BELGRADE-ZEMUN, YUGOSLAVIA
Maize Research Institute (Zemun Polje)
Changes in RFLP allele frequencies during recurrent selection for high oil content in maize --Lazic-Jancic, V, Ignjatovic-Micic, D, Markovic, K, Coric, T, Kovacevic, D, Saratlic, G, Quarrie, SA Although maize is not classified as an oil crop, oil production from maize has been increasing rapidly. To improve the efficiency of maize programs for increased oil content (i.e., to develop high oil hybrids of high yield and with other agronomically important characteristics) new breeding populations with favorable alleles for high yield have been developed (Micevic, D. et al., Crop Sci. 29:613-617, 1989; Dudley, J. W. and R. J. Lambert, Maydica 37:81-87, 1992).

Oil percentage is a quantitative trait controlled by many loci (Dudley, J. W. et al., Crop Sci. 17:111-117, 1977; Miller, R. L. et al., Crop Sci. 21:433-437, 1981). To help breeders introduce high oil content from such populations into elite lines, we have performed a study to identify genome regions carrying important genes for high oil content.

Genotypes used for this study were two maize populations, YuSSSu and DS7u, created at the Maize Research Institute, Zemun Polje. Selection for nine cycles resulted in a change in oil content percentage from 43.3gkg-1 to 128.7gkg-1 in YuSSSu and 47.2gkg-1 to 136.4gkg-1 in the DS7u population (Figure 1) (Dumanovic, J., 1995). By comparing allele frequencies in unselected (cycle 0) and selected (cycle 5 and cycle 9) populations by molecular markers (RFLP), it is possible to locate regions of the genome carrying genes determining oil concentration, thus identifying beneficial and/or detrimental alleles. The identification of RFLP loci that may be associated with selection for oil concentration by comparing population bulks, provides information complementary to RFLP mapping studies designed to identify quantitative trait loci for oil concentration.

Figure 1. Effect of selection for oil content in DS7u and YuSSSu synthetic populations (nine cycles of selection).

Seedlings of each population and each cycle were raised, and equal weights of 75 plants combined and extracted using CTAB buffer to give DNA bulks. After restriction with three different enzymes (EcoRI, BamHI and HindIII), DNA samples were resolved on agarose gels and Southern blotted.

Restricted DNA was hybridized with DNA probes and labeled by PCR using dig-11-dUTP. Detection was done with anti-digoxigenin, fab fragment, conjugated to alkaline phosphatase and chemiluminiscent substrate CSPD (Dig System Users Guide for Filter Hybridization - Boehringer Mannheim).

Twenty-three RFLP probes known to hybridize to loci distributed around the maize genome were examined. Major allele frequency differences were regarded as likely to be real when they were present in the majority of probe/restriction enzyme combinations.

The results have identified seven regions of the maize genome (Table 1) where major differences in RFLP frequencies had occurred in both populations during selection for high oil content. The example is shown in Figure 2. However, with the probe umc90, differences in allele frequencies were present in one population but not in the other. This indicates that the genetic control of high oil content may not be the same in both populations. If the genetic control is found to be different in two sets of populations, then this provides opportunities for increasing oil content yet further by combining beneficial alleles from both populations.

Table 1. List and effects of the RFLP probes used with DS7u and YuSSSu populations.
 
Probe
Chromosome
YuSSSu
DS7u
tub1
1
N
N
umc157
1
N
N
umc107
1
C
C
bnl8.45
2
C
C
umc6
2
N
N
umc5
2
N
N
umc49
2
N
N
umc32
3
C
C
umc102
3
N
N
csu25
3
N
N
umc31
4
N
N
npi386
4
N
N
umc66
4
C
C
npi409
5
N
N
umc90
5
C
N
umc59
6
N
N
umc65
6
C
C
umc21
6
C
C
umc38
6
C
C
npi220
8
N
N
csu31
8
N
N
php20075
10
N
N
bnl7.49
10
N
N
N - neutral effect
C - changes in allele frequencies during selction

We are currently testing further RFLP markers to study in more detail the genetic determination of oil content in the maize kernel. The identification of RFLPs associated with oil content may be useful in molecular-marker facilitated breeding programs (MAS) designed to develop high-yielding, high-oil maize hybrids.

Figure 2. Densitometric traces for pooled DNA from 2 maize populations before (C0) and after selection for high oil content (C5, C9) hybridized with umc66.
 
 


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