 2.4 mm, and 22 mg for the parent genotype. Flowering time of the mutant was similar to the parent. Seeds of Extreme Dwarf plants were composited to form a genetic stock that is true breeding for the extreme dwarf mutant phenotype.
The Gold Leaf mutant (GSOR 24) was observed in two out of seven plants in a single M2 row in 2003. In subsequent tests, the gold, or bright yellow, leaf color appeared about 80 d after planting in the upper leaves and remained in the leaf material through harvest. In 2004 and 2005 progeny tests of the two original Gold Leaf plants, all the progeny were Gold Leaf. In 2004 progeny tests of four normal M2 plants, one was noted to produce five green and two Gold Leaf plants, six of which remained at harvest time. In progeny tests of these six remaining M3 plants in 2005, four segregated and two gave all green progenies, indicating that one green plant had been misclassified as gold in 2004 and another gold plant had been lost before harvest. The composite segregation ratio within the four segregating plants was 217 normal:70 Gold Leaf, a satisfactory fit to a single recessive gene ratio (0.75 < P < 0.90). In a sample of 100 or more grains, brown rice length, width and kernel weight from the mutant plants were 6.7 mm, 2.4 mm, and 21 mg, compared to 6.8 mm, 2.4 mm, and 22 mg for the parent genotype. Otherwise, mutant and normal plants were phenotypically similar. Seeds of the Gold Leaf plants were composited to form a genetic stock true breeding for the gold leaf trait.
Seeds of these genetic stocks have been placed in the Genetic Stocks–Oryza Collection and are available for distribution in 1/2 gram (about 20 seeds) amounts to geneticists, breeders and other research personnel on written request to: J. Neil Rutger, Dale Bumpers National Rice Research Center, USDA-ARS, and P.O. Box 1090, Stuttgart, AR 72160. Emailed requests may be sent directly to gsor{at}ars-grin.gov. Requests from outside the USA must be accompanied by an import permit. Genetic stocks also have been deposited in the National Center for Genetic Resources Preservation, 1110 S. Mason Street, Ft. Collins, CO 80521–4500. Seeds are available for research purposes, including development and commercialization of new cultivars. If any of these genetic stocks contributes to the development of new genetic information, germplasm, or cultivars, it is requested that appropriate recognition be given to the source.
NOTES
Received for publication July 31, 2006.
REFERENCES
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