While we were working with hybrids between diploperennial teosinte and maize, the fast and vigorous development of the hybrid plants in relation to their parents, especially diploperennial teosinte, really took our attention. The hybrids between maize and its wild relatives are generally heterotic in the extreme. Heterosis expresses itself through different morphological and physiological effects and it is especially related to the kind of maize used in the crossings.
Our observations let us realize that a simple experiment, carried through in an early stage, could probably be used to foretell the heterosis expressed in inter-specific hybrids. It flashed into our minds that the initial strength of the plants could be measured through different parameters of measurement to be able to associate them, in the future, with traits of the mature plants. We designed an experiment consisting in the breeding, under similar environmental conditions, of hybrids between Z. diploperennis and a sweet maize variety (Evergreen). Seeds of each participant (parents and hybrids) were germinated in flower pots. Measurements were made at 10, 15, 20, 25 and 30 days after planting for the three participants and on 80 individual plants (four repetitions) for each stage of development. During all the experiment, the flower pots were sprinkled with a nutrient solution. The traits measured in each stage of development were the following: shoot length (SL); root length (RL); shoot fresh weight (SFW) and dry weight (SDW), and root fresh weight (RFW) and dry weight (RDW). The results obtained are shown in Table 1.
At the beginning, maize has greater development than the others for the different traits studied. As the initial growth of the plant mainly depends on the weight of the original seed, it can be concluded that they agree with the experimental values obtained; the initial dry weight of the seeds is very different; diploperennial teosinte is only 55.1 mg, hybrids 78.7 mg and maize 176.1 mg.
These great initial differences give advantage to maize, and because of this it was considered inconvenient to express the results in such a way that they could be comparable. For the last column of Table 1, we therefore calculated the total dry weight increment (TDWI) on the base of the initial dry weight of the seeds. The value of TDWI, for each stage of development, is the result of subtracting from the total dry weight (shoot + root) the initial dry weight.
During the first half of the experiment the hybrid plants are as heavy as maize plants, and they have a greater content in dry matter. Afterwards, fresh weight and dry weight values are higher in hybrids than in maize. TDWI is always higher in hybrids, whatever stage we consider. This fact lets us deduce an upper efficiency in the elaboration of dry matter and a higher production rate, as the initial dry weight of the hybrid seeds was less than 50 percent those of maize.
A remarkable fact is the slow growing of diploperennial teosinte, opposite to maize. In spite of it, heterosis comes out again when they greatly overcome the most vigorous parent. At the end of the experiment, hybrids almost make twice the amount of total dry weight per plant than maize. The results obtained have a special meaning for being clearly demonstrative of the wide possibilities that wild germplasm presents and which are possible to be used, to increase the biological efficiency of maize.
J.L. Magoja and I.G. Palacios
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