Dichotomously branched and two-tassel plants were found as spontaneous mutants in three stocks of maize: K-851, local from Bulgaria; K-2847, Brazilian blue; K-2858, local from Afghanistan, and in two hybrids. For the short designation of this mutant the symbol "dib" is proposed. The attempt to maintain this character was successful only in K-2858 and the description below is concerned with this stock.
The expression of the mutant varies. Usually the stalks are divided into two branches at the 4-8th node above the ground, more rarely at the very base or near the tassel. Therefore the mutant character may easier be observed after the tasseling. As a rule both branches develop similarly. The leaves and the ears are formed both on the common stalk and on each of the branches. The plants branching lower as a rule have more leaves and ears. The mutants differ insignificantly from the normal individuals in plant height and size of the elements of the plant structure (leaves, ears, tassels), but they develop two times more male spikelets (in two tassels) and about one and a half times more leaves and ears than normal plants.
In order to determine the hereditary basis of this mutant the dichotomously branched plants were selfed, sib pollinated and outcrossed to normal lines and stocks. From 403 selfed progenies which were studied 80 consisted only of normal individuals. In 230 segregating progenies mutant plants made up under 20%, in another 83 about 25%, and in 9 about 50%. Only in one progeny all 19 mature plants were branched, but in the next selfed generation the usual segregation was observed. It should be noted that in the above-mentioned progeny 18 seedlings (from 40 planted seeds) were lethal (white and yellow-white). Most probably the lethal genotypes may have normal phenotypes.
In the sibbed progenies as well as in the F1 outcrosses, both when the mutants were used as female and as male components, segregation was the same. But in this material the number of branching plants was significantly less than in the progenies of selfing of mutants. The normal plants from the sibbed progenies and from F1 were selfed too. The majority of these progenies consisted entirely of normal plants and only about 20% of them contained rare mutants.
It is important to note that in the whole material besides two-tassel plants there were many other mutants such as: tasselless plants, defective seeds, and lethal seedlings, which complicated genetical analysis.
Cytological analysis of the two-tassel mutant had been undertaken and the results were published (Micu, V. E., and S. G. Kaptari, 1973. Dichotomous branching of stalk and the absence of tassel in maize caused by aneuploidy. Genetika 9 (4):5-11). Chromosome numbers in the root tips of normal and two-tassel plants were determined. It was found that the chromosome number in the somatic tissue cells varied from 20 to 22 and in addition fragments were observed. Thus preliminary genetical and cytological study showed that the two-tassel mutant is due to aneuploidy.
V. E. Micu
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