Hybrid F1s between maize and Tripsacum are very like Tripsacum, although they have a series of characteristics (pointed out by different authors) which make it possible to distinguish them from Tripsacum. It is important to be able to distinguish true hybrids from false ones, as they are very frequently obtained when pollinating maize with pollen of Tripsacum (patroclinous plants). If the cross is made using Tripsacum as female parent, matroclinous plants may be obtained. In order to distinguish Tripsacum in a quantitative manner from its hybrids with maize, we have made a series of measurements in inflorescences (Table 1).
Determinations were made on Tripsacum dactyloides (2n=72) and on hybrids which we had obtained in 1979 crossing an inbred line of maize carrying a floury-2 gene with Tripsacum. There are highly significant differences for the inflorescence characters. The number of branches (NB) in the terminal inflorescences is higher in hybrids than in Tripsacum. Hybrids have terminal inflorescences with a shorter rachis and a lower number of female spikelets. The width of fruit cases in hybrids (FCW) is significantly higher, and there is a lower number of fruit cases (FCN). In the lateral inflorescences the hybrid has a lower number of fruit cases and has less male (ML) and female (FL) length than Tripsacum. Also, as in terminal inflorescences, the hybrid has wider fruit cases in lateral inflorescences.
From these results it can be deduced that the maize germplasm contribution shows up in hybrid terminal inflorescences with a high number of branches, predominating in male spikelets. In the lateral inflorescences the hybrid has a tendency to differ less in male inflorescences. We have also seen that approximately 13% of the female spikelets in hybrids are arranged in pairs, as in maize. Likewise, hybrids have a longer period of vegetation and flowering than Tripsacum. In accordance with the results presented herein and those reported by other authors, the principal characteristics which distinguish the hybrid from Tripsacum are: (1) the hybrid has a higher number of branches in the terminal inflorescences; (2) a tendency in the hybrid to separate sexes in different inflorescences; (3) the absence or reduction in the number of female spikelets in terminal inflorescences in the hybrid; (4) terminal inflorescences in the hybrid with characteristics of the corn tassel or teosinte tassel; (5) in the hybrid, silks emerge before the inflorescence has emerged from the leaf sheath; (6) longer stigmas in the hybrid and the two branches of the style fused a greater distance than in Tripsacum; (7) fruit cases in the hybrid wider than in Tripsacum; (8) the hybrid has both single and paired female spikelets; (9) longer vegetative and flowering time in the hybrid; (10) a higher number of tillers in the hybrid; (11) larger size of leaves and stalks in the hybrid; and (12) full male sterility and high female sterility in the hybrid.
Jorge Luis Magoja and Ida Graciela Palacios
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