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|Title: ||Studies on the pollination biology and breeding systems of some genera with sympatric species in the Brazilian cerrados|
|Authors: ||Barros, Mariluza Araujo Granja e.|
|Supervisors: ||Gibbs, P. E.|
|Issue Date: ||1990|
|Abstract: ||Flowering phenology, floral strategies pollinator
activity and breeding system were investigated in 14 species
of the cerrado vegetation in Braeflia (DF), from April 1985
to April 1986 in Tabebuia caraiba (Mart.) Bur., T. ochracea
(Cham.) Standl.; Erythroxylum campestre St. Hil., E.
suberosum St. Hil., E. tortuosum Mart.; Diplueodon
crulsianue Pohl., D. oblongus Pohl., D. ramosissimus Pohl.,
D. roomarinifolius St. Hil., D. villosus Pohl.; Kielneyera
abdita Saddi, K. coriacea Mart., K. speciosa St. Hil. and K.
The species occur sympatrically, often only a few
meters apart, and conspecifics frequently occur in clumps.
The majority of the species flowered during the dry
season (May to August) except D. oblongue, D. villosue and
K. speciosa which flowered during the wet season (December
to March). Most of them flowered for several months except
Tabebuia (one month). The most frequent flowering pattern
was the "Cornucopian"' type, except for D. crulsianue and D.
Villosus which were "Steady-State" types. Most congeners
flowered synchronously, except K. speciosa which showed
Flowers of all species are pollen donors (Tabebuia and
Erythroxylum also have nectar rewards), but each genus
presents specific floral strategies; Tabebuia, Massflowering,
Erythroxylum, distyly and cauliflory, Diplueodon,
enantiostyly and Kielmeyera, andromonoecy.
Flowers were visited by a large spectrum of bees
(38spp. ) and Erythroxylum were also visited by wasps (16
app. ). However, each genus had particular pollen vectors.
Tabebuia; Centris and Bombus; Erythroxylum: wasps;
Diplueodon; Apia and Trigona; and Kielmeyera; Xylocopa,
despite the fact that other bees occur all year round.
Controlled pollination experiments (self-,
intraspecific-, interspecific crosses, tests for apomixis
and from untreated bagged flowers), revealed that all
species have a high outcrossing level and are selfincompatible.
Only E. campeatre (shrub), D. crulsianus and
D. villosus (hemixyles), showed some self-compatibility.
Fluorescence microscopy indicated that pollen tubes from
selfing and from interspecific cross pollinations were
blocked in the ovary, suggesting that the selfincompatibility
barrier operates late. Only in Erythroxylum
the blockage occurred in the stigma (Thrum flowers) or in
the style (Pin flowers).
Fruit-set number from hand-pollinations and from
natural pollination were low, but the former frequently
yielded a higher number of fruits than the latter. Low
fruit-set was associated with lack of resources allocated by
the maternal parent for fruit maturation. In addition, it
seemed that, in all species, many flowers were programmed to
be pollen donors only, since they dropped without any sign
of ovary enlargement even if they were hand-pollinated or
were frequently visited by pollinators.|
|Publisher: ||University of St Andrews|
|Appears in Collections:||Biology Theses|
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