We attempted to hybridize Zea mays with Tripsacum with the object of studying the chromosome affinity between such species and the possible incorporation of some characters of the wild species into Zea mays. For this purpose, 100 ears of Zea mays (2n = 20) were pollinated with Tripsacum dactyloides 2n = 72), developing 400 shriveled seeds. Since they had not germinated by themselves, the mature embryos were cultured "in vitro." Development of some plants was obtained but only 3 of them survived after transplantation. Two were confirmed as hybrids because their somatic chromosome number was 46.
Morphologically the hybrids are similar to Tripsacum with slow growing at the beginning but with rapid development afterwards, flowering two years after implantation. Cytogenetic studies were carried out, obtaining the following results. In Tripsacum the meiotic configurations most frequently found were 26II + 5IV; 24II + 6IV; in Zea mays, as is known, 10II; and in the hybrid, 18II + 10I. In the hybrid, apparently the chromosomes of Tripsacum would pair by autosyndesis and the monovalents would correspond to Zea mays. In exceptional cases, 1 or 2 trivalents were observed, and frequently more than 10I were found. In Tripsacum, as well as in the hybrid, the chromosomes had large terminal knobs. Other chromosomes had joined themselves obtaining 6 or 7 "conglomerations" of knobs. In anaphase different numbers of chromosomes migrated to each pole, leaving some lagging chromosomes. The fertility of the pollen was 60%, but apparently viable seed could not be obtained.
From these preliminary studies on the hybrid Zea mays x Tripsacum dactyloides it can be concluded: (a) It is very difficult to obtain this hybrid, due to the fact that most of the developing seeds are the product of a parthenogenetic multiplication of the pollen of Tripsacum (patroclinous plants) and not true hybrids. (b) In the hybrid, in the chromosomes of Tripsacum dactyloides, the phenomenon of autosyndesis can occur, forming bivalents. (c) The chromosomes of Zea mays and Tripsacum dactyloides have not much homology since only occasionally were they partially paired.
Maria del Carmen Molina and Teresa Pilar Rosales
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