LOMAS DE ZAMORA, BUENOS AIRES, ARGENTINA

Universidad Nacional de Lomas de Zamora

LLAVALLOL, BUENOS AIRES, ARGENTINA

Universidad Nacional de La Plata

RÍO CUARTO, CÓRDOBA, ARGENTINA

Universidad Nacional de Río Cuarto.

Genetic variation in the progeny of maize/Tripsacum hybrids. --García, MD, Bonamico, N, Di Renzo, MA, Molina, MdelC According to Burson et al. (Crop Sci. 30:86-89, 1990), the form of apomixis in polyploid Tripsacum species is diplosporous pseudogamy of the Antennaria type, with complete absence of meiosis, which produces progeny genetically identical to the female parent. Nevertheless, Leblanc et al. (Theor. Appl. Genet. 90:1198-1203, 1995) observed the formation of meiotic dyads and tetrads amongst the diplosporic accessions of this genus. Kindiger and Dewald (Crop Sci. 36:250-255, 1996) evaluated the progeny of tetraploid T. dactyloides by cytogenetic and molecular (RAPD-PCR) analysis and observed complete absence of sexual development and genetic variation in the progeny. They suggested that an incomplete sexual process could originate this variation.

The objective of this work has been to determine the form of reproduction of the hybrid between maize and Tripsacum by means of cytogenetic and molecular analysis of its progeny.

Maize inbred 407B (2n=40) was pollinated with T. dactyloides (2n=72). Hybrid embryos (ZT56) were isolated and cultured on the basic medium (MD García et al., Rev. de la Fac. de Agron. de la UNLP 68:15-25, 1992) supplemented with 4 mmol L-1 2,4-Dichlorophenoxyacetic acid (2,4-D). Shoots were regenerated by somatic embryogenesis or organogenesis and rooted on the same basic medium without 2,4-D. Progeny was obtained by free pollination with Zea mays ssp. mays (2n = 20 or 40), Z. perennis (2n = 40) and Z. diploperennis (2n = 20). Seeds from ZT56 plants were germinated in sand and 8 days later coleoptiles have been cut off and soaked in 50 ml of extraction buffer L-ascorbic, tris-ClH 0,2 M, pH 7. The protein extract was absorbed on Whatman paper N3 and separation was performed by horizontal starch gel electrophoresis technique. Enzymes analysed were glutamic-oxalacetic transaminase (GOT), endopeptidase (ENP), esterase (EST), alcohol dehydrogenase (ADH), malate dehydrogenase (MDH) and acid phosphatase (ACP). The corresponding band pattern was settled for each sample constituted by a single seed taken from the same plant. According to the criteria of absence (-) or presence (+), the bands were enumerated from the anode to the cathode, B1 being the faster band.

Pollen of regenerated ZT56 plants was completely sterile, so some seeds were obtained from free pollination with maize, Z. perennis and Z. diploperennis. Every progeny plant revealed a chromosome number 2n=56, like the mother plant; consequently, the occurrence of a sexual process could be discarded. But, on the other hand, the molecular analysis showed variations within the progeny. GOT, ENP and EST enzymes showed monomorphism, whilst polymorphism was observed in MDH, ACP and ADH (Table). These results are similar to those published by Kindiger and Dewald (Crop Sci. 36:250-255, 1996) in tetraploid T. dactyloides. In the same way, the maize/T. dactyloides hybrid showed absence of sexual development, but the apomictic mechanism was able to generate genetic changes in the progeny.

Table. Isozyme profile from seedlings of ZT56 hybrid progeny. Polymorphism can be observed in MDH (band 1), ACP (band 4) and ADH (band 1).
 
Plant Enzyme
  MDH ACP ADH
  B1 B2 B3 B4 B5 B6 B7 B1 B2 B3 B4 B5 B6 B1 B2 B3
1 - + + + + + + + + + - + + + + +
2 + + + + + + + + + + - + + - + +
3 + + + + + + + + + + - + + + + +
4 - + + + + + + +   +       + + +
5 - + + + + + + + + + - + + - + +
6 - + + + + + + + + + + + + - + +
7 - + + + + + + + + + - + + - + +

 


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