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a USDA-ARS, Dale Bumpers National Rice Research Center, P.O. Box 1090, Stuttgart, AR 72160
b University of Arkansas Rice Research and Extension Center, P.O. Box 351, Stuttgart, AR 72160
* Corresponding author (jnrutger{at}spa.ars.usda.gov)
The ARS-USDA and the Arkansas Agricultural Experiment Station released KBNT lpa1-1 (Reg. no. GP-86, PI 632282), a low phytic acid mutant of rice (Oryza sativa L.) in April 2002. The mutant was induced by 
radiation of the Arkansas rice cultivar ‘Kaybonnet’ (KBNT) (Gravois et al., 1995). The phytic acid portion of seed phosphorus (P) in KBNT lpa1-1 is reduced from 71 to 39% and the inorganic portion of seed P is increased from 5 to 32%, with little effect on total seed P (Larson et al., 2000). Phytic acid P is poorly digested by humans and non-ruminant livestock, and also may interfere with nutritional uptake of minerals like calcium, zinc, and iron.
Approximately 4000 seeds of the parent cultivar Kaybonnet were treated with 200 Gy of rays in 1994. The M1 generation was grown at Stuttgart, AR, and about 1000 random panicles were harvested for a panicle-to-row M2 generation, part of which was grown in a 1994-1995 winter nursery. Panicles from eight or nine plants of each of 347 M2 rows were harvested for summer 1995 panicle-to-hill plantings. Bulked seeds from each of the 347 M2 rows were screened for the elevated inorganic P which is associated with reduced phytic acid content using a colorimetric test for inorganic P (Chen et al., 1956). In one row, seeds for low phytic acid were found. Examination of seeds at harvest from the nine M3 hills of this row showed that two hills apparently were homozygous for the low phytic acid mutation, three hills were heterozygous, and four hills did not have the mutation. In a subsequent mapping population derived from a cross between one of these homozygous mutants and the indica cultivar Zhe 733 (Wenchao and Guohai, 1991), segregations of F2 plants, as determined by F3 progeny tests, were 28 homozygous wild-type:81 heterozygous:28 homozygous mutant lines. These data fit (0.10 < P < 0.25) the 1:2:1 ratio for a single recessive gene for low phytic acid, which was designated lpa1-1. The lpa1-1 mutation was mapped to a 2.2-cM interval on chromosome 2L (Larson et al., 2000).
In the 1998 two-location Stuttgart Initial Test 7 (SIT7), KBNT lpa1-1 yielded 6680 kg ha–1 compared to 7050 and 7810 kg ha–1 for Arkansas check cultivars Katy (Moldenhauer et al., 1990) and Drew (Moldenhauer et al., 1998), respectively. KBNT lpa1-1 was similar to the two checks for days to heading and lodging, about 10 cm shorter in height, and slightly higher in percent whole milled grain. In the 1999 SIT5, respective direct comparisons of the mutant and its KBNT parent were 7100 versus 8000 kg ha–1 grain yield, 87 versus 86 d to heading, 112 versus 110 cm tall, zero lodging for both, 51 versus 52% whole milled grain, and 1.408 versus 1.473 g for 100 milled kernel weight. In the unreplicated Preliminary Tests at Stuttgart in 1999, three entries of KBNT lpa1-1 averaged 6990 versus 6680 kg ha–1 for two entries of the parent. Thus, on balance, yield of KBNT lpa1-1 was about 90% of standard Arkansas cultivars. Amylose contents of the mutant and its parent were both 220 g kg–1.
In a 1998 greenhouse screening, the pattern of reaction to seven blast isolates of KBNT lpa1-1 was identical to that of the KBNT parent, i.e., both were susceptible to isolates IB-33 and IE-1K, and resistant to isolates IB-1, IB-49, IC-17, IG-I, and IG-1. Thus, except for low phytic acid and the 10% yield reduction, the phenotype of KBNT lpa1-1 was essentially identical to the parent.
Germplasm amounts of seed (
5 g) of KBNT lpa1-1 may be obtained by writing to J. Neil Rutger, Dale Bumpers National Rice Research Center, USDA-ARS, P.O. Box 1090, Stuttgart, AR 72160. Seed also will be placed in the National Small Grains Collection, USDA-ARS, 1691 South 2700 West, Aberdeen, ID 83210, where it is available for research purposes, including development and commercialization of new cultivars. If this germplasm contributes to the development of new cultivars it is requested that appropriate recognition be given to the source.
NOTES
Accepted for publication June 30, 2003.
REFERENCES
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