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Breeding Systems in Cortaderia (Gramineae)
H. E. Connor
Vol. 27, No. 4 (Dec., 1973), pp. 663-678
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2407199
Page Count: 16
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1) Cortaderia (Gramineae, Subfamily Arundinoideae) is predominantly a South American genus but with four species in New Zealand and one in New Guinea. Gynodioecism, an outbreeding system of hermaphrodite and male-sterile female plants, is characteristic of the genus. But the genus also includes species that deviate from gynodioecism. 2) In the morphologically advanced Section Cortaderia C. selloana and C. araucana are sexually reproducing, and the former behaves subdioeciously. In most of the species in this Section hermaphrodites are absent and the females reproduce by apomixis. Apomixis is considered to have evolved more recently than gynodioecism. 3) Male sterility, since its establishment in the genus, has become expressed in two morphogenetic levels, one characteristic of Section Cortaderia, the other of the remainder of the genus. Expression of male sterility is delayed till after the development of microspores in the latter and is almost immediate in the former. 4) Male sterility is digenically controlled in C. richardii, and the ratios obtained in hybrids between it and the three other New Zealand species indicate that the control of male sterility is identical in all four species. In C. selloana the results also suggest that that control is digenic but the system is not identical with that in the New Zealand endemics. 5) Pleiotropic effects of the male sterility genes are seen in gynoecium and caryopsis sizes, and sometimes in lodicule dimorphism. The absence of abundant lemmata hairs in hermaphrodites of species of Section Cortaderia is interpreted as a recent development and is linked with male fertility. 6) Factors that assist in the maintenance of females in natural populations in C. selloana are (a) seed set in females at least twice that of hermaphrodites (b) germination of seeds from females about 8-times that of seeds from hermaphrodites. These two factors alone give an estimated 16-fold advantage to females. Hermaphrodites, though they do produce some viable seeds, act primarily as a pollen source. In C. richardii the discrimination is nowhere as sharp, and females in families from outcrossed females are estimated to have something less than twice the fertility of hermaphrodites from the same cross, both however, are almost twice as vigorous as plants of both sex forms from either open-pollinated or selfed hermaphrodites.
Evolution © 1973 Society for the Study of Evolution