From the dent grain to the flint, sweet, popcorn, waxy, or floury, the breeders and the users have the possibility to choose in concordance with various industrial goals.
Corn with more and better quality protein for improved nutrition appears promising.
Both the grain yields and the content of raw protein in the grain are governed by a complex of genes, which can be expressed or not depending on the multitude of factors that act in the maize plant through the entire vegetative period.
The climatic conditions (temperature, rainfall) represent only a part of the factors that influence the metabolic processes.
In order to obtain commercial maize hybrids with a high content of raw protein, the breeder must know their parental forms (inbred lines) well.
In our study, we analysed the grain yield and the content of raw protein in the grain for 8 inbred lines over the course of 2 years (1998, 1999), with different climatic conditions, in order to use these genotypes as parental forms for commercial hybrids with a high content of protein.
The agricultural year 1997-1998 was an excessively rainy year, both in the cold period (October 1997-March 1998 = +52.8 l/mp. in comparison with the multiannual average) and in the maize vegetative period.
The rain separated two intervals of drought: the first, in the third week of June and the first week of July (Figure 1), when the development of the flowery parts and the flowering of the maize takes place; the second interval of drought, in the first and second weeks of August, when the development and the filling process of the grains takes place.
The thermic regime was the limiting factor prevalent in the production's realization. We can say that the thermic stress which the plants had been submitted to nullified the excess of rainfall to a great extent so that, after the flowering period, the plants dried off visibly because of the stifling heat (when the temperature was 38 C in the meteorology shelter and over 50 C at the level of soil and leaves).
In these circumstances, we can say that 1998 was an unfavourable year for the maize culture (droughty year). 1999 was a favourable year for maize culture.
In the period of maximum vegetative development, flowering and grain development (in June-July) the rainfall amount was excessive (Figure 2) and permits the realization of a good grain yield.
The difference between the grain yield of the two experimental years in the 8 genotypes (inbred lines) studied is obvious.
The drought year 1998 is a remarkable one from the point of view of production capacity. Lc 403 produced 31.6 q/ha, Lc 402 produced 28.4 q/ha, W153R produced 26.8 q/ha, and the lowest production was obtained in Lc 404 and Lc 406 (Table 1).
Table 1. The grain yield and the content of raw protein in the grain
The average production for the genotypes studied is 23.3 q/ha, in comparison with 35.7 q/ha in the favourable year 1999.
The inbred line Lc 406 still remains in 1999 a genotype with a low production potential, but has the highest content of raw protein (11.5 %) of all the genotypes studied.
Lc 3/Dxx has the highest grain yield (42.2 q/ha), but the content of raw protein diminishes in comparison with the drought year from 10.0 to 9.8 %.
If, in conditions of drought and water stress, the average grain yield is diminished by 35%, the content of raw protein in the grain will rise 4% in comparison with the average protein of 1999, a year favourable to maize culture.
Though in stress conditions, the maize plant accumulates a high quantity of protein (probably as a measure of protection), the correlation between the production capacity and the content of raw protein in grain is much better expressed in the circumstances of a year favourable to maize culture ( r=-0.568 ) in comparison with a drought year ( r=-0.456 ).
It is obvious that, for all the genotypes studied, the quantity of raw
protein rises in inverse proportion to the production capacity, so that
genotypes such as Lc 404 and Lc 406 can be used in maize improvement programs
as germplasm sources for the improvement of the content of raw protein
in the grain.
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