THE EFFECT OF ACHENE HETEROMORPHISM ON PROGENY TRAITS IN THE SHAGGY SOLDIER [ Galinsoga ciliata ( RAFIN ) S . F . BLAKE ]

The shaggy soldier [Galinsoga ciliata (Rafin) S. F. Blake], family Asteraceae] is an invasive species that poses a growing threat to crop production. This annual plant produces heteromorphic achenes in a capitulum type inflorescence. The objective of this study was to compare selected morphological and phenological parameters and the success of generative reproduction in plants developed from peripheral and central achenes of the capitulum. The somatic variability of G. ciliata diaspores contributed to differences in the growth rates, development and fertility of the resulting populations. The progeny of central diaspores developed at a slower rate than the individuals derived from peripheral achenes, but at the end of their life cycle, the offspring of dimorphic achenes formed homogenous groups as regards height values. On average, the initial phenophases of G. ciliata plants derived from central achenes began one day later, and they entered the flowering stage eight days later than the individuals developed from peripheral seeds. At the initial growth stage (experimental day 65 to 83), the progeny of central achenes produced fewer capitula. On day 133, the individual fertility of the plants derived from central diaspores was 10% higher on average in comparison with the offspring of peripheral achenes.


INTRODUCTION
Heteromorphism promotes the development of various ecological strategies of evolutionary significance.The production of seeds and fruits with different dispersal capacity, dormancy patterns and germination requirements is a specific feature of that strategy which enables species to survive under variable and unpredictable environmental conditions (I m b e r t , 2002; M a t i l l a et al. 2005; V e n a b l e , 1985).
In plants of the family Asteraceae, heteromorphism is manifested by the formation of two types of achenes in the inflorescence (capitulum): peripheral achenes in the outer whorl and central achenes situated above (R o c h a , 1996; V e n a b l e and L e v i n , 1985a).In many species, achenes differ with regard to their size, shape, mass, depth of dormancy, germination and dispersion ability (B a s k i n and B a s k i n , 1998; C o r k i d i et al. 1991;Flint and Palmblad, 1978 In some cases, the morphological differentiation of achenes is related to dispersion polymorphism, but it does not result in germination variability.Weakly dispersed achenes have also been found to germinate more rapidly and fully than widely dispersed diaspores (C h m i e l e w s k i , 1999; E l l n e r , 1986, I m b e r t et al. 1996, P i t e l k a et al. 1983).
Whereas the dispersion ability, dormancy and germination of heteromorphic Asteraceae has been thoroughly researched, the progeny of heteromorphic diaspores remains poorly documented.In selected heteromorphic species, seed size affects the size and viability of seedlings, thus contributing to their competitive advantage and reproductive output at later stages of life (I m b e r t , 2002; R a i and T r i p a t h i , 1987; V e n a b l e and L e v i n , 1985b; V e n a b l e et al. 1987).In selected annual plants of the family Asteraceae, achene mass is positively correlated with seed embryo size.In other species, the higher mass of  . 1997; 1996).
The objective of this study was to examine the progeny traits of the shaggy soldier, Galinsoga ciliata (Rafin) S. F. Blake (family Asteraceae), derived from heteromorphic diaspores, and to compare selected morphological and phenological parameters and the success of generative reproduction in plants developed from peripheral and central achenes.

Species
The shaggy soldier [Galinsoga ciliata (Rafin) S. F. Blake], a popular weed of root crops, grain crops and stubble fields, is an invasive species that easily colonizes new territories.It is a widely propagating and an increasingly aggressive species that poses a growing threat to crop production in Poland (K o r n i a k , 1997; 1992; T r z c i ń s k a -T a c i k et al. 2009).

Achenes
The experimental materials comprised mature achenes of G. ciliata collected on 20 September 2004 from a weed population in carrots grown in the Experimental Garden of the University of Warmia and Mazury in Olsztyn (53°78˚N latitude and 20°49˚E longitude), on heavy loamy sand soil deposited on a light loamy layer, of quality class IIIa.On the next day after harvest, the achenes were divided into two groups based on their position in the inflorescence.Two distinct types of achenes are produced on the same receptacle.One type, formed from central florets, is characterized by a pappus-scales aristate; the other type, formed from peripheral florets, has a strongly reduced pappus (K u l p a , 1988).

Experiment
The experiment was carried out in the greenhouse of the Experimental Garden of the University of Warmia and Mazury in Olsztyn.G. ciliata achenes were sown on 3 December 2004.10 seedlings per achene type were planted in pots filled with substrate (50% sterile soil, 50% compost).Greenhouse temperature was maintained at 22-24°C during the day and 15-18°C at night.The beginning of selected phenophases was determined from the sowing date.Plant height was measured on day 31, 41, 51, 65 and 133 after emergence.The number of capitula and seeds per capitulum was determined at various stages of development.The collected data were used to estimate individual fertility.The experiment was terminated 133 days after emergence.

RESULTS
G. ciliata plants derived from central and peripheral achenes were characterized by various growth rates.The plants from central achenes developed at a slower rate than the progeny of peripheral achenes.On observation day 65, their average height was lower by approximately 6 cm, and on day 133, the differences in height were leveled out between the studied morph groups (Table 1, Figs 1, 2, 3).
The initial phenophases in plants derived from central achenes commenced one day later in comparison with the individuals developed from peripheral achenes.Significant differences were noted in respect of the time of first flowering, and the progeny of central achenes began to flower eight days later than the individuals derived from peripheral achenes (Table 2).The above resulted in lower fertility values of the offspring of central achenes (number of capitula per plant) on day 65 and 83.On day 83, the progeny of central achenes produced approximately 50 fewer capitula in comparison with the plants derived from peripheral achenes.Between days 83 and 133, a visible increase in the reproductive effort of plants from central achenes was observed.On day 133, they produced approximately 28 more capitula, and each capitulum contained more achenes than in the progeny of peripheral achenes.Individual fertility values were higher in the offspring of central achenes by approximately 10% on the last day of the experiment (Table 1).

DISCUSSION
The effect of achene heteromorphism on the growth and reproduction of Asteraceae plants has been scarcely investigated.The existing studies indicate that the progeny traits of heteromorphic achenes differ subject to species and environmental conditions (  In this experiment, the progeny of the shaggy soldier derived from peripheral achenes was marked by faster growth rates until day 65.Between days 65 and 133, the growth of individuals derived from central diaspores was accelerated.On the last day of the experiment, G. ciliata plants developed from peripheral achenes were characterized by higher average height in comparison with the progeny of central achenes, but the distribution of values leveled out the differences between the offspring of different morph types.regardless of achene heteromorphism (Table 1, Figs 1,  2, 3).As regards Crepis aspera, seed morphology did not affect plant growth or height values in successive days of the experiment.In Hedypnois cretica populations, no differences were noted in the initial phenophases, and the height of individuals produced by dimorphic fruit was differentiated at successive growth stages (E l -K e b l a w y , 2003).

Mature individuals formed homogenous populations
The somatic variability of G. ciliata diaspores contributed to significant differences in plant development.The individuals produced by central achenes were marked by slower growth rates and delayed onset of flowering, but their reproductive effort was intensified at later stages between days 83 and 133.During this period, the capitula of plants derived from central diaspores produced more achenes than the progeny of peripheral diaspores.The ultimate individual fertility of central plants was approximately 10% higher in comparison with peripheral plants (Table 1, 2).G. parviflora individuals developed from peripheral achenes were marked by higher fertility values (number of capitula and number of seeds per plant) than the progeny of central achenes (at low and average NPK concentrations) (R a i and T r i p a t h i , 1987).H. cretica plants derived from peripheral diaspores produced a higher number of inflorescences than individuals developed from central achenes (E l -K e b l a w y , 2003).The progeny of C. aspera and C. sancta grown from heteromorphic achenes produced similar numbers of capitula (E l K e b l a w y , 2003, I m b e r t et al. 1996).In G. ciliata, the morphological and phenological differences between the progeny of various morph types were manifested at different stages of life.According to E l -K e b l a w y (2003), dimorphic features continue to affect individual traits at every developmental phase.

CONCLUSIONS
1.The somatic variability of G. ciliata diaspores contributed to differences in the growth rates, development and fertility of the resulting populations.
The morphological and phenological differences between the progeny of various morph types were manifested at different stages of life 2. Differences were noted in the growth rates of G. ciliata plants derived from central and peripheral achenes.The progeny of central diaspores developed at a slower rate than the individuals derived from peripheral achenes, but at the end of their life cycle, the offspring of dimorphic achenes formed homogenous groups as regards height values.3. On average, the initial phenophases of G. ciliata plants derived from central achenes began one day later, and they entered the flowering stage eight days later than the offspring of peripheral diaspores.
; I m b e r t , 2002; I m b e r t et al. 1996; R o c h a , 1996; T a n o w i t z et al. 1987).Selected representatives of Asteraceae adopt the strategy of weak dispersion and delayed germination of weakly dispersed peripheral achenes as well the strategy of strong dispersion, faster and fuller germination of widely dispersed central achenes (R o c h a , 1996; T a n o w i t z et al. 1987, V e n a b l e et al. 1987).The above strategies are not obligatory in all species.
peripheral achenes is attributed to the specific pericarp structure which plays an important role in germination, in particular water absorption by embryonic tissue and gaseous exchange (E l -K e b l a w y , 2003; I m b e r t , 2002; I m b e r t et al. 1997; R u i z D e C l a v i j o and J i m é n e z , 1998).The effect of seed heteromorphy on growth, development and generative reproduction was investigated in very few species (E l K e bl a w y , 2003; I m b e r t et al I m b e r t et al. 1996, B e n e k e et al. 1993, V e na b l e and L e v i n , 1985b

Fig. 1 .
Fig. 1.The height [cm] of Galinsoga ciliata plants derived from peripheral and central achenes on experimental day 51 ). Research results suggest that heteromorphic G. ciliata diaspores produce progeny marked by different growth patterns over time.On average, the initial phenophases of G. ciliata plants derived from central achenes began one day later in comparison with the progeny of peripheral achenes (Table2).According to S y m o n i d e s(1977), under the fluctuating conditions of natural habitats, this slight reduction could be sufficient to lead to great differences in survival.Significant differences were noted as regards first flowering dates.The plants developed from (R a i and T r i p a t h i , 1987).In dimorphic populations of Crepis sancta, the plants derived from peripheral diaspores were characterized by higher viability, larger embryos and seedlings in comparison with the progeny of central achenes.Despite the above, pheno-logical observations of C. sancta did not validate the significance of achene morphology on plant growth (I m b e r t et al. 1996).