Trial plots of selfed parents, selfed F1, and F2 (F1 sibbed) from a diallel between local populations grown in summer 1986 showed an unusual frequency of chlorophyll abnormalities, mostly albinos. In spite of the fact that the experiment was not carried out for this purpose, the data on abnormality frequency and the population backgrounds would enable us to discuss the probable causes.
Five populations were used in the experiment. Punzo INTA is a commercial variety, obtained by stratified mass selection in 3:1 A synthetic in EERA Pergamino INTA (Sanguinetti, personal communication; for 3:1 A synthetic, see Illia et al., IDIA suppl. 32:32, 1976). BSR is the Syn-3 from the second cycle of recurrent selection for combining ability with the unreleased single cross ER x EX in 3 gene pools of the IFSC (Aguilar Riega, unpublished report). The remainder were unimproved stocks of the IFSC maize breeding programme.
The 5 populations and 2 others not included in the study were crossed in summer 1983 by one of us (F.J.B.) with bulked pollen, and the advanced generations of each cross were obtained in 1985. Composites of seeds from each generation of each cross were used for 2 yield trials in Llavallol and Chacabuco, Buenos Aires, in 1986. Abnormality frequencies only were taken in Llavallol. Data expressed in percent were analyzed using arc sin transformation, modified for zero percentage. Means of each entry were compared with suitable values for zero percentage (Table 1).
Table 1. Chlorophyll abnormal percentages in five populations and their
crosses in 1986-87.
Table 2. Chlorophyll abnormality percentages in five populations and
their crosses in 1987-88.
Rough estimates of heterozygous individual frequencies in BSR and Punzo were 30.14 and 7.4%, respectively. In the other populations selfed, abnormalities were not detected probably due to lower frequency that required a larger sample.
BSR x Punzo selfed, showed an intermediate abnormality frequency between those observed in the selfed parents. No abnormalities were observed in 4 crosses with BSR or Punzo, probably due to the low frequencies supposed in the other parents. All crosses between parents without evidence of abnormalities (BG x BHDC, BG x BCb, BHDC x BCb) exhibited these abnormalities. This could be explained by fixed alleles in different chlorophyll loci in each parent, and repulsion phase linkage in F1. Therefore the frequency of recessive homozygotes for any locus in selfed F1 was increased so it was easier to detect the abnormalities.
Seed stocks were increased in summer 1986, and the experiment was repeated in summer 1987, using mixed samples of seed of both years. Data of abnormality frequencies were also taken in Llavallol as during the previous year, and the analysis was performed as above (Table 2).
Abnormality percentages in BSR and Punzo were lower than in 1986; but we observed albinos in BHDC selfed and BHDC x BSR selfed. From F2, only BSR X Punzo showed abnormalities, although BHDC x BCb showed them in an additional trial with F2 and backcrosses. In this trial we also observed seedling abnormalities in (Punzo X BHDC) X Punzo and (BSR X Punzo) x BSR.
Selection in Punzo and BSR would have increased the frequency of heterozygous chromosome segments, marked by chlorophyllic abnormalities. Presence of different fixed alleles in the rest of the populations could be related to the divergence among them, and random fluctuations (genetic drift) due to assortative mating or effective population number during maintenance.
Francisco J. Babinec and Laura A. Pfluger
1Fellow of CONICET
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