Traits of Weed Archetypes
Black nightshade, Solanum nigrum
S. nigrum is reported as
a weed of over 37 crops in 61 countries around the world. It is a common weed of
many fruits, vegetables, crops, waste area, and open forest. It is a native of
Europe. It is also an alternate host of some important fungi, nematode, and
virus diseases (Holm et al. 1991).
There is a taxonomic confusion surrounding S. nigrum and its component species (Edmonds & Chweya 1997), presumably because of the historical factors, phenotypic plasticity, genetic variation, the existence of a polyploid series, and the possibilities of interspecific hybridization (Edmonds, 1977). Therefore, the information about this species has to be interpreted with caution.
The section Solanum, centering around S. nigrum L., is one of the largest and most variable species groups of the genus. Species belonging to this section are distributed from temperate to tropical regions, and from sea level to altitudes over 3500 meters. Though this species group is often referred to as the Solanum nigrum complex, the section is composed of a large number of morphogenetically distinct taxa, which show their greatest diversity (Edmonds & Chweya 1997). The majority of the diagnostic characters, which have been used by some authors to identify the species belonging to the section Solanum, are extremely variable as well as some species are more variable morphologically within this section (Edmonds, 1986).
to Edmonds & Chweya (1997)
S. nigrum L.
has two subspecies:
S. nigrum L. subsp. nigrum,
S. nigrum L. subsp. schultesii
Chromosome no. (2n=72)
The key to differentiate between two subspecies:
S. nigrum subsp. nigrum;
Plants subglabrous to pubescent usually with appressed, eglandular-headed
S. nigrum subsp. schultesii;
Plants villous, usually with patent, glandular-headed multicellular hairs
S. nigrum is one of the
worst world’s weeds (Holm et al., 1991) and it cause not only crop yield
losses through competition for recourses, but also cause reduction of crop
quality by contaminating crops such as peas, beans and soybean (Edmonds & Chweya, 1997; Defelice, 2003).
It also host insects, nematodes, and disease organism that attack crops (Ogg
& Rogers, 1989). Members of Solanaceae contain a toxic glycoalkaloid called
solanine. The amount of this toxin varies with the species, environment, part of
the plant, and stage of growth (Defelice, 2003), genetic races, soil factors,
management practice, and climate conditions (Ogg & Rogers, 1989). The
highest concentrations of solanine in S. nigrum are in the immature
fruits (Defelice, 2003). The unripe green berries may inadvertently pick up and
mix with crop i.e. peas. The allelopathic inhibitory effect of extracts from S.
nigrum on chickpea seed germination has been noted (Kadioglu et al., 2005).
S. nigrum is considered as a medicinal plant, source of food, indigenous plant genetic resource in many countries (Ogg & Rogers, 1989; Holm et al. 1991; Agong, 1993; Edmonds & Chweya, 1997; Defelice, 2003). It’s also used as the painkiller (Zubida et al., 2004). An isolated glycoprotein from S. nigrum has been identified as a natural anti-cancer agent (Lim, 2005). Zakaria et al., (2006) demonstrated that the lipid-soluble extract of S. nigrum leaves possessed antinociceptive, anti-inflammatory and anti-pyretic properties.
Solanum nigrum is mainly
a weed of moist environment, and thrives in areas of low rainfall only where the
land is under irrigation. It is best adapted to soils of high fertility,
especially those high in nitrogen and phosphorus. It has been naturalized in
both temperate and tropical regions (Holm et al. 1991). This species colonize moist environments, only occurring in areas of low
rainfall when the land is subject to irrigation. However, it is susceptible to
frost (Edmonds & Chweya 1997).
The potential of seed production in S. nigrum vary in a range of 600 to 168000 seeds per plant (Keeley & Thullen, 1983; Holm et al. 1991; Defelice 2003). Each berry contains 15 to 96 bone-coloured seeds (Ogg & Rogers, 1989; Defelice, 2003).
Long survival of dormant seeds enables a plant population to build up a bank of seeds of different ages in the soil (Håkanson 2003). Seeds of S. nigrum can remain viable in the soil for a long time (Ogg & Rogers, 1989; Keeley & Thullen, 1989). Viability of S. nigrum seeds in the soil has been reported from 18 to 39 years depending on soil disturbance. Tillage can decline number of seeds exponentially over years (Ogg & Rogers, 1989; Defelice 2003). However, appreciable numbers of viable seeds survive in the field for 5 years (Roberts & Lockett 1978). Keeley & Thullen (1989) indicated that S. nigrum seed survival in soil appears to be long. Thus, fields should be kept weed-free for more than 5 years to reduce S. nigrum populations to a level that will not reduce cotton yields. Also, S. nigrum seeds remain viable after being eaten by birds and livestock (Roberts & Lockett 1978; Defelice, 2003).
S. nigrum seed dispersal is through contaminated agricultural products or by birds and animals who eat the succulent berries (Roberts & Lockett 1978; Edmonds & Chweya 1997; Defelice, 2003). Also, it has been suggested that migratory birds may have played an important role in spreading seeds of S. nigrum resistant to triazines in Europe (Stankiewicz et al. 2001).
Seed dormancy of S. nigrum has been recognized as non-deep physiological dormancy (Baskin & Baskin, 1998). The breakage of dormancy occurs increasingly in seed stratified in low temperatures up to 15 ºC and a breakpoint is between 15 and 18 C, where phases of dormancy breakage and induction meet as a result of stratification duration (Taab, 2007). In general, freshly harvested S. nigrum seeds have little or no dormancy and germinate within a few weeks of separation from the berry (Keeley & Thullen, 1983; Ogg & Rogers, 1989; Robert and Locket, 1978; Defelice 2003). However, a study on primary seed dormancy of S. nigrum showed differences between populations and date of collection. A substantial germination occurred only in germination condition test in light indicating light requirement for terminating seed dormancy in this species. Also, the light requirements for germination could be decreased by prolonged cold stratification (Taab, 2007). The changes in seed dormancy of S. nigrum follow a seasonal pattern. The cold temperatures during autumn, winter and spring break seed dormancy and warm temperatures during summer cause induction of dormancy in this species, showing characteristics of summer annual behavior (Taab & Andersson, 2007; Roberts and Lockett, 1978).
S. nigrum seeds can
germinate over a very wide period in spring and summer (Defelice, 2003). Both
buried and freshly harvested seeds of S. nigrum cannot germinate at
constant temperatures in the range of 4-30ºC with intermittent exposure to
light, but alternating temperatures cause complete or almost complete
germination (Roberts and Lockett, 1978).
& Van Opstal (1979) showed that an alternating temperature is necessary for
seed germination of S. nigrum, and the germination percentage is also
improved by a cold pre-treatment. Del
Monte & Tarqius (1997) reported that the optimum temperature for germination
of S. nigrum populations is between 20ºC to 30ºC and there are differences
in base temperature for germination between populations from 7.5ºC
to 10ºC. However the S. nigrum seed seems to germinate best at
alternating temperature of 20 to 39 ºC
(Holm et al. 1991).
S. nigrum prone to late germination mainly in late spring (Håkanson 2003). Seedling emergence in S. nigrum begins in early May, continued during June and July, tail off during August and cease in September in U.K. (Roberts and Lockett, 1978). A study by Ogg & Dawson (1984) in USA showed that S. nigrum generally began to emerge during the first 2 weeks of April and emergence generally peaked in mid-April to mid-May and continued until September. Also, shallow tillage at monthly intervals increased the overall its emergence. Keeley & Thullen (1983) stated that S. nigrum seeds begin to emerge in March in California when soil temperature at 5 cm depth reached 17 ºC. Though differences has been observed between populations S. nigrum seedling emergence starts in May and seized in early July in Sweden. Seedling emerged in late spring have enough time to complete their life cycle and induction of seed dormancy during summer inhibits late germination and subsequent plant death in autumn (Taab, 2007). Therefore, the comparatively late emergence contributes to the seriousness of the species as a weed of various vegetable and arable farm crops, since it often take place after contact herbicides have been applied and when the activity of soil-applied treatments has declined (Roberts and Lockett, 1978).
Kremer and Lotz (1998) reported significant differences between triazine resistant and susceptible S. nigrum biotypes in emergence fractions. Resistant seeds showed a higher emergence fraction than susceptible seeds. Solanum nigrum seedlings resistant to triazine herbicides emerged faster and in greater proportion than triazine-susceptible seedlings, because of the interaction between soil temperature and differential minimum germination requirements of seeds between the biotypes (Kremer and Lotz, 1998). S. nigrum seeds seem to emerge from a depth of 2.5 (Keeley & Thullen 1983), 4 (Kremer and Lotz 1998) up to 8 cm (Benvenuti et al., 2001) depending on type of soil.
Black nightshade is sensitive to shading and crop competition and its growth and seed production is severely decreased under shade (Holm et al., 1991). S. nigrum plant that germinated from March through June began flowering 7 to 9 weeks after planting, whereas plant germinating from July through September flowered after 5 to 6 weeks. Plants germinating in October were killed by frost in November. Plant growth was more rapid for plant that germinated from May through July (Keeley & Thullen, 1983). González-Ponce et al. (1996) observed that S. nigrum competes strongly for light, reducing the effective photosynthetically active radiation (PAR) that reaches the lower species, i.e. the pepper with a slower initial growth. McGiffen et al. (1992) reported that height was a major factor in competition between tomato and black nightshade. Black nightshade competition for light and nutrients with tomato was greater when black nightshade was taller than tomato at flower initiation (González-Ponce et al. 1996), which typically occurs when both plants emerge at the same time. S. nigrum plants that emerge late spring in Iran under rather dense crop canopy can produce few berries, which is enough to guarantee future infestation (personal observations).
The leaf margins may vary from entire to sinuate-dentate in different
populations of S. nigrum, while different indumentum types characterize
the different subspecies. S. nigrum also display a range of berry colours
within its subspecies varying from green through purple to black (Edmonds &
Many species in section Solanum exhibit considerable genetic
variation, both florally and vegetatively. This variation may occur in different
populations of the same species, or may characterize different infraspecific
categories of a species. Sometimes, the character may be genetically controlled
in one species, but phenotypically plastic in another. (Edmonds & Chweya
Species belonging to the section Solanum constitute a polyploid
series, with diploid (2n=2x=24), tetraploid (2n=4x=48)
and hexaploid (2n=6x=72) species occurring throughout most of the
geographical range in which the section is found. Octoploid plants (2n=8x=96)
also have been reported (Edmonds & Chweya 1997). S. nigrum is a
hexaploid plant (Edmonds & Chweya 1997;
Sexual fertilization leads to seed production in S. nigrum.
Species belonging to the section Solanum are predominantly
self-pollinating, but out- and crossbreeding can occur as well as natural inter-
and infraspecific hybridizations. Natural hybrids also have been reported at
higher ploidy levels, e.g. infraspecific hybrids of the hexaploid S.nigrum and
interspecific hybridization with other species with different ploidy level
(Edmonds & Chweya 1997).
Some biotypes of S. nigrum have been reported to be resistant to herbicides belong to the Photosystem II inhibitors including atrazine, cyanazine, prometryn, and terbuthylazine and they may be cross-resistant to other herbicides within this group.
Researchers have indicated that resistant S. nigrum is ecologically less fit than normal susceptible one. Triazine resistant weeds often exhibit a lower relative fitness when compared to susceptible biotypes. The most common mutation conferring triazine resistance also causes a reduction in CO2 fixation, quantum yield, and seed and biomass production (weedscience.org, online). Kremer & Kropff (1998) showed that the final total dry matter production and berry production of the triazine-resistant biotype of S. nigrum are lower than those of the susceptible biotype.
It seems that most species in the section Solanum to be capable of hybridization, it is probable that complex population variation would occur where their distributions overlap (Edmonds, 1977). Keeley and Thullen (1983) indicated that S. nigrum planted in May through July produced 20000 to 30000 seeds but only 600 to 8000 seeds per plant when planted in March, April or August. In general, S. nigrum thrive very well and produce large number of seeds when there is enough resource available and no serious crop competition (Holm et al., 1991).
Table of Life History Traits
Plant morphological structure
Seed production plasticity
Soil seed bank formation
Seasonal dormancy cycle
Seed bank formation
Late and extended germination
Vegetative growth plasticity
Herbicide resistant biotype
Seed production plasticity; S. nigrum plants tolerate wide range of habitats, able to start flowering in early stage of growth and potentially capable of producing huge number of seeds under favorable growing conditions and few seeds under unfavorable conditions.
Seed dormancy; S. nigrum seeds go through seasonal dormancy cycle during period of a year. They germinate only when the environmental condition is favorable for germination and its subsequent growth. Therefore, it can build up a seed bank for a long period of time.
Growth habit; although S. nigrum is a late germinating weed, it is able to grow fast and occupy opportunity space between crop stands. It thrives very well when the crop is less competitive or crop canopy is sparse.
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