Nature 249: 491-493. (May 31 1974)

Correlation between speed of pollen tube growth and seedling height in Zea mays L.
David L. Mulcahy

EVIDENCE of a correlation between gametophytic and sporophytic qualities could be useful because gametophytic competition is both frequent and severe in natural populations'. A statistically significant correlation has been found in Zea mays between the relative speeds with which pollen tubes penetrate the lengths of styles and the relative competitive abilities of the resultant zygotes2. This correlation was found in a study of mixtures of two pollen types when the sporophytic competition was limited to interactions between zygotes developing within a common inflorescence. It is therefore possible that faster growing pollen tubes allow a relatively early start in postfertilisation growth which accounts for the competitive superiority of the resultant zygotes, although there is a conflicting report3.

The present study was designed to test for correlations between relative speed of pollen tube growth and relative seedling weight, avoiding the possible influence of differences in time of fertilisation. Pollen types, of known tube growth rates, were each applied to separate inflorescences on plants of known genotypes. Five replications of each cross were made. All genotypes used were highly inbred and none of the crosses was a self pollination. The relative speeds of pollen tube growth were determined by the certation technique4, modified to allow quantitative expression of the results5.

From each of the 35 well-filled ears produced by the unmixed pollinations of the present study, 36 seeds were removed from the middle segment, avoiding the extreme sizes of apical or basal seeds. Seeds were weighed individually and planted singly in sand-filled pots 2 inches square in size. The environment was controlled at 22±1° C, 2,500 f.c., and daylength 18 h. Fourteen days after planting, seedlings were cut at ground level and weighed.

The data were subjected to partial correlation analysis with three variables: the relative speed of faster growing tubes', relative seedling weight and relative seed weight (see legend to Table 1). Partial correlation analysis tests for correlations between any two factors and, in effect, removes the influence of additional factors. Thus, in the present study, the value r12.3   refers to the correlation between the first two factors, relative pollen tube speed and relative seedling weight, when the influence of the third factor is removed (Table 2).

Table 1 Crosses made and the results observed.

Pair No. Inbred lines used
and their genotypes*
Number of well-filled
ears obtained
Relative speed
of faster pollen
Relative seedling weight†
from faster pollen
Relative seed weight‡
from faster pollen
1 BB = yy x 16 = YY 2 0.0017 0.928 0.988
BB = yy x 8 = yy 2
2 3A = yy x 1c = yy 1 0.0057 1.088 0.993
3A = yy x 6A = YY§ 3
3 BB = yy x 1c = yy 3 0.0088 0.938 0.988
BB = yy x 6A = YY§ 2
4 BB = yy x 16 = YY 2 0.0154 1.209 0.988
BB = yy x 3B = yy§ 3
5 BB = yy x 16 = YY 2 0.0108 0.996 0.978
BB = yy x BB = yy§ 2
6 BB = aa x 9c = aa 1 0.0198 1.183 1.049
BB = aa x BB = AA§ 3
7 BB = aa x 9A = aa 2 0.0300 1.697 1.008
BB = aa x BB = AA§ 3
8 16 = YYaa x 12 = AA 2 0.0281 1.148 1.021
16 = YYaa x 9 = laa§ 2
*Lines designated as BB were obtained from Dr Robert Briggs, now of Funk Seed International, Inc., Bloomington, Illinois.
All others were supplied by the Maize Genetics Cooperative.
†Average weight of seedlings resulting from fertilisations by gametes of the faster growing tubes divided by that from fertilisations
by gametes of the slower growing tubes.
†Average weight of seeds from fertilisations by gametes of faster growing tubes divided by that from fertilizations by gametes
of the slower growing tubes.
§Faster pollen of the pair.

The partial correlation between relative pollen tube speed and relative seed weight, r13.2= 0.566, is not statistically significant, nor is that between relative seedling weight and relative seed weight (r23.1 =  -0.241). The latter result does not indicate that relative seedling weight and relative seed weight are generally independent of each other, it just means that in this study, no statistically significant portion of the variation in one factor could be attributed to variation in the other factor. This is understandable in that a separate analysis of variance (not presented here) indicated that if each inflorescence receives pollen from only one plant, weights of seeds resulting from fertilisations by gametes of the relatively fast pollen tubes do not differ significantly from weights of seeds produced by gametes of relatively slow pollen tubes, a conclusion in agreement with that of Jones4.

Table 2 Correlation and partial correlation analyses for relative pollen tube speed, relative seedling weight, and relative seed weight.

r12 = 0.781*
r13 = 0.608
r23 = 0.355
r12.3 = 0.761*
r13.2 = 0.566
r23.1 = - 0.241
*Significant at the 5% level.
r12, correlation coefficient between the first and second factors.
r12.3, partial correlation coefficient between the first two factors with the influence of the third removed.

The partial correlation coefficient between the first factor, relative pollen tube speed, and the second, relative seedling weight, with the influence of the third, relative seed weight, removed is r12.3 = 0.76l, which is significant at the 5% level (d.f. = 5 with two variables) (ref. 5). This demonstrates that a significant number of genetic factors which are expressed in the gametophyte are also expressed in the sporophyte.

This statistically significant correlation between relative pollen tube speed and relative weight of the resultant seedlings cannot be due to differences in time of fertilisation because there were no interactions between the two types of zygotes. It also suggests that seedling vigour, a selectively important quality6, can be influenced by gametophytic competition.

This study was supported by a grant of the National Institutes of Health and, in part, by a grant from the National Science Foundation.

DAVID L. MULCAHY
Department of Botany,
University of Massachusetts,
Amherst, Massachusetts 01002

Received January 8, 1974.

  1. Hartl, D. L., Evolution, 24, 415 (1970).
  2. Mulcahy, D. L., Science, 171, 1155 (1971).
  3. Collins, G. N., and Kempton, J. H., US Department of Agriculture Bureau of Plant Industries Circ., 124 (1913).
  4. Jones, D. F., Selective Fertilization (Univ. Chicago Press, Chicago, Illinois, 1928).
  5. Crow, E. L., Davis, F. A., and Maxfield, M. W., Statistics Manual (Dover Publications Inc. New York, N.Y., 1960).
  6. Black, J. N., Aust. J. agric. Res., 9, 299 (1959).