Maize Genetics Cooperation Newsletter 80. 2006.

 

STUTTGART, GERMANY

University of Hohenheim

FREISING-WEIHENSTEPHAN, GERMANY

State Research Center for Agriculture

 

Variation for female fertility among haploid maize lines

--Geiger, HH; Braun, MD; Gordillo, GA; Koch, S; Jesse, J; Kr�tzfeldt, BAE

 

       Progress in in vivo haploid induction by specific pollinator genotypes (inducers) has made it possible to routinely produce large numbers of maternal haploid (H) plants.  Treating these plants with colcicine and selfing them leads to doubled haploid (DH) lines, which are highly efficient tools in genetic research and practical breeding (Eder and Chalyk, TAG 104:703-708, 2002; R�ber et al., Maydica 50, 2005, in press).

       Chalyk and Rotarenco (Plant Genetics 37:1382-1387, 2001) reported about a recurrent selection procedure based on H-plants as test units.  H-plants were grown in an isolated plot surrounded by diploid plants of the parental breeding population.  Seeds grown on H-plants fertilized with pollen from diploid population plants were used to establish the next selection cycle.  This was possible in 10-30% of the H-plants.  No information was given about the number of seeds obtained from these plants.  Since haploids in higher plants generally are female and male sterile, the expected number should be close to zero.  However, according to Chalyk (MNL 73:53-54, 1999) grain number may vary �between several and several dozen�.  In the present newsletter we are reporting about a multi-location field experiment in which we determined the seed set, thousand-grain weight (TGW) and grain yield of unselected H-lines.

       The genetic material for our study was kindly provided by three collaborating maize breeding companies.  It was derived from three elite dent single crosses adapted to the Central European climate.  In the first step, about 80 DH lines were produced from each single cross by means of in vivo haploid induction using the proprietary inducer line RWS as pollinator (R�ber et al., see above).  In the second step, each DH line was converted to the haploid stage by again using the before-mentioned technique.  Fifty-four to fifty-eight H/DH-line pairs per population had enough seed for evaluation in field experiments at three locations in Southern Germany (Stuttgart-Hohenheim, Eckartsweier/Upper Rhine Valley, Frankendorf near Freising), with two replicates in one-row-plots with 20 to 35 plants per row.  Because of large differences in vigor, H- and DH-lines were grown in different blocks separated by a mixture of inbred lines differing widely in flowering time.  DH lines were machine-harvested, whereas the ears of the H-lines were picked by hand and carefully threshed in the laboratory.  Grain yield per plant and TGW were used to calculate the number of grains per plant in the most fertile population (Pop I).

       Surprisingly, all H-lines showed a certain degree of female fertility.  Yet grain yield per plant was much lower than in the DH lines (Table 1).  Among the three H-line populations, one (Pop. I) showed a grain yield several times higher than the remaining two.  In all three populations, the maximal grain yield was three to six times higher than the population mean.  In Population I, the grain number per plant varied from 25 to 192 (Fig.1A).

       Seven H-lines excelled with almost complete seed set.  Thousand-grain weight also showed a large range of variation (Fig.1B)
Table 1.  Mean, minimum, and maximum values for grain yield per plant [g plant-1] in three F1-derived populations of random haploid and corresponding doubled haploid maize lines averaged across three locations in Southern Germany in 2004 (N = number of lines per population).

 

Pop.

N

Haploid lines

Doubled haploid lines

Mean

Min.

Max.

Mean

Min.

Max.

I

54

12.70

2.93

47.04

61.91

28.19

100.80

II

57

3.45

0.58

9.22

74.55

38.69

121.26

III

58

2.14

0.04

14.57

54.47

12.03

97.26

 

 

A

 

B

 

Figure 1.  Frequency distribution for (A) grain number per plant and (B) thousand-grain weight [g] of haploid lines in Population I averaged across three locations in Southern Germany in 2004.  Figures below the abscissa refer to class means.

 

averaging across locations to approx. 160g (Table 2).  No relationship existed between grain number per plant and TGW, whereas a strong correlation (r = 0.95, P = 0.01) occurred between grain number per plant and grain yield.  Seed samples from the most fertile H-lines had full germination capacity (data not shown).  Great differences existed between test sites for all three traits measured (Table 2).  Remarkably, seed set was more stable across locations than TGW and grain yield.

 

Table 2.  Mean performance of 54 random haploid lines from Population I at three locations in Southern Germany in 2004 (HOH = Hohenheim, EWE = Eckartsweier, FRA = Frankendorf).

 

Trait

HOH

EWE

FRA

Mean

Grain number per plant

65.32

90.70

84.96

80.32

Thousand-grain weight [g]

171.52

188.01

120.24

159.93

Grain yield [g plant-1]

11.01

17.16

9.92

12.70

 

       Almost all H-plants were absolutely male sterile.  Only occasionally were tassels observed with one or a few extruding anthers, some of which released traces of pollen when the anthers were squeezed between one�s fingers.

       In conclusion, our results revealed great genetic variation in female fertility among and between H-line populations derived from elite dent single crosses.  Several lines showed full seed set with normal-sized, germinable kernels.  Thus, the RS scheme proposed by Chalyk and Rotarenco (see above) indeed should work in many breeding materials.  Further research is needed to clarify the mechanism leading to fertile egg-cells in haploid maize plants.

 

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