Protogyny in the Cruciferae

Abstract

Protogyny, generally assumed to be rare or nonexistent in the Cruciferae, has been reported in at least 61 species belonging to 32 genera zn nine tribes. In Iraq 4 72 natural populations representing 91 species (nearly half the cruciferousflora) were examined, and 80 populations representing 24 species in 19 genera were found to exhibit protogyny. Protogyny is reportedfor thefirst time in 21 species and in the genera Diplotaxis, Savignya, Erucaria, Hirschfeldia, Neslia, Aubrieta, Sterigmostemum, and Sisymbrium. Protogyny, a term proposed by Hildebrand in 1867 (Rieger et al., 1968), is a mechanism that favors outcrossing by the maturation of the stigma before pollen is released in the same flower. Its effectiveness in promoting outcrossing depends on the time gap between the maturation of the pollen and the stigma. This may be two hours or less (Kerner, 1895) or two or three days (Riley, 1956; Al-Shehbaz, 1973). Protogyny is important for population survival when other mechanisms favoring outcrossing are lacking or inefficient or when the gene pool is reduced (Rollins, 1971). It has been reported in several species of Cruciferae that are predominantly autogamous (Riley, 1956; Titz, 1972; Hurka et al., 1976). In few cases, however, it has been observed in self-incompatible populations (Rollins, 1971; Stork, 1972). In the highly autogamous species the very small amount of outcrossing resulting from protogyny may be all that is needed to produce some genetic variation upon which natural selection may work. This low level of outcrossing has been estimated by Riley (1956) at 5% in Thlaspi alpestre. Although Bateman (1955) stated that there is no protandry, no protogyny, and no dioecy in the crucifers, these three mechanisms had been reported more than 55 years earlier. Protandry was first reported by Batalin in 1889 (Knuth, 1908) in Pugionium dolabratum Maximowicz. It has also been recognized in Hugueninia tanacetifolia (Linnaeus) Reichenbach (Stager, 1914), Cardamineflexuosa Withering (listed as C. silvatica) (Gunthart, 1917), Descurainia millefolia (Jacquin) Webb & Berthelot (Schulz, 1936), Streptanthus glandulosus Hooker (Kruckeberg, 1957), S. carinatus Wright and S. culteri Cory (Rollins, 1963), and Erysimum spp. (Snogerup, 1967). Dioecism, on the other hand, was first reported by Kirk (1899) in Lepidium sisymbrioides J. D. Hooker, L. matau Petrie, and L. kawarau Petrie, but, to my knowledge, it is not known elsewhere in the Cruciferae. Perhaps the first demonstration of protogyny in the Cruciferae was made by Muller in 1873 (Hurka et al., 1976). Hildebrand (1879) reported ' Biology, College of Science, University of Baghdad, Baghdad, Iraq.