Relationship between pg 11 pg 12, earliness and modification of some parts of the plants

In MNL 51:4, 1977, A. Alvarez et al. reported differences in earliness of chlorophyll-deficient plants in comparison with normal plants of similar genetic background. The origin of these chlorophyll-deficient plants was from the crosses of one inbred with three other different inbreds. The chlorophyll-deficient plants were earlier than normal plants. The difference of the mean, measured from planting to pollen shedding, between stocks, ranged from 5.3 to 11.3 days. The comparisons were made mainly between sister inbreds, originated from segregating plants in generations S1, S2, S3. We suggested that this chlorophyll-deficient character could be used for practical purposes in order to match flowering time of inbred lines originally of different periods. Later observations indicated that the character is determined by two independent recessive genes. Professor E. H. Coe suggested to us the hypothesis that the character could be the pale green, pg 11 pg 12. In fact, the test for allelism with pg 11 pg 12 fits such hypothesis.

To know behavior of the character in different stocks and in relation with the degree of homozygosis of the background, the study was done on eleven inbreds with inbreeding coefficient from 75 to 98% and on two F2 from single crosses of inbreds of quite different origin. The measured characters were: number of days from planting to silking; plant height; number of internodes; length of internodes below the main ear; length of internodes above the main ear; number of ears per plant; and number of kernels per plant. Comparisons were made between pale green and normal classes. Each pair of classes corresponds to: (1) sister plants of the same segregating inbreds (10 inbreds); (2) sister sublines originated for segregating selfed plants of the last generation (1 inbred); (3) sister plants of the same F2 (2 stocks). The inbreds were planted on two different dates: May 30, 1977 and June 8-10, 1977. For the earliness character, the comparisons have been subdivided according to these two planting dates. Means and differences for sister plants of 10 segregating inbreds (1) and sister sublines of 1 inbred (2) were as follows:
 
Character Planting Normal (N) Pale green (PG) N-PG
Earliness

(days from

first 72.58 62.07 10.51***
planting to

silking)

second 68.61 61.14 7.47***
Plant height both 150.68 118.43 32.25***
Number of

internodes

both 15.25 12.42 2.83***
Length of

internodes

below ear

both 10 8.58 1.42
Length of

internodes

above ear

both 13.87 15.54 -1.67*
Number ears

per plant

both 1.84 1.51 0.33**
Number

kernels per

plant

both 699 458 241***

*p < 0.05; **p < 0.01; ***p < 0.001

Means and differences for sister plants of the same F2 (3) of 2 stocks were:
 
Character Normal (N) Pale green (PG) N-PG
Earliness 79.9 72.6 7.30***
Plant height 171.5 150.8 20.7**
Number of

internodes

14.52 12.40 2.12***
Length of internodes

below ear

10.66 10.33 0.33
Length of internodes

above ear

13.40 14.20 -0.80*
Number of ears

per plant

2.36 1.41 0.95**
Number of

kernels per plant

913 476 437***

*p < 0.05; **p < 0.01; ***p < 0.001

The pg 11 pg 12 genotype (1) enlarges the length of the internodes above the ear (p < 0.05); (2) on the contrary, reduces the length of the internodes below the main ear, (significantly in the inbreds but not in the F2 groups); (3) reduces all other characters (p < 0.01 to p < 0.001); (4) had slimmer stems and a greater susceptibility to lodging than the corresponding normal plants (observations not quantified). In conclusion, it appears that pg 11 pg 12 can be useful in seed hybrid production, synchronizing the flowering time of parents originally of different flowering periods.

Luis Bosch, Mariano Blanco, Angel Alvarez, and José L. Blanco


Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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