The use of cytoplasmic male-sterility in maize seed production --Has, V, Has, I, Grecu, C The use of cytoplasmic male sterility (cms) in maize hybrid seed production is of economic importance and is also advantageous for genetic purity of seeds. Three types of male sterile cytoplasms in maize are used as cms maternal parents to produce hybrids: cms-C, cms-S, cms-T. The concern that in a few years all maize might again be in C or S cytoplasms gave rise to ideas as to how to prevent this narrowing of the cytoplasmic gene base. Thus, a new technique of producing hybrids was proposed, using multiplasm, respectively a blend of several kinds of male sterile cytoplasms. The aim of this investigation was: 1) to detect the presence of dominant Rf genes in more than 600 inbred lines by crossing with different types of cms: C, ES, M, T; 2) to compare some registered "TURDA" hybrids developed with normal and cms and/or Rf parental forms, in different environmental conditions, for three agronomic traits. Restoration reactions of 600 inbreds lines on the cms: C, ES, M and T were scored using Josephson’s scale (Josephson et al., 1978). The observations were performed at the Agricultural Research Station-Turda, between 1995-2001. Nine registered "Turda" hybrids carrying both fertile and sterile cytoplasms were grown in two years at five locations.

When using cms in maize breeding programs it is as necessary as it is difficult to identify the inbred lines by their composition of Rf genes. Identifying restorers of cms-C and cms-ES becomes much more complicated, due both to the involvement of at least two-three complementary Rf4, Rf5, Rf6 genes, and to certain modifying factors, probably quantitative ones which, in some specific environmental conditions, act in the absence of the Rf gene, influencing the reactions of lines by the "late-break" phenomenon. The percentage of non-restorer genotypes was 40% both to cms-C and to cms-ES (Table 1).

Table 1. The distribution of inbred lines according to their reaction in crosses to four cms types.
 
     
% inbred lines
 
cms

types

No.

cms tester 

lines

No.

studied

lines

Non restorers
Restorers
Different reactions
       
partially
fully
 
cms-C
5
198
34
4
55
7
cms-ES
3
94
35
5
51
9
cms-M
2
121
20
33
20
27
cms-T
7
223
74
1
16
9
Total-studied lines 636

121 inbred lines have been tested with cms-M, only 20% of them being identified as Rf3/Rf3. The inbred lines which partially restore fertility or have a variable reaction according to the environmental conditions represent 27% of the inbred lines tested with cms-M. Because cms-T is only used in areas less favorable to the disease caused by Helminthosporium maydis T-race, research on the use of this cms type is limited. Table 2 presents the synthetic results of the comparison between the cytoplasmic (N or cms) effects on certain agronomic traits of registered hybrids developed at the Agricultural Research Station, Turda, Romania. Trial conditions (years, locations) have emphasized a series of significant differences between the two cytoplasms as far as grain yield is concerned. These differences are greatly determined by nuclear-cytoplasmic interaction or by hybrid x local conditions interaction.

Table 2. Cytoplasmic male sterility effect for some traits in 9 registered "TURDA" hybrids.
 
Hybrid
Cytoplasms 
Grain yield q/ha
Dry matter of grain 

%

Erect plants at harvest

%

Synthetic relative index

%

1
2
3
4
5
6
Turda-SU 182 
N
98.6
76.6
85.4
100
 
cmsC
95.0
77.1
79.3
90
 
(%)cms/N
96
101
93
-
Turda-Mold 188
N
101.1
77.7
79.0
100
 
cmsC
97.3
77.9
81.8
100
 
(%)cms/N
96
100
103
-
Turda Super
N
85.1
75.3
81.6
100
 
cmsC
86.7
76.0
78.2
98
 
(%)cms/N
102
101
96
-
Saturn 
N
78.2
73.2
78.0
100
 
cmsC
92.1
75.1
83.2
129
 
(%)cms/N
118**
102**
107
-
Turda 215
N
97.5
76.0
73.5
100
 
cmsT
86.2
74.4
70.0
82
 
(%)cms/N
880
9800
95
-
Turda-SU 210
N
84.9
76.0
73.6
100
 
cmsC
89.2
77.0
75.8
110
 
(%)cms/N
105
101
103
-
Turda Favorite
N
93.3
75.8
80.7
100
 
cmsC
104.5
74.7
74.3
102
 
(%)cms/N
112*
99
92
-
Turda 198
N
102.1
76.8
76.1
100
 
cmsES
101.2
76.5
75.5
98
 
(%)cms/N
99
100
99
-
Turda 160
N
90.0
77.9
78.7
100
 
cmsC
87.8
77.1
81.2
97
 
(%)cms/N
97
99
100
-
Trial 
N
92.3
76.1
78.5
100
mean
cms
93.4
76.1
77.7
100
 
(%)cms/N
101
100
99
-
*** Significant at 5% and 1%, respectively
*Si%= {col.3x4x5(cms)/col.3x4x5(N)}. 100

The nine hybrids carrying cms did not differ generally from their counterparts with fertile cytoplasm (N) for yield and for two other traits.
 
 


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