Maize Genetics Cooperation Newsletter vol 85 2011

 

 

 

Three-factor inheritance of aleurone color speckling in Navajo RobinÕs Egg and Hopi Speckled open pollinated varieties of maize—summary of research performed in Urbana, Illinois.

 

            --Stinard PS, Goncalves Butruille M, Kermicle JL, and Sachs MM

 

            Various systems of aleurone color mutability in South American maize land races have been isolated and characterized.  Stippling produced by R1‑st alleles has been identified in Andean land races (Brink RA, unpublished; Williams WM. 1972. Variability of the R‑stippled gene in maize. Ph.D. Thesis, Univ. Wisconsin, Madison); sectoring induced by mutable alleles of the Enr1 r1 haplotype-specific aleurone color enhancer has been identified in northern South American land races (Stinard PS, Kermicle J, and Sachs M. 2009. J Hered 100:217-228; Gonella JA and Peterson PA. 1977. Genetics 85:629-645); and aleurone color marbling conditioned by an R1‑mb allele has been identified in Pisccorunto maize from Peru (http://www.maizegdb.org/cgi-bin/displayvarrecord.cgi?id=9017398).  Although exhaustive surveys have not been conducted, these previously described systems of mutability have not been reported in native North American maize land races.  Nevertheless, there are North American land races with systems of variegated aleurone color that have not previously been characterized.  We describe here the characterization of one such system: Three factor inheritance for aleurone color speckling found in two North American open pollinated varieties of tribal maize (see Goncalves Butruille et al., this MNL, for companion article).

 

            Seeds of the open pollinated variety Navajo RobinÕs Egg Corn (NREC) with purple aleurone color speckling on colorless background (Figure 1) were obtained from Abundant Life Seed Foundation, Port Townsend, Washington.  The sectors of speckling on kernels of NREC do not have well-defined borders, but are more diffuse and reminiscent of r1 mottling or the endosperm blotching of Pl1‑Bh.  Crosses of NREC to the open pollinated variety Hopi Speckled Maize obtained from Native Seed Search, Tucson, Arizona produced speckled kernels in both the F1 and F2, indicating that the speckling is due to the same system.  Initial crosses of NREC to aleurone color testers for a1, a2, c1, c2, and r1 produced full colored kernels, indicating complementation.  F2Õs of NREC with the Stock CenterÕs full colored aleurone (ACR) standard produced a very low frequency of speckled kernels, approximating a 63:1 ratio of full color to speckled.  To further characterize the nature of NREC speckling and to determine the number of genetic factors involved, test crosses were performed as follows:  NREC was crossed to a stock carrying the nonparamutagenic self-colored R1‑sc:124 allele (and all other genes needed for aleurone color) in a W22 background, and the F1 was backcrossed by NREC to generate test cross ears.  Kernel counts from the test cross ears indicated 7:1 segregation of full color to speckled aleurone (Table 1).  All deviations from 7:1 were nonsignificant at the 0.10 level.

 

            We hypothesized that the 7:1 test cross ratios observed were due to the independent assortment of three recessive triplicate factors, i.e. kernels need to be homozygous for all three factors in order to produce the speckled aleurone observed in the NREC line.  In order to test this hypothesis, full colored kernels from the test cross ears were planted, and the resulting plants were crossed again by NREC.  Kernels from these ears were scored for full color vs. speckled.  If the system involves independently assorting triplicate factors, we would expect to obtain 7:1, 3:1, and 1:1 ratios for full color to speckled on these second generation back cross ears.  The results are presented in Table 2.  Of 66 ears, 63 gave chi-square values that didnÕt differ significantly from 7:1, 3:1, or 1:1 ratios.  One ear gave a 3:1 chi-square significant at the .10 level, one ear gave a 3:1 chi-square significant at the .05 level, and one ear gave a 7:1 chi-square significant at the .01 level.  Given the population size, such deviations would not be unexpected.  Furthermore, based on independent assortment, the number of ears with 7:1, 3:1, and 1:1 ratios respectively would be expected to occur in a ratio of 1:3:3.  Our observed number of ears matching these ratios (13, 33, and 20), did not differ significantly from the 1:3:3 ratio (chi-square = 4.57).  Thus, the data from the second generation back cross ears match what would be expected for three independently assorting triplicate factors.

 

            In order to further characterize the NREC factors, crosses of NREC were made to various aleurone color tester lines, yielding interesting results.  As mentioned above, crosses of NREC to the Stock CenterÕs r1 tester (in M14/W22 background) produced full colored kernels.  Crosses of NREC to r1 introgressed into W23 also produced full colored kernels.  However, crosses of NREC to r1 introgressed into Oh43 produced speckled kernels.  This cross was repeated using an independent r1 wx1 Oh43 conversion, also producing speckled kernels in the F1.  From these results we deduced that the r1 locus is likely one of the factors involved in the speckling phenomenon, and that Oh43 is homozygous for the other two speckling factors, but M14, W22, and W23 are not.

 

            Test crosses of NREC to an Oh43 conversion of R1‑g produced 1:1 ratios of full colored to speckled kernels (1428 full color : 1384 speckled, 1:1 chi-square = 0.688, NS).  This confirms that Oh43 is homozygous recessive for two of the speckling factors, and the 1:1 segregation is due to segregation at the r1 locus (R1‑g vs. the R1 allele present in NREC, R1‑NREC).  Even though R1‑NREC behaves as a dominant for aleurone color in crosses to the Stock CenterÕs r1 tester in the absence of speckling factors, it apparently acts as a recessive relative to R1‑g and R1‑sc:124 with respect to response to NREC speckling factors.

 

            Test crosses of NREC to a W23 conversion of R1‑r produced 3:1 ratios of full colored to speckled kernels (746 full color : 266 speckled, 3:1 chi-square = 0.891, NS).  Test crosses of NREC to a W23 conversion of R1‑Randolph produced a 1:1 ratio of full color to speckled kernels (1499 full color : 1570 speckled, 1:1 chi-square = 1.642, NS).  Since the difference between these two stocks is the R1 allele and not the genetic background, we conclude that the W23 background is homozygous recessive for one speckling factor, and what differentiates between the 3:1 segregation and the 1:1 segregation is the R1 allele.  In other words, R1‑Randolph is susceptible to NREC speckling, but R1‑r is not.

 

            From these data, we conclude that speckling in NREC requires three factors:  a permissive (e. g. R1‑NREC or R1‑Randolph) allele at the r1 locus, and homozygous recessive factors at two other independent loci.   Thus the genotype of r1 ^Oh43 is r1 r1 fac1 fac1 fac2 fac2, where fac1 and fac2 represent recessive alleles at the two independent speckling loci.  NREC is R1‑permissive R1‑permissive fac1 fac1 fac2 fac2.  R1‑sc:124 ^W22 is  R1‑nonpermissive R1‑nonpermissive Fac1 Fac1 Fac2 Fac2; R1‑g ^Oh43 is R1‑nonpermissive R1‑nonpermissive fac1 fac1 fac2 fac2; R1‑r ^W23 is R1‑nonpermissive R1‑nonpermissive fac1 fac1 Fac2 Fac2; and R1‑Randolph ^W23 is R1‑permissive R1‑permissive fac1 fac1 Fac2 Fac2.

 

            Jerry Kermicle initially referred to a similar speckling phenomenon as ÒFour Corners mottlingÓ because it was identified in varieties of speckled maize from Native American open pollinated varieties from the Four Corners region of the Southwestern United States.  Studies in Wisconsin (see Goncalves Butruille et al., this MNL, for companion article) found that this speckling system requires a permissive r1 allele (the strongest effect being found among certain R1‑d haplotypes, although certain other haplotypes show a weaker effect) and two recessive factors named mot1 and mot2 for mottling factors.  Tests of allelism were performed in Urbana and revealed the NREC system to be identical to the Four Corners mottling system.  Separate mot1 and mot2 testers from Wisconsin were used to show that the COOPÕs W23 lines are homozygous recessive for mot1.  We all concur that the two independent factors should be called mot1 and mot2.


Figure 1.  Kernels on a self pollinated ear of Navajo RobinÕs Egg Corn.

 


Table 1.  Counts of full color (Cl) and speckled (spk) kernels from ears of the test cross:  [R1‑sc:124 X NREC] X NREC.

 

female parent

Cl

spk

7:1 c2

 

 

 

 

2003P-139-1

 231

 35

0.105

2003P-139-2

 331

 44

0.202

2003P-139-3

 255

 30

1.015

2003P-139-4

 241

 39

0.522

2003P-139-5

 312

 44

0.006

2003P-139-7

 363

 50

0.058

2003P-139-8

 269

 44

0.694

2003P-139-9

 337

 48

0.000

2003P-139-10

 288

 52

2.427

 

 

 

 

Totals

2627

386

0.267

 

 


Table 2.  Counts of full color (Cl) and speckled (spk) kernels from ears of the test cross:  [[R1‑sc:124 X NREC] X NREC] X NREC.

 

Female parent

Cl

spk

1:1 c2

3:1 c2

7:1 c2

 

 

 

 

 

 

2004-2705-1

257

80

92.964

0.2861

38.919

2004-2705-2

352

54

218.729

29.639

0.2381

2004-2705-3

289

98

94.266

0.0221

58.180

2004-2705-4

217

85

57.695

1.5941

67.589

2004-2705-5

172

23

113.851

18.135

0.0891

2004-2705-6

358

106

136.862

1.1491

45.399

2004-2705-7

409

142

129.381

0.1751

88.728

2004-2705-8

266

104

70.930

1.9061

82.411

2004-2706-1

184

178

0.0991

112.799

445.084

2004-2706-2

180

179

0.0031

118.337

458.149

2004-2706-3

149

22

94.322

13.429

0.0211

2004-2706-4

149

136

0.5931

78.457

323.213

2004-2706-6

254

89

79.373

0.1641

56.710

2004-2706-7

180

27

113.087

15.783

0.05591

2004-2706-8

319

108

104.265

0.0201

63.891

2004-2707-1

236

209

1.6381

114.518

483.316

2004-2707-2

311

113

92.462

0.6161

77.628

2004-2707-3

298

92

108.810

0.4141

43.852

2004-2707-4

197

66

65.251

0.0011

38.145

2004-2707-5

245

96

65.106

1.8071

76.384

2004-2707-6

168

168

0.0001

112.000

432.000

2004-2707-7

213

204

0.1941

127.259

505.730

2004-2707-8

227

218

0.1821

136.576

541.702

2004-2707-9

239

216

1.1631

122.550

508.800

2004-2707-10

355

122

113.813

0.0851

74.574

2004-2707-12

366

127

115.864

0.1521

79.261

2004-2808-1

87

91

0.0901

64.787

242.777

2004-2808-2

443

69

273.195

36.260

0.4461

2004-2808-3

243

249

0.0731

172.098

653.310

2004-2808-4

254

241

0.3411

148.122

592.638

2004-2808-5

284

38

187.938

29.917

0.1441

2004-2808-6

233

69

89.060

0.7461

29.565

2004-2808-8

182

79

40.648

3.8633

75.337

2004-2808-9

131

37

52.595

0.7941

13.932

2004-2808-11

231

210

1.0001

120.333

497.286

2004-2709-1

146

165

1.1611

130.548

467.653

2004-2709-2

277

99

84.266

0.3551

65.751

2004-2709-4

307

109

94.240

0.3211

71.407

2004-2709-5

303

86

121.051

1.7351

32.832

2004-2709-7

178

157

1.3161

85.422

361.723

2004-2709-8

197

225

1.8581

180.477

642.818

2004-2709-9

291

85

112.862

1.1491

35.112

2004-2710-1

186

186

0.0001

124.000

478.286

2004-2710-2

130

120

0.4001

70.533

288.057

2004-2710-4

223

83

64.052

0.7361

59.834

2004-2710-5

231

238

0.1041

165.806

627.239

2004-2710-6

217

84

58.767

1.3571

65.326

2004-2710-8

218

231

0.3761

167.502

622.717

2004-2711-2

279

93

93.000

0.0001

53.143

2004-2711-3

437

162

126.252

1.3361

115.862

2004-2711-5

314

41

209.941

34.254

0.2931

2004-2711-7

456

64

295.508

44.677

0.0181

2004-2711-8

288

45

177.324

23.432

0.3131

2004-2711-9

214

76

65.669

0.2251

49.815

2004-2711-10

284

103

84.654

0.5381

70.494

2004-2711-11

180

29

109.096

13.794

0.3621

2004-2711-12

421

58

275.092

42.456

0.0671

2004-2712-1

287

104

85.650

0.5331

71.056

2004-2712-2

162

56

51.541

0.0551

34.666

2004-2712-3

270

42

166.615

22.154

0.2641

2004-2712-5

324

118

96.009

0.6791

81.449

2004-2712-6

285

102

86.535

0.3801

67.937

2004-2712-7

125

134

0.3131

98.750

364.572

2004-2712-8

105

48

21.235

3.3142

49.824

2004-2712-9

264

20

209.634

48.845

7.7344

2004-2712-10

354

121

114.293

0.0571

73.097

 

1 p > 0.1  (NS)

2 p < 0.1

3 p < 0.05

4 p < 0.01

p < 0.001 (no highlight or superscript)

 

 

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