The values of the suction force vary depending on the plant�s water deficit which, in turn, is determined by the medium where the plant is being cultivated, the species and even by the genotype.
In this paper we want to analyse the relationship between the genotype and the suction force at the leaf�s level in different vegetation phases as a criterion of fast, early and efficacious selection of the maize genotypes (parental forms) with a good production capacity.
The suction force (S.F.)increases with the age of plants (Table 1), and this increase can be considered as being determined by the increase of the foliar surface and by the aging of the protoplasmic colloids (when the ability to retain water diminishes and the plant loses water more easily).
Table 1. The suction force in different phases of maize vegetation (atm.)
| Genotype | 10 leaves | Flowering | Grain filling |
| Lc 1 | 4.18 | 4.88 | 4.90 |
| Lc 2 | 3.96 | 4.08 | 4.81 |
| Lc 3 | 3.07 | 3.27 | 3.74 |
| Lc 4 | 3.15 | 3.45 | 4.06 |
| Lc 5 | 3.27 | 3.72 | 3.91 |
| Lc 6 | 3.25 | 3.81 | 4.1 |
| Lc 7 | 2.97 | 3.15 | 3.61 |
| Lc 8 | 2.68 | 3.07 | 3.48 |
| Average | 3.31 | 3.67 | 4.07 |
There are differences toward the average from one genotype to another for all 3 vegetation phases (Graph 1).
For Lc 1, Lc 5 and Lc 6 the increase of the suction force (S.F.) is higher from the ten leaf phase to the flowering period than from the flowering period to the grain filling phase, when despite the continuing growth of the leaves, drying of the basic leaves occurs, which diminishes the active foliar surface.
The values of the suction force at every phase show that Lc1 and Lc 2 lose water more easily, and as a consequence, present a higher sensitivity to drought and intense heat.
The genotypes that retain water the best are Lc 8, followed by Lc 7 which, even in the flowering period and in the grain filling period when the soil�s water deficit is very large due to the very high temperature, still have the lowest values of suction force.
This water retention by the plant could be a sign that the genotype has the capacity to turn to good use water in the metabolic processes, which in the end is found again in the production of grains obtained (Graph 2).
Before knowing the production capacity of a genotype it is important to know some physiological aspects that are more easily and more rapidly analysed in an early development phase. In the end, this information can be used in the selection work of the improver.
The correlation between the suction force in the 3 vegetation phases and the production capacity (ten leaf-grain yield: r = -0.403; flowering period-grain yield: r = -0.507; grain�s filling period-grain yield: r = -0.311), shows that the production potential of the genotypes studied increases in inverse proportion with suction force.
Once again we have confirmation of the fact that the production elements
are being finalized during the flowering period (r = -0.507). A complex
study of the plant�s metabolism in this vegetation phase could supply us
with signs that some characters are genetically controlled and determined,
such as the production capacity.
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