The inclusion of microgametophyte selection in breeding programs can greatly improve the process of creation of the initial material of maize. It is determined by such characteristics of the male gametophyte as small size, a great number of pollen grains, the possibility of analyzing without damage to the maternal organism, and by data on the expression of a part of sporophyte genes in the period of gametophyte existence. The investigations on maize gametophyte selection confirm the efficiency of such an approach. The estimation of effects of genotypes on pollen tolerance to different environmental factors also requires attention because the ability to form a sufficient amount of pollen, the viability of the male gametophyte and other characteristics are important breeding characters. The elaboration of details of microgametophyte selection will permit carrying out such selection in prospective populations in the early stages of the breeding process.
We investigated the ability of pollen grains of 5 different lines of maize to germinate on artificial nutrient medium with the herbicide metholachlor=2- ethyl-6-methyl-N- (1-methyl-2-methoxi-ethyl)-chloracetanilide (commercial mark - Dual 960EC). Pollen was taken from field plants which were isolated at the beginning of flowering. The control germination medium included 150 g/l sucrose, 300 g/l calcium chloride, 100 mg/l boric acid and 6 g/l agar. The germination was carried out at 26-28 C. To the control medium was added 10 mg/l, 50 mg/l, 100 mg/l and 500 mg/l metholachlor. The data are shown in the table.
First of all it is necessary to remark that different genotypes differ in the percentage of pollen grain germination in the control. The greatest percentage was obtained for line 751, the other ones did not have a very high percentage of germination, which could be connected with genotypic peculiarities and also, maybe, with the specific reaction of genotypes to the weather conditions of the year.
Table. Effect of herbicide metholachlor on the germination of maize
pollen grains in vitro.
| Treatment |
|
||||
| 751 | Ul26 | 1620 | Al427/501 | Al4/217 | |
| Control | 54.78 | 13.22 | 11.50 | 9.83 | 7.75 |
| 10mg/l | 42.63*** | 12.3316.50* | 13.17 | 11.63** | |
| 50mg/l | 10.38*** | 3.78*** | 4.17*** | 2.33** | 1.56*** |
| 100mg/l | 0*** | 0.44*** | 0.83*** | 0.17*** | 0*** |
| 500mg/l | 0*** | 0*** | - | - | - |
As for line 751, which had the highest percentage of germination in
the control (54.78%), all concentrations of metholachlor significantly
reduced the percentage of pollen germination. For line Ul26, where the
percentage of germination in the control was 13.22, the effect of inhibition
was observed at a concentration of 50 mg/l metholachlor. For other genotypes
with a lower percentage of germination in the control the concentration
10mg/l had a stimulating effect and a significant decline was obtained
at the metholachlor concentration 50mg/l. The fall in the percent of pollen
germination put together for genotypes was 63.74-81.05% for concentration
50 mg/l and 92.78-100% for concentration 100 mg/l. However, the percentage
of pollen germination for all genotypes did not decrease at the same rate.
The smallest decreases, 63.74% and 92.78% for the two above mentioned concentrations,
were observed for line 1620 and the greatest, 81.05% and 100% for line
751.
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