Incorporation of opaque-2 into ‘UMI 1200’, an elite maize inbred line, through marker-assisted backcross breeding

Figures & data

Figure 1. General scheme of marker-assisted backcross breeding (MABB) for the conversion of normal maize inbred line UMI 1200 into QPM version using the donor VQL 1. RP: recurrent parent (UMI 1200); DP: donor parent (VQL 1); A: homozygous allele to recurrent; B: homozygous allele to donor; H: heterozygous allele. Three levels of selection were carried out in developing the QPM version of UMI 1200: (i) foreground selection to select the plants with target allele o2; (ii) background selection to recover maximum RPG recovery; (iii) phenotypic selection for agronomic traits and endosperm modification.

Figure 2. Foreground screening of F₁, BC₁F₁, BC₂F₁ and BC₂F₂ individuals of UMI 1200 × VQL 1 using umc1066 primer. (A) Foreground selection in F₁ individuals; lanes 1–16, F₁ progenies. (B) Foreground selection in BC₁F₁ individuals; lanes 1–16, BC₁ F₁ progenies. (C) Foreground selection in BC₂F₁ individuals; lanes 1–17, BC₁ F₂ progenies. (D) Foreground selection in BC₂F₂ individuals; lanes 1–17, BC₂ F₂ progenies. M: 100 bp ladder; P₁: UMI 1200; P₂: VQL 1.

Table 1. Segregation pattern of the o2 allele in backcross and selfed generations of cross UMI 1200 × VQL 1.

Cross	Generation	Number of plants genotyped	Genotypic class			χ^2	p-Value
			O2/O2	O2/o2	o2o2
UMI 1200 × VQL 1	BC1F1	232	102	130	–	25.488**	<.00001
	BC2F1	218	96	112	–	17.529**	<.00002
	BC2F2	158	39	98	21	13.240**	.001

**Significant difference (p < .01). The markers were significantly distorted from the expected segregation ratio (1:2:1).

Figure 3. Background selection in selected individuals. Amplification with: umc1710 in BC₂F₁ (A); umc2101 BC₁F₁ (B); umc1026 in BC₂F₂ (C); umc1060 in BC₂F₂ (D); umc1924 in BC₂F₂ (E); umc1827 in BC₂F₂ (F); umc2143 in BC₂F₂ (G); umc1857 in BC₂F₂ (H); umc1185 in BC₂F₂ (I); nc012 in BC₂F₂ (J). M: 100 bp ladder; P₁: UMI 1200; P₂: VQL 1; Lane 1: DBT4-1-/25-10/25-10/25-16; Lane 2: DBT4-1-/25-10/25-17/25-11; Lane 3: DBT4-1-/25-10/25-17/25-13. The plant was scored AA if it contains the UMI 1200 allele, as BB if it contains the VQL 1 allele and as AB if it contains both UMI 1200 allele and VQL 1 allele (i.e. heterozygotes).

Table 2. Recovery percentage of recurrent parent genome (RPG) in backcross populations of cross UMI 1200 × VQL 1.

Generation	Genotype advanced	% Recovery	Range of RPG % in selected foreground positive plants
BC1F1	DBT 4-1-1/25-10 DBT 4-1-2/25-7 DBT 4-1-7/25-9 DBT 4-1-9/25-10 DBT 4-1-10/25-17 DBT 4-1-11/25-20 DBT 4-1-13/25-18	74.2 73.1 72.1 73.8 70.7 72.6 73.3	62.1–74.2
BC2F1	DBT 4-1-1/25-2/25-4 DBT 4-1-1/25-7/25-18 DBT 4-1-1/25- 9/25-14 DBT 4-1-1/25- 10/25-10 DBT 4-1-1/25- 13/25-6 DBT 4-1-1/25- 10/25-17 DBT 4-1-1/25-20/25-12	83.0 84.2 83.2 92.8 84.1 91.3 86.2	82.4–92.8
BC2F2	DBT 4-1-1/25- 10/25-10/25- 16 DBT 4-1-1/25- 10/25 17/25-11 DBT 4-1-1/25- 10/25 17/25-13	96.6 92.4 95.4	87.4–96.6

Figure 4. Endosperm modification in kernels observed through transmitted light. Varying degrees of opaqueness indicate varying levels of endosperm modification; 25% modified seeds from the selected cobs were forwarded to the next generation from BC₂F₁.

Table 3. Recovery percentage for morphological traits of BC₂F₂ progenies in comparison with recurrent and donor parents.

Traits	VQL 1 (Donor)	UMI 1200 (Recurrent parent)	Developed QPM introgressed BC2F3 lines			Recovery percentage (%) for morphological traits
			DBT 4-1-1/25-10/25-10/25-16	DBT 4-1-1/25-10/25-17/25-11	DBT 4-1-1/25-10/25-17/25-13	DBT 4-1-1/25-10/25-10/25-16	DBT 4-1-1/25-10/25-17/25-11	DBT 4-1-1/25-10/25-17/25-13
Days to tasseling (days)	62.00	60.00	58.00	56.00	57.00	96.67	93.33	95.00
Days to silking (days)	66.00	62.00	60.00	58.00	59.00	96.77	93.55	95.16
Plant height	127.40	132.00	127.32	126.45	123.40	96.45	95.80	93.48
Ear height (cm)	61.30	81.00	73.90	70.85	72.40	91.23	87.47	89.38
Tassel length (cm)	26.20	33.00	29.75	30.20	28.20	90.15	91.52	85.45
Number of tassel branches	9.00	13.00	12.00	11.00	12.00	92.31	84.62	92.31
Leaf length (cm)	48.20	55.00	50.50	47.2	44.60	91.82	85.82	81.09
Leaf width (cm)	5.36	6.50	5.75	6.00	5.50	88.46	92.31	84.62
Cob length (cm)	11.60	14.20	13.10	12.2	12.70	92.25	85.92	89.44
Cob girth (cm)	10.20	13.30	12.00	11.6	10.50	90.23	87.22	78.95
Number of kernel rows/cob	12.00	14.00	12.00	10.00	12.00	85.71	71.43	85.71
Number of kernels per row	20.00	26.00	24.00	23.00	21.00	92.31	88.46	80.77
Cob weight (g)	92.30	118.40	1 109.10	106.40	103.40	92.15	89.86	87.33
100 Kernel weight (g)	19.65	26.00	23.60	22.00	23.00	90.77	84.62	88.46

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