Biology of weeds

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Weed species

Some info

  • Weed: A plant that is successful in colonizing disturbed, but potentially productive sites and at maintaining their abundance under conditions of repeated disturbances Mohler, C. 2001. Ecological Management of Agricultural Weeds
  • Disturbance: A discrete event that disrupts ecosystem, community or population structure. A disturbance changes resources, substrate availability or the physical environment Pickett and White, 1985
  • What makes weed a weed: (Holm, 1978):
    • Long seed life in the soil
    • Quick emergence
    • Rapid early growth
    • No special environmental requirements for germination
    • Ability to survive and prosper under disturbed conditions

Some weeds

Species Common name Stress Comments Reference
Amaranthus spinosus Spiny amaranth Drought C4 plant, so expected to have a competetive advantage over C3 plants such as rice under drought. Chauhan, 2013
Leptochloa chinensis Chinese sprangletop Drought C4 plant, so expected to have a competetive advantage over C3 plants such as rice under drought. Chauhan, 2013
Centaurea diffusa Diffuse knapweed Nitrogen limitation Best competitor (in a study of four focal native species) under low and high nitrogen conditions. Suding et al, 2004
Centaurea diffusa Diffuse knapweed Phosphorus limitation C. diffusa lost its competitive advantage Suding et al, 2004
Ruellia tweediana Mexican petunia (Acanthaceae) Multiple growth conditions RT showed competitive advantage over RC across several conditions. Wilson, 2004
Lonicera japonica Honeysuckle Climbing support Comparison with L. sempervirens in this study and other studies showed increased CO2 accumulation, higher photosynthetic rates, better defense response Schweitzer and Larson, 1999
Centaurea solsitialis XX Our results suggest that the invasiveness of C. solstitialis arises, in part, from its combined ability to persist in competition with annual grasses and its plastic growth and reproductive responses to open, disturbed habitat patches Gerlach and Rice, 2003
Fraxinus uhdei Tropical ash Gleason and Ares, 2004
  • NDSU Ag: Drought tolerant weeds such as kochia, Russian thistle, and perennial weeds are more troublesome with dry conditions than weeds such as wild mustard, wild buckwheat, or wild oats, which tend to be more serious problems with good growing conditions. Weed emergence also may be delayed or erratic in dry years. Weeds that normally would emerge early in the season and be controlled prior to planting may not emerge until later. Therefore, multiple flushes of weeds may occur as rainfall is received throughout the season.

Weeds with sequenced genomes

Notes

Rathore 2013

  • The effect of high and low temperatures was studied in two invasive weed species, Eupatorium adenophorum Spreng and Eupatorium odoratum L. [42], to establish the relationship between the antioxidant defense mechanism and temperature tolerance in these weeds. In E. adenophorum, a coordinated increase in activities of antioxidant enzymes was found to be effective in protecting the plant from the accumulation of reactive oxygen species (ROS) at low temperature; however, no such protection was observed during heat treatment. In contrast, in E. odoratum, a reverse trend was observed in terms of membrane damage and a coordinated increase in antioxidant enzymes was observed in plants exposed to heat stress, but such response could not be achieved in plants exposed to cold stress. This indicates that E. odoratum plants have a higher capacity for scavenging oxygen radicals under heat stress, while E. adenophorum plants have a higher capacity under cold stress. **Differential regulation of antioxidant defense mechanisms may be one of the potential strategies for high- or low-temperature tolerance between the two weed species, and this differential ability may be utilized for crop improvement for heat and cold tolerance by the intervention of biotechnology.**
  • Maize is a C4 plant that requires warm environments at either end of the growing season. Low temperature at the beginning or at the end of the growing season limits the growing period, thus limiting yield also. A breakthrough has been made by researchers to get rid of the intolerance to low temperature of maize plants, which eventually may extend the length of the growing season and lead to better yields [43]. Miscanthus � giganteus, a C4 grass related to maize, exceptionally productive in cold climates, provides clues for the genetic engineering of maize for low-temperature tolerance. To solve the puzzle of cold tolerance of Miscanthus �giganteus, scientists focused on the enzyme pyruvate phosphate dikinase (PPDK), which is made up of two subunits. The expression profile of the gene coding for PPDK revealed that when leaves of maize were placed in the cold, PPDK slowly disappeared with a concomitant decline in the rate of photosynthesis. In contrast, when Miscanthus leaves were exposed to cold they produced PPDK at a greater rate, enabling leaves to maintain photosynthesis in the cold conditions [43]. The finding suggests that engineering of maize plants to synthesize more PPDK during a cold climate may allow this crop to be cultivated for longer periods in its current locations and even in colder climates, and thus may boost the production of maize.
  • In Prosopis chilensis and soybean, ubiquitin and conjugated ubiquitin synthesis during the first 30 min of exposure to heat stress was observed as an important mechanism of heat tolerance [51]. In Chenopodium murale, leaf protein extracts from thylakoid and stromal fractions exposed to heat stress revealed the Cu/Zn-SOD of the stromal fraction to be more heat tolerant than that of the thylakoid fraction and this was responsible for chloroplast stability under heat stress [52]. The antioxidant defense mechanism is a part of heat stress adaptation and its strength is correlated with acquiring thermotolerance [53]. Thermotolerance can also be induced by gradually increasing temperature to its lethal dose, as would have occurred naturally [54], and such an adaptation would involve a number of pathways. Using Arabidopsis mutants it was shown that apart from HSPs (HSP32 and HSP101), ABA, ROS, and salicylic acid pathways are also involved in the acquisition of thermotolerance [55,56]. The mechanisms that protect cells from heat stress are the key factors in acquiring thermotolerance [47]. Recently, Khanna-Chopra et al. [57] exposed the leaf and inflorescence of Chenopodium album to heat stress (5–100 �C) for 30 min. Antioxidant enzymes (SOD and ascorbate peroxidase (APX)) showed activity even after boiling in both chloroplasts and mitochondria of the leaf and inflorescence; however, SOD was found to be more stable than APX in both organelles of both the tissues. These heat-stable isozymes of SOD and APX may contribute to heat tolerance in C. album, and can be good genetic material for engineering crop plants for high temperature tolerance.
  • Polyamines are nitrogenous secondary metabolites that have been reported to be involved in a variety of stress responses in plants. Modulation of the polyamine biosynthetic pathway in transgenic rice conferred tolerance to drought stress [59]. It has been difficult to establish if high putrescine is the cause of stress-induced injury or a protective response resulting from stress. In another study, transgenic rice plants expressing the adc (arginine decarboxylase) gene from Datura stramonium produced much higher levels of putrescine under stress, promoting spermidine and spermine synthesis, and ultimately protecting the plants from drought [59]. Results suggest that manipulation of polyamine biosynthesis in plants can produce drought-tolerant genotypes. In this study, the noteworthy point is that the source of the adc gene is D. stramonium – a common weed, which itself can tolerate a high degree of drought.
  • In the Thar desert of India, weed species that experience a number of stress factors like high temperature and prolonged drought conditions during summer and extreme low temperature in winter can be a potential source for crop improvement, especially abiotic stress tolerance. Oropetium thomaeum is abundant in the area near Jodhpur and sometimes it completely dominates the ground cover along with only some scattered vegetation [60]. Metabolic characterization of this plant suggests that it accumulates a high content of sucrose, raffinose, and stachyose, and a low content of monosaccharides in leaf tissues under dehydration. In addition, two prominent proteins related to water stress, namely the LEA (late embryogenesis abundant) dehydrin and aldose reductase, are also present in the dehydrated tissues [61]. The induction pattern of these proteins in dehydration-sensitive maize and dehydration-tolerant O. thomaeum when subjected to dehydration indicates that aldose reductase protein was expressed in desiccated leaves of O. thomaeum, but never in leaves maize. From the results, it can be inferred that the presence of aldose reductase protein in the leaves can be considered as a marker for desiccation tolerance, at least in monocotyledonous plants, and O. thomaeum can be a suitable source for molecular manipulation of crop plants for drought tolerance. Physalis minima, another common weed, possesses a high degree of tolerance to water deficit with a unique property of fast recovery from an almost permanent wilting point. In an ongoing pot experiment at the authors’ institute, P. minima showed tolerance up to 13 days of water deficit in vermiculite growing media and recovered within 6 h without showing any injury symptoms [62]. Phalaris aquatica is a deep-rooted, productive perennial grass that possesses a high degree of drought tolerance and hence may be a good source of genes for genetic engineering of cereals for improvement of drought tolerance [63].
  • To identify the major weeds and their adaptive potential in the saline ecosystem, a survey was conducted in Pokkali rice cultivation areas [66]. Diplachne fusca, Echinochloa crusgalli, Panicum repens, Fimbristylis miliacea, Eleocharis dulcis, Cyperus difformis, Eichhornia crassipes, Lemna polyrrhiza, Spirodela polyrhiza, Pistia stratiotes, Monochoria vaginalis, Alternanthera sessilis, Nymphaea nouchali, Sphenoclea zeylanica, Ludwigia parviflora, Sphaeranthus africanus, Salvinia molesta, Azolla pinnata, and Ceratopteris thalictroides were major weed species found in Pokkali areas. Out of these, D. fusca was the most dominant and abundant weed species, occurring in approximately 85% of the sites surveyed, followed by E. crusgalli. Analysis of D. fusca and E. crusgalli revealed the presence of Kranz anatomy, a typical characteristic of C4 plants, and robust and efficient growth. The presence of microhairs on the leaves of D. fusca that function as salt glands and secrete salt on the leaf surfaces is another adaptive feature. From the above results, it can be inferred that Pokkali can be a good source of genetic material for rice improvement against salt stress, while other weeds species can be used potentially for improvement of salt tolerance in other related crops.
  • In a comparative study involving rice and E. crusgalli, growth inhibition and decrease in relative water content under salt stress was more severe in rice than in E. crusgalli; however, accumulation of proline in leaves was significantly higher in salt-stressed E. crusgalli than in rice, indicating the better osmotic adjustment potential of E. crusgalli by means of enhanced proline synthesis [69]. In addition, salt stress also affected polyamine metabolism of both plant species; however, the response of each plant to salt stress was somewhat different, especially in the leaves. Putrescine and spermidine contents in leaves were high in non-stressed plants in rice, although rather lower in E. crusgalli in response to NaCl concentrations. Together, the results indicate that an increase in proline and changes in polyamines relate to the salt tolerance of E. crusgalli.
  • In another study [70], the comparative performance of rice and E. crusgalli was examined, and it was found that accumulation of salicylic acid occurred in salt-stressed rice seedlings. Furthermore, it was suggested by the authors that accumulation of salicylic acid might potentiate oxidative injury in rice seedlings since inhibition of salicylic acid synthesis alleviated growth inhibition under high salinity. On the contrary, in E. crusgalli seedlings exposed to high salinity, no increase in salicylic acid content was evident. In confirmation of the above contention, it was observed that foliar application of salicylic acid led to growth inhibition of E. crusgalli seedlings under salt stress concomitantly with a striking reduction of the efficiency of Photosystem II. Catalase and SOD activities in E. crusgalli seedlings were induced by the salt treatment, which further provide protection against salt-induced ROS. However, salicylic acid pretreatment suppressed such an induction of catalase activity, but promoted SOD activity that, in turn, led to the build-up of leaf hydrogen peroxide. It was advocated that accumulation of cellular salicylic acid facilitates the generation of H2O2 in rice through the suppression of catalase activity and concomitant promotion of SOD activity. On the other hand, E. crusgalli seedlings have a mechanism to check the accumulation of salicylic acid and hence prevent build-up of hydrogen peroxide. The results together indicate the inherent adaptive potential of E. crusgalli under salt stress that can be explored in terms of genetic material for salt tolerance engineering.
  • Many other examples in the book

Others

  • Wiese and Vandiver (95) compared the growth and competitive ability of sorghum (Sorghum vulgare Pers., C4), corn (Zea mays L., C4), and eight weed species at three levels of soil moisture in a greenhouse. Corn produced the most biomass, regardless of moisture level. Among the weeds, those species normally growing in humid regions or in irrigated crops (cocklebur (Xanthium strumarium L., C3), barnyardgrass (Echinochloa crus-galli (L.) Beauv., C4), and crabgrass(Digitaria sanguinalis(L.) Scop., C4) were most competitive under moist conditions. Weeds typical of dry habitats(kochia (Kochia scoparia (L.) Schrad., C4) and Russian thistle (Salsola iberica Sennen&Pau,C4)) were more competitive under dry conditions and grew poorly in competition at the high moisture level.
  • Many weeds appear to be "waterwasters" in that their stomata are less sensitive to declining leaf water potential than those of the crops with which they compete. If this characteristics combined with a more extensive root system and/or better physiological tolerance of drought,the weed may quickly exhaust the water supply available to the crop(29,71, 83).This characteristic of excessive wateruse by weeds may be advantageous in the context of weed/crop competition, provided the weed can survive and reproduce under the resultant soil water deficit.
  • Chauhan, 2013: Growers in many parts of Asia are shifting their rice production systems from traditional transplanting of seedlings to direct-seeded systems in response to water and labor scarcities. Weeds, however, are the most important biological constraint in direct-seeded rice production systems [7] as weeds and rice emerge simultaneously and there is no standing water at the time of crop emergence. In water-limited fields, weeds may reduce the available water to crops by competition and cause water stress in crops [8]. Amaranthus spinosus L. (spiny amaranth, a C4 broadleaf species) and Leptochloa chinensis (L.) Nees (Chinese sprangletop, a C4 grass species) are amongst the dominant weed species occurring in direct-seeded rice (C3 species) systems [9-13]. A. spinosus was reported to occur in 15 countries in dry-seeded rice systems [14]. It is a prolific seed producer and the spines
  • Chauhan, 2013: Rice died at 25% and 12.5% field water capacity but weeds survived. In previous studies, rice grew best at 120% to 160% of FC and rice was more competitive than weeds with sufficient moisture, but weeds were more competitive than rice with water stress [23,24]. In water-limited environments, weeds may have higher leaf water potential than rice, suggesting that a limited amount of water in soil would benefit weeds more than rice [25]. In another study, too, A. spinosus had higher water potential values than the rice in both well-watered and water-stress treatments [13]. Such information, however, was not found for L. chinensis.
  • Chauhan, 2013: There is a need to breed improved rice cultivars tolerant of water stress. Weed infestation in water-limited environments may decrease rice yield in addition to the effect of water stress on the rice crop. Therefore, it is important to control weeds in the early stages of crop growth and preserve moisture for the crops. Post-emergence herbicide efficacy may be less in water-stressed conditions, mainly because of less herbicide absorption. An earlier study showed that the doses of herbicides to effectively control Commelina benghalensis L. (Bengal dayflower) increased upto 250 times at 25% of FC compared with herbicide application at 100% of FC [31]. Weed plants may develop a thicker leaf cuticle in water-stressed conditions, and the thick cuticle may reduce herbicide entry into the leaf [8,32]. Therefore, any weed plants escaping after herbicide application in water-stressed fields should be removed to prevent future infestation.
  • Entz, 2005: Many weeds exhibited similar or greater responses in shoot and root biomass to increasing amounts of soil N, compared with wheat or canola. Our findings support the concept that many common agricultural weeds have adapted to relatively high soil N conditions often present in crop production systems. The high responsiveness of many weed species to N may be a weakness to be exploited through development of fertilizer management methods that enhance crop competitiveness with weeds.
  • Stanton, 2000: For example, crop yield losses due to barnyardgrass competition have been reported as 8 to 82% in corn (Spitters et al., 1989) and 30 to 45% in cotton (Kempen, 1984)
  • Richards, 2006: We suggest that a successful invader may benefit from plasticity as either (1) a Jack-of-all-trades, better able to maintain fitness in unfavourable environments; (2) a Master-of-some, better able to increase fitness in favourable environments; or (3) a Jack-and-master that combines some level of both abilities.
  • Richards, 2006: Phenotypic plasticity in plant invasions. In particular, many studies argue that plasticity enhances ecological niche breadth because plastic responses allow organisms to express advantageous phenotypes in a broader range of environments (Bradshaw 1965; Van Valen 1965; Whitlock 1996; Sultan et al. 1998a,b; Donohue et al. 2001; Sultan 2001; Richards et al. 2005). Recent studies also suggest that the evolution of plasticity in response to a set of environments may be beneficial in novel sites after colonization or migration (Agrawal 2001; Donohue et al. 2001, 2005; Etterson 2004; Yeh & Price 2004).
  • Richards, 2006: Whether one is interested in cross-species comparisons or microevolution, there are two primary scenarios which describe how a different reaction norm might contribute to invasion success: (1) a Jack-of-all-trades situation, where through the plasticity of morphological or physiological traits, the invader is better able to maintain fitness in a variety of environments; (2) a Master-of-some situation, in which the plasticity of morphological or physiological traits allows the invader to take advantage of favourable environments; in addition, an invader might be (3) a Jack-and master that combines some of both of these abilities.
  • Richards, 2006: Because phenotypic plasticity is a property of specific traits in specific environments, it is incorrect to think of an organism or genotype as a whole as being more or less "plastic" than others. A given genotype may be plastic for a certain trait in a certain set of environments, but not plastic for other traits in the same set of environments, or for the same trait in a different set of environments (Bradshaw 1965; Sultan 1995; Pigliucci 2001). Plasticity of morphological and physiological traits is unlikely to have any effect on invasiveness unless that plasticity contributes to fitness (Fig. 1).

* Richards, 2006: ...in Herbert Baker’s seminal paper on the characteristics of weeds (Baker 1965)...he recognized that there are two aspects to the response of fitness traits to environmental variation that might contribute to the success of an invader: (1) the ability to maintain fitness across a broad range of environments, a characteristic clearly related to the concepts of a general purpose genotype (Baker 1965) and of fitness homeostasis (Hoffmann & Parsons 1991; Rejma ´nek 2000); and (2) the ability to increase fitness in favourable environments (see for example, Sultan 2001). The first characteristic stresses the importance of robustness under unfavourable conditions, the second stresses opportunism under favourable conditions.

  • Wilson, 2004: Ruellia tweediana (invasive) had greatest dry weight increase in wet conditions vs native Ruellia caroliniensis, net CO2 accumulation under both wet/dry conditions was higher, shoot N2 and P use efficiencies were higher. RT produced more seeds over the season than RC.
  • Gleason and Ares, 2004: Seedlings of both species were grown in a greenhouse in three light treatments: 100% photosynthetic photon flux (PPF); 18% PPF; and 2% PPF inside the greenhouse. Light compensation point, maximum CO2 assimilation rate and dark respiration rate of seedlings differed significantly among light treatments, but were similar between species. A defoliation experiment indicated that tropical ash was better able to survive defoliation than koa, especially under high-light conditions. Tropical ash seedlings allocated more carbon (C) and nitrogen (N) to storage per unit PPF than koa seedlings. Total nonstructural carbohydrates were positively correlated with plant survival in both species. The patterns of C and N allocation associated with tropical ash seedlings favor their survival in high light, under intense herbivory and on sites where N availability is seasonal or highly variable. Variation in carbohydrate storage between koa and tropical ash greatly exceeded variation in photosynthetic performance at the leaf level.
  • Gressel, XX (Book - Molecular Biology of Weed Control): Herbicide resistance genes for ALS, Dinitroaniline, Atrazine that evolved in weedy populations have now been bred into crop species, providing them tolerance to those herbicides. Another example is the attempted transfer of N-glycosyltransferase from peanut that inactivates pyridate to crops.
  • Book - Abiotic stress adaptations in plants (pg21): Some of the worst weeds are exceedingly diverse and seem to be able to quickly adapt to many changes in agricultural environment as well as herbicides...The capacity to possess mutators might be an inherent property of the most adaptable species. ..Lolium rigidum, L. perenne, L. multiflorum complex of pasture grasses and weeds have evolved resistance to a multitude of environmental stresses and herbicides at an astounding rate throughout the world (Gressel 2002; Preston 2003; Neve and Powles 2005; Owen 2007; Heap 2008). Why not known.
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