Maize Genetics Cooperation Newsletter 80. 2006.

TURDA, ROMANIA

Agricultural Research Station

Effects of the Ht1 or Ht2 gene in five maize inbred lines on quantitative resistance to Exserohilum turcicum

--Has, V; Nagy, E; Has, I

A nonreciprocal factorial set composed of the recurrent parents (T248, T243, Lo3, N4, W153R) and five nearly isogenic lines, each carrying the Ht1 or Ht2 gene, were evaluated for quantitative resistance to Exserohilum turcicum under artificial inoculation with isolates from Turda and Fundulea and under a very strong natural infection by means of vegetative remains in soil in 2003 and 2004. Field studies were conducted to determine the effectiveness of the Ht1 or Ht2 gene in conditioning resistance to E. turcicum. Percentage of leaf tissue blighted was significantly lower for hybrids with the Ht1 gene than for hybrids made from their recurrent parents without the Ht1 and/or Ht2 gene when inoculated with isolates �Turda� and �Fundulea�, except Lo3 Ht1 x T248 Ht2 (Table 1). Hybrids with the Ht1 gene, except T243 Ht1 x N4 Ht1_, had significantly higher grain yield than the same hybrids without the Ht1 gene under inoculated conditions. The crosses with T243 Ht1 as maternal parent had significantly fewer lesions and shorter lesions than for its near-isogenic counterpart T243. Significant grain yield differences were detected between: T243 Ht1 x N4 and T243 x N4, T243 Ht1 x W153R Ht1 and T243 x W153R , T243 Ht1 x Lo 3 Ht1 and T243 x Lo3, Lo3 Ht1 x T243 and Lo3 x T243, Lo3 Ht1 x W153R. Percentage of upright plants was significantly higher for hybrids with the Ht1 or Ht2 gene.

When inbred lines were evaluated, reduced differences between original and Ht1 or Ht2 versions of the inbred lines T243 and T248 were detected. Conversely, W153R Ht1, Lo3 Ht1 and N4 Ht1 had higher disease efficiency than W153R, Lo3 and N4 (Table 2).

Results of this study indicate that generally Ht1 or Ht2 - converted hybrids are more resistant to E. turcicum isolates �Turda� and �Fundulea� than the original versions of these same hybrids. The difference was consistently significant, with the most susceptible hybrid being �ht ht�. This suggests that the level of quantitative resistance affects the expression of �residual resistance�. This study also indicates some maize hybrids and inbred lines with the Ht1 or Ht2 gene are more resistant to E. turcicum isolates �Turda� and �Fundulea� than near-isogenic hybrids without the Ht1 or Ht2 gene.

Table 1. An assessment of northern leaf blight, grain yield and upright plants on eight sets of four maize hybrids homozygous recessive, heterozygous, or homozygous dominant for the Ht1 and/or Ht2 gene following inoculation with E. turcicum isolates �Turda� and �Fundulea� in 2003 and 2004 at one location in Turda.

Hybrid	Leaf tissue blighted^1		Yield^2		Upright plants^3
	%	% of standard	q/ha	% of standard	%	% of standard
T243 x T248 T243 x T248 Ht2 T243 Ht1 x T248 T243 Ht1 x T248 Ht2	27.6 28.3 16.9 14.6	100 103 61 53	61.1 64.7 69.2 75.7	100 106 113 124	16.3 17.4 16.1 21.7		100 107 99 133
T243 x N4 T243 x N4 Ht1 T243 Ht1 x N4 T243 Ht1 x N4 Ht1	32.1 28.3 18.7 18.1	100 88 58 56	58.7 57.0 81.7 56.9	100 97 139 97	15.5 18.5 20.3 20.8		100 119 131 134
T243 x W153R T243 x W153R Ht1 T243 Ht1 x W153R T243Ht1 x W153R Ht1	27.1 15.4 10.3 10.3	100 57 38 38	58.5 69.1 67.3 71.1	100 118 115 121	22.7 22.0 26.3 22.7		100 97 116 100
T243 x Lo 3 T243 x Lo 3 Ht1 T243 Ht1 x Lo 3 T243 Ht1 x Lo 3 Ht1	31.0 28.1 14.6 13.7	100 91 47 44	55.1 58.2 82.2 78.9	100 106 149 143	18.0 22.1 28.7 35.0		100 123 159 194
Lo3 x T248 Lo3 x T248 Ht2 Lo3 Ht1 x T248 Lo3 Ht1 x T248 Ht2	19.6 20.3 18.1 20.6	100 104 92 105	67.1 68.2 61.7 73.1	100 102 92 109	22.0 27.4 29.8 32.4		100 125 135 147
Lo3 x T243 Lo3 x T243 Ht1 Lo3 Ht1 x T243 Lo3 Ht1 x T243 Ht1	29.9 17.7 28.8 16.7	100 59 96 56	55.1 69.3 63.4 69.9	100 126 115 127	24.6 30.3 21.7 26.9		100 123 88 107
Lo3 x N4 Lo3 x N4 Ht1 Lo3 Ht1 x N4 Lo3 Ht1 x N4 Ht1	25.3 16.9 22.6 16.3	100 67 90 64	59.9 67.9 66.3 69.2	100 113 111 115	13.1 25.1 18.1 26.7		100 192 138 204
Lo3 x W153R Lo3 x W153R Ht1 Lo3 Ht1 x W153R Lo3 Ht1 x W153R Ht1	22.1 11.7 15.2 9.4	100 53 69 42	53.4 54.0 64.9 61.0	100 101 122 114	45.1 65.4 55.7 66.5		100 147 124 147
Ht1 Ht1 Ht1 Ht1 Ht1 Ht1 Ht1 Ht1	26.8 20.8 18.1 15.0	100 78 68 56	58.6 63.5 69.6 69.5	100 108 119 119	22.2 28.5 27.1 30.7		100 128 122 138

LSD (0.05)⁴ 2.0 7.6 10.8

¹ Percentage of leaf tissue blighted 5 wk after the midsilk stage and area affected by the disease is based on visual estimates of leaf tissue blighted in the center row of three-row plots.

² Grain yields were adjusted to 15.5% moisture.

³ Percentage of upright plants were determined at harvest.

⁴ Percentage of leaf tissue blighted and upright plants were transformed with the arcsine transformation

Table 2. GCA and SCA effects for resistance to E. turcicum (percentage of leaf tissue blighted) under artificial inoculation with isolates from Turda and Fundulea.

Inbred line		T248	T248 Ht2	N4	N4 Ht1	W153R	W153R Ht1	GCA
								ht	Ht
T243		-5.5	-0.6	-6.1	1.1	-7.0	-2.7	9.5	4.6
T243 Ht1		3.5	2.1	2.2	6.0	1.7	5.6	-4.1	-5.1
Lo3		-6.9	-0.9	-6.3	-2.6	-5.4	1.3	2.9	-3.1
Lo3 Ht1		1.4	7.0	2.8	3.1	3.2	3.3	-0.8	-4.0
GCA	ht	4.2	4.9	9.3	3.2	5.2	-5.9	6.2	0.7
	Ht	-1.9	-1.8	1.2	-2.2	-6.7	-9.6	-2.3	-4.6

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