| This form of vegetative reproduction exhibited by this strain of Aegilops
squarrosa could be considered to be apomictic because it appeared
to substitute for sexual reproduction which was almost completely absent.
The phenomenon bears implications for the potential survival of an annual
species such as Ae. squarrosa in certain unfavourable growing conditions,
as for instance the occurrence of unusual climatic conditions during growth
e.g. the rise of winter temperatures when the species germinates and grows
outside its normal growing season so that genotypes with strong vernalization
response do not have the response satisfied. Under these conditions normal
sexual reproduction can either be reduced or totally inhibited. The capacity
to develop axillary buds under such circumstances could confer regenerative
potential on the species by way of vegetative reproduction. As other reports have been made of environmental influences on the development of vegetative apomxis in plants GUSTAFFSON (1946) reported Malaxis paludosa (Orchidaceae), which occurs in Scandinavia, far north as 63o latitude had poor fruit-setting and its dispersal was mainly as bulbils formed from the leaves, while in Britain fruit-setting was normal. He also reported that Wolfia arrhiza (Lemnaceae) which occurs in Europe, Africa Asia and Australia reproduces vegetatively in the northern temperate zone and is without flowering but in warmer climates it reproduces sexually. SOYRINKI (1938) showed that the change to vegetative reproduction in phanerogram species in alpine vegetation of Petsamo-Lapland occurs mostly in the species whose primary habitat is not alpine. Environmental induction of apomictic agamospermy has also been reported in the Graminae. Short photoperiod was found to induce apomictic embryo sac development in Dichanthium aristatum (KNOX 1957), Themeda australis (EVANS & KNOX 1969) and Heteropogon contortus (TOTHIL & KNOX 1968). In the Tribe Hordeae apomixis as diplospory has been reported so far only in Agropyron scabrum in New Zealand (HAIR 1956 ; CONNOR 1979). It occurs either as a facultative or obligate expression in conjunction with forms with normal sexual reproduction (HAIR 1956). Literature Cited CONNOR, H.E. 1979. Breeding systems in the grasses : a survey. N.Z.J. Bot. 17 : 547-74. EVANS, L.T. and KNOX, R.B. 1969. Environmental control of reproduction in Themeda australis. Aust. J. Bot. 17 : 375-89. GUSTAFFSON, A. 1946. Apomixis in the higher plants. I. The mechanism of apomixis. Lunds Univ. Arsskr. N.F, ard. 2, 42(3) : 1-66. GUSTAFFSON, A. 1947. Apomixis in higher plants. II. The casual aspect of apomixis. Lunds Univ. Arsskr. N.F. Ard 2.43(2) :71-178. HAIR, J.B. 1956. Subsexual reproduction in Agropyron. Heredity 10 : 129-60. KNOX, R.B. 1967. Apomixis : seasonal and population differences in a grass. Science 157 : 325-6. MUNTZING, A. 1933. Apomictic and sexual seed formation in Poa. Hereditas 17 : 131-54. SOYRINKI, N. 1938. Studien uber die generative und vegetative Vermehrung der Samenpflanzen in der alpinen Vegetation Petsamo Laplands. Ann. Bot. Soc. Zool. Bot. Fenn. Vanamo. II. No. 1: 1- 311. STEBBINS, G.L. 1950. "Variation and Evolution in Plants" Columbia University Press, New York. 643 pp. TOTHILL, J.C. and KNOX, R.B. 1968. Reproduction in Heteropogon contortus. I. Photoperiodic effects on flowering and sex expression. Aust. J. Agric. Res. 19 : 869-78. |
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