IWGO MAIZE INBRED LINES PRODUCTIVITY, TOLERANCE AND YIELD RESPONSE TO THE ECB Ostrinia nubilalis HBN. IN YUGOSLAVIA 1981 - 1994 RESULTS

Franja BACA
Maize Research Institute, Zemun Polje, Belgrade-Zemun, Yugoslavia

Resistance/tolerance of 359 maize inbred lines was tested in Yugoslavia within the common research work of the International Working Group on Ostrinia (IWGO) during the 1981-1994 period. Investigations, under agroecological conditions of Zemun Polje with fertile chernozem soil, were performed in two variants (one with plants artificially infested with four ECB egg masses "in black head stage" and another one with plants protected with granulated insecticide). Productivity and yield response to pest damage were obtained by comparing the grain yield between the two variants.

Table 1: Summarized Results of the promising IWGO Maize Inbreds Tolerant to the ECB

Category of Tolerance
Noof Inbr.
Gen. Dam.
Number of
Tunnels (cm/plant)
Yield g/plant
Yield Reduction
Larvae
Holes
Number
Length
"A"
"B"
1.0 - 2.0
7
1.8
5.3
7.0
4.0
22.8
49
58
15.5
2.1 - 3.5
71
2.8
6.0
8.4
4.4
26.8
52
73
28.8
3.6 - 4.0
34
3.8
6.1
9.0
4.3
25.8
50
66
24.2
Over 4.0
55
5.2
6.8
10.4
4.7
28.5
41
56
26.8
Yield Category
Noof Inbr.
Gen. Dam.
Number  of
Tunnels (cm/plant)
Yield g/plant
Yield Reduction
Larvae
Holes
Number
Length
"A"
"B"
25 - 50 g/pl.
61
4.1
5.7
9.0
4.3
24.9
30
40
23
51 - 75 g/pl.
62
3.8
7.0
10.3
4.8
30.7
44
61
27.9
76 - 100 g/pl.
30
3.5
5.7
7.9
4.4
26.0
58
86
32.6
> 100 g/pl.
14
2.9
6.0
7.5
4.0
23.8
99
133
25.6

The aim of this study was to confirm the hypothesis that genotypes of higher genetic yield potential can tolerate infestation with 30-50 eggs plant-1 without significant yield reduction.

The objectives of these aspects of investigations were: to evaluate the tolerance of all tested inbreds to ECB. To evaluate the productivity of the individual IWGO inbred. To evaluate the losses caused by ECB larvae in relation to the degree of tolerance.

Following the mentioned hypothesis data analyzed were general damage rating, yield and yield response of only 167 inbreds with yield above 25 g grain plant-1, i.e. of those with yield reduction under 50%.

Summarized results on yield of 167 inbreds provide the basis to compare general damage rating, plant productivity and yield response of infested and protected maize plants. Inbreds were selected according to general damage rating and grain yield. According to general damage rating they were classified into the following four groups: 1) 1.0 - 2.0 - tolerant, 2) 2.1 - 3.5 - medium tolerant, 3) 3.6 - 4.0 medium susceptible 4) > 4.0 - susceptible; while according to grain yield they were classified into the following groups: 1) 25 - 50 g plant-1 - moderately yielding, 2) 51 - 75 g plant-1 - highly yielding, 3) 76 - 100 g plant-1 - very high yielding, 4) > 100 g plant-1 - extremely high yielding.

The results show that seven out of 359 inbreds have a high degree of tolerance. They have the average general damage rating of 1.8 and moderate grain productivity of 49 g plant-1 and 58 g plant-1 under artificial infestation and chemical protection, respectively. Due to high borer infestation, their yield reduction was on the average only 15.5%. Grain yield within the category of medium tolerance and medium susceptible groups with 71 and 34 inbreds was at the same level in infested variants; 52 g plant-1 and 50 g plant-1. Corresponding yield of protected variants was significantly higher. Yield reduction was 28.8% and 24.2, respectively.

Some of superior IWGO inbreds, as well as a certain number of other inbreds, were selected to develop divergent synthetic populations within the breeding program implemented by the Laboratory for Entomology, Maize Research Institute, Zemun Polje.

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