Cleistogamy in Grasses

Abstract

Grasses display an extraordinary diversity of breeding systems-inbreeding and most forms of monoecism, dioecism, and apomixis are well represented (49, 50). Self-fertility and inbreeding are important in limiting the gene flow between populations and producing ecogenetic differentiation (2, 4, 27, 97, 159); preserving gene combinations that confer high fitness in a local environment (2, 72, 90); permitting fruit to be set after long-distance dispersal or when conditions for pollination are adverse (11, 90, 145, 162); and reducing or eliminating the costs of sex, while maintaining an adaptive advantage over asexuality (140). Cleistogamy (CL)-i.e. self-fertilization in an enclosed flower-intensifies these potential advantages of inbreeding; it may also be important in altering seed size, germinability, dispersibility, and susceptibility to fire and animal predation (27, 57, 133, 164). CL is an evolutionarily derived and complex syndrome of morphological, developmental, genetic, and environmental components. The variability in the expression of CL in grasses may be considered from the perspective of any one component or a combination of them. The structures adapted for the protection of aerially exposed, chasmogamous (CH) spikelets, florets, and fruits and for fruit dispersal are often either reduced in size and/or number or lost altogether. CL grass flowers often mature precociously, although the developmental or physiological basis for this heterochrony is generally unknown. Mendelian inheritance of structural differences that lead to CL flowering has been demonstrated in two cases (10, 129), and Clay (39) has shown that variations in the flowering mode in Danthonia are at least partly genotypic. At the same time, environmental variables such as the photoperiod (76, 77, 93), level of soil