Floral biology of four Ipomoea ( Tubiflorae : Convolvulaceae ) species

This research was carried out to evaluate the floral biology of Ipomoea acuminata, I. batata, I. cairica and I. quamoclit in Maringá, state of Paraná. Anthesis period, stigma receptivity, viability of the pollen grains and medium height of the style and filament were analyzed during the blossom period of Ipomoea. Both I. quamoclit and I. potato had their flowers opening at 6:00 a.m. and their closing at 2:00 p.m. The test of stigma receptivity demonstrated that I. quamoclit was receptive between 6:00 a.m. and 9:00 a.m. and I. batata between 6:35 a.m. and 1:00 p.m. The period of higher viability of the pollen grains in I. quamoclit was the same of the stigma receptivity. In that species, there was a reduction in the frequency of viable grains of pollen next to the time of the flowers closing. There were highest frequencies of viable pollen grains in I. batata between 6:35 a.m. and 7:00 a.m.; the variations in the frequency of viability of the pollen grains keep along the day until the flowers closing. In I. acuminata, the medium height of the style was 27.245 ± 2.431 mm and the medium height of the filament was 26.439 ± 3.147 mm. In I. batata, the medium height of the style was 19.77 mm ± 1.956 mm that is higher than the medium height of the filament. The medium height of the style in I. cairica was 19.827 mm and the medium height of the filament was 17.952 mm. In I. quamoclit the medium height of the style and the medium height of the filament had both bigger and smaller height variations of the style. For that species the estimated differences between the medium height of the style at 8:30 a.m. and the filament 1 and 4; and between the medium height of the style at 10:30 a.m. and filament 3, 4 and 5 were significant. For I. batata the differences between the medium heights of the style and of the filament were significant.


Introduction Introduction Introduction Introduction
The Convolvulaceae family presents wide distribution in tropical and subtropical areas.They are, in general, plant creepers, but they can also occur as bushes and small trees (Joly, 1994).Their species are classified in several categories as weed (Aranha et al., 1988;Lorenzi, 1991), medicinal plants, and it can also be used for human feeding.
Also, they can eventually be used to beautify fences and wires in gardens because of its goodlooking and colored flowers in bell form (Proctor and Yeo, 1972).
Palinologic studies reveal that this family shows registrations starting from approximately 65 million years ago (Roubik, 1992).These data are important to relate the evolution, in geologic time, of the plants with its respective pollinator agents.
Countless species of several weed families are found in Maringá because of its agricultural area.Among them, the "viola rope": I. cairica, I. aristolochiaefolia, I. purpurea and I. quamoclit.
The study of reproduction forms and pollination mechanisms of weed are essential because they provide important information for the elaboration of control programs (Blanco, 1972).
It is important to know the competitive ability of weed as it is a basic element for the integrated handling.Knowing that will allow to foresee the losses of income caused by them and also, what kind of practice can avoid these losses.(Oliver et al., 1976;Shurtleff and Coble, 1985).Rizzardi et al. (2004) verified that the incidence and the density of the "viola rope" in soybean crop increased in the last years, thus, reducing the productivity and harming the harvest.
The "viola rope" is an aggressive competitor that benefits itself from the presence of another weed in soybean crop.Rizzardi et al. (2004) verified that when there is 100% of "viola rope" in the soybean crop, the losses were of 54%.When there is "viola rope" only in euphorbia heterophylla, the losses are reduced to 25%.
In that way, this research was carried out to evaluate some aspects of the floral biology of Ipomoea acuminata, I. potato, I. quamoclit and I. cairica distributed in the Campus of State University of Maringá -UEM (Universidade Estadual de Maringá).

Material and methods
Plants from the family Convolvulaceae of I. acuminata, I. potato, I. cairica and I. quamoclit, in the Campus of State University of Maringá (UEM) were used.Maringá is in the northwest area of state of Paraná at 554 m of altitude and 23° 24' of south latitude and 51° 25' of longitude west with humid subtropical climate (type Cfa).The annual average temperature is 21.9°C and annual pluviometric precipitation of 1,500 mm with influence of cold fronts of the south area.
The flowers and fruits development were accompanied during one year.The flower buds were marked at random with numbered labels.These buds were accompanied through periodic observations, since the opening until the flowers withering and that time was considered like anthesis period.
The stigma receptivity to the pollen grains was evaluated in five flowers collected every two hours (from 7:00 a.m. to 5:00 p.m.), during the flowering.The presence of peroxidase enzyme reflects the stigma receptivity.The stigma was immersed into hydrogen peroxide (3%) and the bubbles were observed (Dafni, 1992).
In order to verify the pollen grains viability in the flowering period, five flowers from each treatment were collected every two hours (from 7:00 a.m. to 3:00 p.m.).Five hundred pollen grains were analyzed in each lamina, following the Radford et al. (1974) technique.For each species, the average height of the style and the filament of each flower was measured.
The averages were compared, using the Tukey test using GLM of SAS (Sas Institute, 1998).

Ipom Ipom Ipom Ipomoea acuminata oea acuminata oea acuminata oea acuminata
In Table 1, data show that the medium height of the style of the Ipomoea acuminata flowers was 27.245 ± 2.431 mm of a total of 53 measured flowers, while the medium height of the filament was 26.439 ± 3.147 mm.However, the medium height of the filament 4 and 5 (Table 1) is larger than the medium height of the style.In general, those results suggest that it should have a small incidence of selfpollination.In Figure 1, data show that the differences Acta Scientiarum.Animal Sciences Maringá, v. 27, no. 1, p. 137-143, Jan./March, 2005 between the height of the style and the filament were significant for Filament 1.In that case the filament was inferior to the style, suggesting that, in general, there are mechanisms that prevent the selfpollination.

Ipomoea potato Ipomoea potato Ipomoea potato Ipomoea potato
In Ipomoea potato the medium height of the style was 19,773 ± 1,956 mm that is higher than the average of the height of the filament (Table 2).Those results were confirmed with the test of comparison of averages between the medium height of the style and the filament.It demonstrates that the estimated differences are significant (Figure 2).Results showed that the flowers opening of I.
potato happens at 6:00 a.m. and the closing at 2:00 p.m.At 7:00 a.m.Apis mellifera was observed visiting the flowers.
The test of receptivity of the stigma showed that this was receptive between 6:35 a.m. and 1:00 p.m.
In Table 3, data show that the highest frequencies of viable pollen grains are between 6:35 a.m. and 7:00 a.m.Those results demonstrate that there are variations in the frequency of viability of the pollen grains, but this remains along the day until the flowers closing (Figure 3A).

Ipomoea cairica Ipomoea cairica Ipomoea cairica Ipomoea cairica
For Ipomoea cairica, collections of flowers were accomplished in three schedules along the day.These results suggest that in I. cairica the selfpollination could occur.According to Galleto and Bernardello (2004) this species are selfincompatible.

Results showed that in
In Figure 4, data show that the estimated differences were only significant between the medium height of the style and filament 1 at 11:00 a.m.

Ipomoea Ipomoea Ipomoea Ipomoea quamoclit quamoclit quamoclit quamoclit
In Table 5, data show that in two analyzed times of Ipomoea quamoclit, the medium height of the style in relation to the medium height of the filament have both bigger and smaller height variations of the style.
In Figure 5, data show that the average differences were significant between the medium height of the style at 8:30 a.m. in filaments 1 and 4; and between the medium height of the style at 10:30 a.m. in filaments 3, 4 and 5.The period of higher stigma receptivity was observed between 6:00 a.m. and 9:00 a.m.
In Table 6, results show that the period of higher viability of the pollen grains coincides with the one of stigma receptivity that is between 6:00 a.m. and 9:00 a.m.It is possible to observe in Figure 3B that along the day there are small variations in the viability of the pollen grains.It is interesting to point out that the frequency of viable pollen grains decrease mainly at 1:00 p.m. next to the time of the flowers closing (12:00 a.m., 1:00 p.m.) (Figure 3B).Acta Scientiarum.Animal Sciences Maringá, v. 27, no. 1, p. 137-143, Jan./March, 2005 The obtained results are similar to those found by Maimoni-Rodella and Rodella (1992), studying the floral biology of Ipomoea acuminata.Those authors verified that the flowers of that harmful species of Ipomoea also have anthesis diurnal period and they are ephemeral.However, the flowers open between 4:30 a.m. and 5:30 a.m., presenting the exposed pollen grains and the receptive stigma; the withering happens between 10:00 a.m. and 12:00 a.m.In that same work, the authors verified that when withering, the corolla suffers an enrollment towards the center of the flower, obstructing the entrance of the floral tube, coming off the following morning.
However, in Ipomoea acuminata the most frequent visitors are bees, but some Lepidoptera and Coleoptera are also observed.Regarding to Hymenoptera species of the families, Andrenidae, Anthophoridae, Apidae and Halictidae were registered.The most abundant and efficient species in the pollination belong to the family Anthophoridae; standing out Melitoma segmentaria (Maimoni-Rodella and Rodella, 1992).In that species the formation of 14 fruits was observed with normal and healthy seeds, happening therefore selfpollination in 56% of the tested flowers (Maimoni-Rodella and Rodella, 1992).These data suggest that the species is autogamic, benefiting also the visit of insects that promote certain proportion of crosspollination.This characteristic group is very frequent to the family of Convolvulaceae (Stucky, 1984;Maimoni-Rodella andRodella, 1986, 1986/87;Machado and Sazima, 1987).
The Ipomoea is weed and highly competitive plants with other weed species (Rizzardi et al., 2004).In this way, it would be interesting that these plants presented crossed breeding by means of pollination.This would lead to an ample genetic variability, contributing with its permanence in some types of environments.Morphometric data suggest that 4 analyzed species of Ipomoea have crossed breeding, probably pollinated by insects.Galetto and Bernardello (2004) evaluated the floral morphology and the composition of the nectar in 6 species of Ipomoea.The authors verified that there is not a correlation between these characteristics and the pollinators of these species.Nevertheless, nectar production dynamics and removal effects, with sugar composition, could not be clearly related either to the pollinator guild or to the breeding system of the species involved.The self-incompatible species are all bee-pollinated (I.hieronymi, I. indica, I. cairica) and they showed a similar total nectar production, but had differences in their nectar composition (I.hieronymi and I. indica are sucrose-dominant, whereas I. cairica is hexosedominant).The self-compatible species (I.alba, I. purpurea, I. rubriflora) showed no variation in nectar composition (sucrose-dominant nectars), but significant differences in their nectar production pattern.In contrast, flower length was associated with both nectar size and total amount of nectar produced.Recent studies suggest that flower morphology is evolutionarily more labile and that corolla traits can frequently change (Cubas et al., 1999;Harrison et al., 1999) in comparison to changes in the nectar features (Galetto et al., 1998;Perret et al., 2001;Torres and Galetto, 2002).The association found here between flower size and total nectar volume secreted in Ipomoea suggests that structural constraints may play a major role in conserving nectar traits, at least in volume.
Schondube and del Rio (2002) studied the evolution and the correlation between the form of bill birds, the form of corolla, the nectar collection, and its importance in the pollination Ipomoea for Diglossa.The authors observed experimental evidence of a trade-off associated with the evolution of a morphological novelty.Moreover, they indicate that a slight hook might have provided ancestral flower piercers with increased efficiency to pierce and extract nectar from hummingbird-pollinated flowers with sympetalous tubular corollas.Subsequent increases in hook length would have provided flower piercers further access to a diverse range of floral nectar sources unavailable to legitimate, non-robbing, floral visitors.However, a longer hook that allows more effective robbing entails a cost: flower piercers with longer hooks are less efficient frugivores.The differences in hook length among flower piercers with its concomitant trade-off and contrasting diets are also associated with broad interspecific differences in aggressive behaviour and habitat use (Isler and Isler, 1999), and presumably have enabled flower piercer species with and without hooked bills to coexist with each other and with hummingbirds at several Andean locations (Moynihan, 1979;Snow and Snow, 1980).Durbin et al. (2003) used the flower color of Ipomoea as a model for an analysis of flowers evolution and adaptation in relation to mutations in regulation genes expression.Changes in regulatory genes, on the other hand, often result in novel patterns of pigmentation that can influence pollinator behavior or even attract other types of pollinators.For instance, if natural pollinators decreased in the environment of a species, a change in pigment patterns could attract other types of Acta Scientiarum.Animal Sciences Maringá, v. 27, no. 1, p. 137-143, Jan./March, 2005 pollinators ensuring pollination, a presumably beneficial event.Also, a change in pigment patterns could lead to genetic isolation due to a change in pollinator preference.Genetic isolation could ultimately lead to the evolution of a new species.In addition to the large impact changes in expression patterns can have, there are many more ways in which mutations in regulation can occur when many different types of genes involved in regulation and the seemingly redundant tissue specific regulatory genes are considered.Small changes in regulation of the flavonoid pathway can effect large changes in phenotype and adaptive success.
Although the molecular basis for the changes is not known, the regulation of expression of genes of the flavonoid pathway in the species is observed in this study.It appears that changes in regulation of gene expression are the main driving force behind the adaptive and phenotypic evolution of flower color in Ipomoea.
Ipomoea is a weed that presents wide diversity in ways for its reproduction and competition with other weed.However, some aspects of the pollination and pollinators need to be understood for the development of control programs of these plants.

Figure 3 .
Figure 3. Viability of pollen grains of Ipomoea batata (A) and Ipomoea quamoclit (B) during the day.

Table 1 .
Medium height (mm), standard deviation and number of flower of Ipomoea acuminata analyzed by morphometry.

Table 2 .
Medium height (mm), standard deviation and number of flower of Ipomoea batata analyzed by morphometry.

Table 3 .
Viability of pollen grains during the day in Ipomoea batata.

Table 4 .
Table4only the medium height of the Filament 5 at 8:00 a.m. was higher than medium height of the style in that time.Medium height (mm), standard deviation and number of flower of Ipomoea cairica analyzed by morphometry in three times during the day.

Table 5 .
Averages, standard deviation and number of flower of Ipomoea quamoclit analyzed by morphometry in two times during the day.

Table 6 .
Viability of pollen grains during the day in Ipomoea quamoclit.