Field tests of toxin-resistant plants derived from tissue cultures of T-cytoplasm maize

This investigation was performed to further characterize the effect of selected Helminthosporium maydis (race T) pathotoxin resistance in maize plants regenerated from cell culture (Gengenbach and Green, 1975, Crop Sci. 15:645-649; Gengenbach et al., 1977, PNAS 74:5113-5117).

Bulked seeds were obtained for the following lines: A188(N), a non-sterile cytoplasm resistant to pathotoxin; A188(T) obtained from the cross Wf9(T) x W22 and backcrossed to A188(N) seven times. A188(T) is a Texas male-sterile cytoplasm (T-cms) susceptible to pathotoxin; A188(T-R2) traces to a toxin-resistant cell line-2 plant selected in tissue culture during the second backcross generation of A188(T) and has subsequently been backcrossed four more times by A188(N).

Experimental design was a randomized complete block with four replications at each of two locations. Field plot measurements included emergence, silking and pollen shedding dates, and percent germination. Five randomly selected plants/plot were either inoculated with H. maydis inoculum and pathotoxin or used to measure several morphological characters.

Nonsignificant differences were found for field plot measurements on emergence and silking dates (Table 1). A188(N) and A188(T-R2) responded similarly with respect to pollen shedding date and reaction to H. maydis pathotoxin and inoculum. The male-fertility and disease resistance traits associated with A188(T-R2) have been previously shown to be inherited only through the female (Gengenbach et al., 1977). Percent germination for A188(T-R2) was, on the average, higher than both A188(N) and A188(T).

Table 1. Field plot measurements and H. maydis pathotoxin/inoculum reactions.
Days1 to
Pathotoxin/inoculum reactions2
Genotype Emergence Pollen shed Silking
A188(N) 7.0 66.5 68.0 86.0 -
A188(T) 7.5 -3 67.5 84.5 +
A188(T-R2) 7.0 65.5 67.5 91.5 -

1Based on 50% of the total number of plants.
2As indicated by the presence or absence of chlorotic lesions.

Table 2. Total plant height, tassel culm length, and plant height above and below the ear (in centimeters).
Genotype Total hgt Tassel culm Hgt below ear2 Hgt above ear
A188(N) 159.1a1 54.1 47.1a 57.9a
A188(T) 147.2b 51.2 44.7b 51.3b
A188(T-R2) 153.8a 51.6 44.3b 57.9a

1Change in lower case letter indicates significance at the .05 level.
2Significant T-cms by environment interaction.

Tassel culm lengths for A188(N), A188(T), and A188(T-R2) did not significantly differ (Table 2). Environmental interactions were observed for plant height below the ear but A188(T-R2) was significantly shorter than A188(N). This result may be correlated with the significantly fewer number of nodes below the ear (Table 4). Total plant height and plant height above the ear for A188(T) was found to be significantly less than A188(N) and A188(T-R2). Because of nonsignificant node number above the ear (Table 4), height differences were primarily due to shorter internodes in A188(T) (Table 3). Significantly shorter internode lengths were observed for the three internodes directly above the ear and the internode immediately below the ear. Duvick (1965, Adv. Genetics 13:1-56) and others (Grogan and Sarvella, 1964, Crop Sci. 4:567-570; Josephson and Kincer, 1962, Crop Sci. 2:41-43) have indicated similar results with T-cms. Duvick also reported that plant shortening is enhanced by pollen sterility which in this case is caused by T-cms. The loss of pollen sterility observed in A188(T-R2) may partially explain the increase in plant height. Similar effects have been seen when T-cms was restored to fertility (Duvick, 1965; Sarvella and Grogan, 1965, Crop Sci. 5:235-238).

Table 3. Average internode lengths for plants with ears at the 5th node (in centimeters).
  Internode number
Genotype 1 2 3 4 5 6 7 8 9 10 11 12
A188(N) 12.0 12.4 12.2a1 11.1a 9.5a 11.2a  10.9 9.1 7.1 4.6 2.6 1.7
A188(T) 12.7 12.1 11.4b 9.8b 8.6b 10.3bc  10.4 8.7 6.6 4.6 2.4 1.2
A188(T-R2)  13.2 12.7 12.6a 11.2a 9.5a 11.1ac  10.1 8.9 6.7 4.2 2.8 1.8

1Change in lower case letter indicates significance at the .05 level.

Table 4. Average total number of tassel branches, leaves/plant, nodes below and above the ear, and total number of nodes.
Genotype  Tassel branches  Leaves/plant  Nodes below ear2 Nodes above ear Total
A188(N) 19.5 10.8a1 6.6a 5.3 11.8a
A188(T) 19.0 10.3b 6.2ab 5.0 11.2b
A188(T-R2) 19.5 10.1b 6.Ob 5.1 11.1b

1Change in lower case letter indicates significance at the .05 level.
2Significant T-cms by environment interaction.

Number of leaves/plant was based on the visible number of nodes/plant. A188(T) and A188(T-R2) gave similar responses but had significantly fewer leaves/plant than A188(N) (Table 4). Duvick (1965) reported a parallel situation based on the number of visible leaves in T-cms restored, nonrestored and normal cytoplasm.

Nonsignificant differences were observed for the number of tassel branches and number of nodes above the ear (Table 4). A significant environmental interaction was found for the number of nodes below the ear but A188(T-R2) had significantly fewer nodes than A188(N). Grogan and Sarvella (1964) found that differences in these characters depended on genotype and environment.

The effects of T-cms appear to be consistent with results previously cited in the literature. The response of A188(T-R2) was similar to A188(N) except for the number of nodes and internode length below the ear, total number of nodes, and number of leaves/plant.

P. F. Umbeck and B. G. Gengenbach

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

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