Variation in damage to cotton affecting larval feeding preference of Spodoptera littoralis

Feeding experiments with larvae of Spodoptera littoralis were performed with leaves from cotton plants subjected to damage and from undamaged plants. In the experiments, four different time intervals (1, 3, 7, and 14 days) after damage induction and two different levels (high and low) of herbivore damage were tested. Seven days after damage induction larvae fed less on the young top leaves from damaged plants for both levels of damage. At the high damage level, the larvae fed less on leaves from the damaged plants after just three days, and this effect still remained 14 days after damage infliction. When mature leaves from the middle of the plant were compared, no difference between treatments was observed.Two plant sizes were tested, small plants with 4–5 true leaves and large plants with 8–10 true leaves. In small plants the induced changes affecting larval feeding were found mainly in the youngest leaf at the top of the plant, while in large plants the induced effects were found in both the youngest and the second youngest leaves.In plants subjected to artificial damage, larvae fed less on top leaves of the damaged plants when compared to leaves from undamaged plants. When leaves from plants that had been artificially damaged were directly compared with leaves from plants damaged by herbivores, larvae fed more on the youngest leaves from artificially damaged plants when the plants were large. In small plants no significant difference was found when comparing artificial and herbivore damage.     

Trap cropping to manage green vegetable bug Nezara viridula (L.) (Heteroptera: Pentatomidae) in sweet corn in New Zealand

Abstract

• 1 The use of trap crops to reduce green vegetable bug (GVB) Nezara viridula (L.) (Heteroptera: Pentatomidae) damage to process sweet corn Zea mays (L.) was investigated in three field experiments.
• 2 In the first season, small plots (2.7 m by 10 m) of white mustard Sinapis alba (L.) with pea Pisum sativum (L.) were sown along a crop border and compared with sweet corn alone.
• 3 In the second season, black mustard Brassica nigra (L.) was sown at two sowing dates (14 days apart) and compared with a sweet corn control, to examine how the maturity of the trap crop affected numbers of GVB trapped.
• 4 A field scale experiment was also conducted to determine the effectiveness of black mustard as a trap crop to protect larger areas of sweet corn from GVB.
• 5 In all three experiments, GVB populations were much higher on the trap crops compared with the sweet corn.
• 6 In both small plot experiments, GVB were contained largely within the trap crop for 2 weeks until the sweet corn was harvested.
• 7 The field scale experiment demonstrated the efficacy of the trap cropping technique to protect larger areas of crop from GVB.
• 8 Percentages of damaged sweet corn cobs in the outside row of fields protected by a trap crop were 0% and 1%, respectively, compared with 11% and 22% in control fields.
• 9 Trap cropping is recommended as an effective strategy to manage this insect. Options for cultivating or spraying the trap crops to reduce bug survival are discussed.

     

Temperature and host-plant effects on development and population growth of Mecinus janthinus (Coleoptera: Curculionidae), a biological control agent for invasive Linaria spp.

Mecinus janthinus Germar is a European stem-mining weevil that has been established in North America as a biological control agent against the invasive European weeds Linaria vulgaris P. Mill. and Linaria dalmatica (L.) P. Mill. (Scrophulariaceae). Establishment success and impact of the weevil have varied widely among sites. We investigated the hypothesis that some of this variation may be due to a lack of sufficient time for M. janthinus to develop to the adult (overwintering) stage in less favorable climates. Development time of M. janthinus was measured in L. vulgaris and L. dalmatica at four constant temperatures, and logistic regression was used to derive a model for the effect of temperature on development. Development rates were simulated using historic climate data for a site in central Alberta (where establishment was marginal on L. vulgaris) and one in southern British Columbia (where outbreaks occurred, resulting in heavy damage to L. dalmatica). The model showed that, on average, the British Columbia site had 50 more days available for the weevil to lay eggs that could reach the adult stage in time for overwintering than did the Alberta site. This may explain the more rapid population buildup at the British Columbia site. This model could be used to predict the climatic suitability of other areas for establishment of M. janthinus. An unexplained result was the very low survival rate of eggs laid in L. dalmatica under the same experimental conditions.     

Temporal dynamics of herbivore‐induced responses in Brassica juncea and their effect on generalist and specialist herbivores

Herbivore feeding may induce an array of responses in plants, and each response may have its own temporal dynamics. Precise timing of these plant responses is vital for them to have optimal effect on the herbivores feeding on the plant. This study measured the temporal dynamics of various systemically induced responses occurring in Brassica juncea (L.) Czern. (Brassicaceae) leaves after insect herbivory in India and The Netherlands. Morphological (trichomes, leaf size) and chemical (glucosinolates, amino acids, sugars) responses were analysed. The effects of systemic responses were assessed using a specialist [Plutella xylostella L. (Lepidoptera: Plutellidae)] and a generalist [Spodoptera litura Fabricius (Lepidoptera: Noctuidae)] herbivore. We tested the hypotheses that morphological responses were slower than chemical responses and that generalist herbivores would be more affected by induced responses than specialists. Glucosinolates and trichomes were found to increase systemically as quickly as 4 and 7 days after herbivore damage, respectively. Amino acids, sugars, and leaf size remained unaffected during this period. The generalist S. litura showed a significant feeding preference for undamaged leaves, whereas the specialist herbivore P. xylostella preferred leaves that were damaged 9 days before. Performance bioassays on generalist S. litura revealed that larvae gained half the weight on leaves from damaged plants as compared to larvae feeding on leaves from undamaged plants. These studies show that although morphological responses are somewhat slower than chemical responses, they also contribute to induced plant resistance in a relatively short time span. We argue that before considering induced responses as resistance factors, their effect should be assessed at various points in time with both generalist and specialist herbivores.     

Effects of heavy metals Cd2+, Pb2+ and Zn2+ on DNA damage of loach Misgurnus anguillicaudatus

The effects of heavy metals Cd²⁺, Pb²⁺ and Zn²⁺ at 0.05, 0.5 and 5.0 mg/L level and their interactions at 0.5 mg/L level on DNA damage in hepatopancreas of loach Misgurnus anguillicaudatus for 1–35 days exposure were examined by single cell gel electrophoresis (SCGE). For each test group, 20 loaches with similar body size (5.17–7.99 g; 11.79–13.21 cm) were selected and kept in aquaria with dechlorinated water at (22±1)°C and fed a commercial diet every 48 h. According to the percentage of damaged DNA with tail and its TL/D (tail length to diameter of nucleus) value, the relationship between DNA damage degree and heavy metal dose and exposure time was determined. Results showed that the percentage of damaged DNA and the TL/D value were increased with the prolonged exposure time. The highest percentage (84.85%) of damaged DNA was shown in 5.0 mg/L Zn²⁺ group after 28 days exposure and the biggest TL/D value (2.50) in all treated groups after 35 days exposure. During the first treated week, the damnification of DNA was mainly recognized as the first level, after that time, the third damaged level was mostly observed and the percentage of damaged DNA was beyond 80%. The joint toxic effects among Cd²⁺, Pb²⁺ or Zn²⁺ revealed much complexity, but it generally displayed that the presence of Cd²⁺ could enhance the genotoxicity of Pb²⁺ or Zn²⁺. In conclusion, the results suggested that there was a significant time-and dose-depended relationship between the heavy metal and DNA damage in hepatopancreas of loach, and SCGE could represent a useful means to evaluate the genotoxicity of environmental contamination on aquatic organisms. __________ Translated from Acta Hydrobiologica Sinica, 2006, 30(4): 399–403 [译自: 水生生物学报]     

Systemic induction of volatile release in cotton: How specific is the signal to herbivory?

Plants attacked by herbivorous insects release chemical signals that attract natural enemies of the herbivores to the damaged plants. Feeding of Spodoptera exigua larvae on the lower leaves of cotton (Gossypium hirsutum L.) for multiple feeding periods of 9–12 h with a 12 h, interval in between when the caterpillars are removed overnight, will induce a systemic release of volatile compounds that is comparable to the volatiles released in response to continuous feeding damage on the lower leaves for several days. The systemic volatile release in response to herbivory can be mimicked by mechanically damaging the lower leaves and applying caterpillar oral secretion to the injured leaves over 4 days. Cotton plants that are only mechanically damaged systemically release significantly less -pinene, myrcene, (Z)-3-hexenyl acetate, (E)--farnesene and (E,E)--farnesene after 4 days compared to plants damaged mechanically with application of caterpillar regurgitant. However, multiple 9–12 h mechanical damage alone induces a significantly higher systemic release of (Z)-3-hexenyl acetate, myrcene, (E)--ocimene, and (E)--farnesene after 4 days compared to undamaged control plants. This indicates that multiple mechanical damage alone cannot mimic completely the response induced by mechanically injuring the leaves and applying caterpillar regurgitant. A specific elicitor in the regurgitant of the caterpillar enhances the amount of several systemically released volatiles. Thus, the systemic release of volatile compounds by herbivore-damaged cotton plants appears to be regulated by at least two different mechanisms.     

Use of synthetic pheromone traps to time control of the lucerne leafroller,Merophyas divulsana

Catches of maleMerophyas divulsana (Walker) (Lepidoptera: Tortricidae) in pheromone traps showed seven peaks per year in lucerne (Medicage sativa L.) between September and April at approximately five week intervals. The trap catches can be used to predict the occurrence of specific stages of the life cycle and periods of damage. By using trap catches to time both harvesting and the application of insecticide, damage to a lucerne crop was reduced. Harvesting was considered to be the more acceptable control strategy.     

The plastic reproductive allocation of the cruciferous perennialRorippa indica in response to different degrees of feeding damage

The degree of feeding damage in the wild to the cruciferous perennial Rorippa indica (L.) Hieron ranged from 0% (not damaged) to 100% (heavily damaged). However, “not damaged” and “heavily damaged” individuals did not differ in the relative suitability of their intrinsic traits for P. rapae, which caused the heaviest damage on the plant. Therefore, the different degrees of feeding damage may be due to variability in the extrinsic traits of the plant, that is, it may be determined by the habitat conditions where individual plants exist. Furthermore, R. indica allocated more resource to seed production at the expense of the roots when it was experimentally subjected to heavy leaf damage. The result suggested that R. indica individuals may escape, by means of seed dispersal and seed dormancy, from unfavorable habitats where they are heavily damaged by herbivores.     

Influence of feeding interval on reproduction and longevity ofPodisus sagitta (Het.: Pentatomidae)

The effect of various feeding intervals on reproduction and longevity of the predatory bugPodisus sagitta (Fabricius) (Heteroptera: Pentatomidae) was studied in the laboratory. Isolated pairs of adult bugs were given moisture in excess and were fed 1 seventh-instar larva of the greater wax moth,Galleria mellonella (L.), with a mean weight of 90 mg every 1, 3, 7, 14 and 21 days. Reproduction ofP. sagitta reflected well the feeding intervals. Females fed at increasing time intervals reduced reproductive outputs by decreasing oviposition frequency and size of egg batches. Predators fed every 21 days produced a mean of only 1.0 egg per day in comparison with 9.9 eggs per day for females fed daily. Longevity of females fed daily was 110.7 days; females fed less frequently tended to live longer, with a maximum mean longevity of 217.5 days for females fed every 14 days. No cannibalism among adults was observed, but females were occasionally seen to feed on their own eggs. Availability of moisture was found to be essential for the predators to survive during periods of low food supplies. These findings are discussed in relation to the predator's adaptation strategies in conditions of prey scarcity.      

Effect of needle damage on the release rate of Masson pine (<Emphasis Type="Italic">Pinus massoniana</Emphasis>) volatiles

The effect of needle damage on the release rate of Masson pine (Pinus massoniana Lamb.) volatiles was examined. Needles were continuously damaged by mechanical damage (MDP) or by feeding of pine caterpillar (Dendrolimus punctatus) larvae (LFP); undamaged pine was used as a control (UDP). Volatiles were collected before damage, and at 16, 24, 40, 48, 64, 72, 88 and 96 h post-damage, and analyzed. The analyses revealed that 19 compounds identified as constitutive volatiles from UDP were terpenes and green leaf odors. The release rate of volatiles from MDP or LFP was higher than that from UDP. At 96 h post-damage, emission from MDP or LFP returned to the same level as that of UDP. Some volatiles, including sabinene, ocimene, limonene-1,2-epoxide, linalool, linalool acetate, germacrene d-4-ol, farnesol, and (E)-4,8-dimethyl-1,3,7-nonatriene were induced by mechanical damage and/or larval attack. Furthermore, the release rate of linalool acetate, farnesol, or (E)-4,8-dimethyl-1,3,7-nonatriene from LFP was higher than that from MDP. Based on an exact estimation of the proportion of damaged pine needles, a significant linear correlation between the release rate of total volatiles identified and the proportion of damaged needles was found in the case of LFP but not MDP.     

Regeneration in fringe mangrove forests damaged by Hurricane Andrew

Mangrove forests along many tropical coastlines are frequently andseverely damaged by hurricanes. The ability of mangrove forests to regeneratefollowing hurricanes has been noted, but changes that occur in vegetationfollowing disturbance by hurricane winds and storm tides have not been studied.We measured changes in plant community structure and environmental variables intwo fringe mangrove forests in south Florida, USA that experienced high windvelocities and storm tides associated with Hurricane Andrew (August1992). Loss of the forest canopy stimulated regeneration via seedlinggrowth and recruitment, as well as resprouting of some trees that survived thehurricane. Initial regeneration differed among species in both forests:Rhizophora mangle L. regenerated primarily via growth ofseedlings present at the time of the hurricane (i.e., release of advancerecruits), but many trees of Avicennia germinans(L.) Stearn and Laguncularia racemosa Gaertn.f.resprouted profusely from dormant epicormic buds. In one forest, which wasformerly dominated by Laguncularia, high densities ofRhizophora seedlings survived the hurricane and grew toform dense stands of saplings and small trees ofRhizophora. In the other forest, there were lowerdensitiesof surviving Rhizophora seedlings (possibly due tohigher storm tide), and extensive bare areas that were colonized byAvicennia, Laguncularia, andherbaceous species. This forest, predominantly Rhizophoraat the time of the hurricane, now contains stands of saplings and small treesofall three species, interspersed with patches dominated by herbaceous plants.These findings indicate that moderately damaged fringe forests may regenerateprimarily via release of Rhizophora advance recruits,leading to single-species stands. In severely damaged forests, seedlingrecruitment may be more important and lead to mixed-species stands.Regeneration of mangrove forests following hurricanes can involve differentpathways produced by complex interactions between resprouting capability,seedling survival, post-hurricane seedling recruitment, and colonizationby herbaceous vegetation. These differences in relative importance ofregeneration pathways, which may result in post-hurricane forestsdifferent from their pre-hurricane structure, suggest that models forregeneration of mangrove forests will be more complex than directregeneration models proposed for other tropical forests whereregeneration after hurricanes is dominated by resprouting.     

The role of the plant in attracting parasitoids: response to progressive mechanical wounding

Based on the model system of Brussels sprouts [Brassica oleracea var. gemmifera (Brassicaceae)], the herbivore cabbage white caterpillar, Pieris brassicae (L.) (Lepidoptera: Pieridae), and the parasitoid wasp, Cotesia glomerata (L.) (Hymenoptera: Braconidae), the influence of plant damage type, and damage duration were assessed on plant volatile emission and subsequent recruitment of natural antagonists of the herbivore. Plants were damaged by three methods for a period of either 3 or 8 h: herbivore damage (HD), progressive mechanical damage, and final mechanical damage inflicted in a single event. Wind‐tunnel bioassays evaluated whether the mode of damage affected female parasitoid oriented flight. After both periods of damage, all treatments were highly significantly preferred by naïve C. glomerata to undamaged control plants. After 3 h, herbivore‐damaged plants were significantly preferred to plants with final damage (FD). Most remarkably, following 8‐h damage, the parasitoid preferred both herbivore‐damaged and progressively damaged plants to plants with FD and did not significantly discriminate between herbivore and progressively damaged plants, thus indicating a similarity in plant response to herbivore and progressive mechanical damage. In addition to wind‐tunnel bioassays, emitted plant volatiles were collected and analysed by thermal desorption gas chromatography/mass spectrometry, following 3 and 8 h of damage in order to correlate volatiles released from different damage types with the attraction of the parasitoid. Differences in volatile profiles from all damage types were similar following both 3 and 8 h of damage, with only (Z)‐3‐hexenyl acetate found to be emitted in significantly higher quantities by final mechanical damage compared with HD after 3 h. In conclusion, the plant's response to progressive mechanical damage was more similar to HD than final mechanical damage deployed at a single point in time, irrespective of damage duration, and C. glomerata did not significantly discriminate between progressive damage and HD.     

Atrazine Tolerance of Grass Species with Potential for Use in Vegetated Filters in Australia

The response of introduced (Pennisetum clandestinum Hochst.) and native (Stipa aristiglumis F. Muell., Themeda australis (R. Br.) Stapf, Danthonia spp. (L.) grasses to the herbicide atrazine was studied in plants with the potential for use in vegetated filters (biofilters) designed to reduce chemical loads in agricultural runoff. The response was detected by photosynthetic inhibition using leaf chlorophyll fluorescence. With continuous short-term (14 days) dosing with atrazine in sand culture, P. clandestinum showed the greatest tolerance, regardless of the dose (20–500 μg/L). In a clay vertosol soil in the glasshouse, the four species were tolerant to longer-term (84 days) application of three successive doses of simulated run-on, each dose containing 100 μg/L atrazine, a concentration which is comparable to the highest reported in runoff from agricultural land in Australia. Even with a subsequent single atrazine dose at ∼ ∼5000 μg/L, established plants of the four species showed signs of quick recovery (7–21 days) to normal photosynthetic activity. In a field experiment with simulated run-on, applied to P. clandestinum pasture in sandy loam soil, repeated doses at concentrations up to 1000 μg/L gave no significant response; only a subsequent single dose of 5000 μg/L had significant effects, from which plants soon recovered. Although damage from atrazine can be demonstrated with continuous dosing in non-adsorbing media, in soil culture the tolerance of the four selected species to repeat doses of atrazine shows they may be used confidently for biofiltering purposes. P. clandestinum was especially tolerant.     

Volatiles released from bean plants in response to agromyzid flies

Liriomyza sativae Blanchard and Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) are two invasive flies in China that have caused economical damage on vegetables and ornamental plants. In this article, we report the profiles of emitted volatiles from healthy, mechanically damaged, and leafminer-damaged bean, Phaseolus vulgaris L., plants. Among 25 emitted volatiles identified, (E)-2-hexen-1-al, (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), (Z)-3-hexenyl acetate, (Z)-3-hexen-1-ol, (syn)- and (anti)-2-methylpropanal oxime, (syn)-2-methylbutanal oxime, linalool, and (E,E)-α-farnesene were consistently released from damaged bean plants. Combined amounts of these nine compounds made up more than 70% of the total volatiles emitted from each treatment. No qualitative differences in volatile emission were found between bean plants damaged by the two fly species; however, amounts of several major compounds induced by L. huidobrensis damage were significantly higher than those from plants damaged by L. sativae. The mechanically damaged plants released a higher proportion of green leaf volatiles than plants in the other treatments, whereas leafminer-damaged plants produced more terpenoids and oximes. Furthermore, the volatile profiles emitted from plants, damaged by adult leafminers, by second instar larvae, and even the plants with empty mines left by leafminer larvae (the pupal stage) were significantly different. The identification of volatile oximes released from damaged plants was confirmed and is discussed in a behavioral and biological control context.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Managing lepidopteran pests in cabbage with herbicide-induced resistance, in combination with a pyrethroid insecticide

S-ethyldipropylthiocarbamate (EPTC) applied as a soil treatment or over-the-top spray on cabbage plants (Brassica oleracea L.) caused the leaves to turn ‘glossy’ for as long as 30 days. EPTC-induced glossy plants were damaged significantly less than untreated plants by diamondback moth,Plutella xylostella (L.), imported cabbage worm,Pieris rapae (L.), and cabbage looper,Trichoplusia ni (Hbn.). Reductions in damage were equivalent to those obtained from treatment with permethrin. When used in combination with permethrin, EPTC provided additive control of damage by these pests. Our calculations show EPTC-induced resistance to be cost-effective. This use of EPTC has several limitations, however. Younger plants (<9 leaves) were killed or injured by the herbicide. The growth of older plants was not affected, but plants did not become glossy for ca. 10 days after they were treated with EPTC. The crop must be protected with insecticides until the plants are mature enough to treat with EPTC, and until treated plants become glossy. In addition, since the glossy trait is only effective against first instar larvae, populations of later instars on glossy plants must be reduced with an application of insecticide. Finally, EPTC formulations are water-soluble and can be washed away from the plants by heavy rains and irrigation, which may make this use of EPTC impractical in some situations. Where its use is practical, and the indicated precautions are taken, EPTC-induced resistance could reduce dependence on chemical insecticides and reduce selection for insecticide resistance in diamondback moth.     

Short feeding period of carrot psyllid (Trioza apicalis) females at early growth stages of carrot reduces yield and causes leaf discolouration

Overwintered adult carrot psyllids [Trioza apicalis Förster (Homoptera: Psylloidea: Triozidae)] damage carrot [(Daucus carota ssp. sativum L.) (Apiaceae)] seedlings by phloem feeding on the leaves. The aim of this study was to investigate the carrot root and shoot growth in relation to carrot psyllid density during early growth stages. One, two, or three carrot psyllids were allowed to feed on carrot seedlings for 3 days. Leaf damage was measured at the 8‐leaf stage, and root, leaf fresh weight, and number of true leaves were measured at harvest. Both the age of the carrot seedling at infestation and the psyllid density had a significant effect on leaf damage at the 8‐leaf stage: seedlings damaged at the cotyledon stage exhibited more leaf damage than seedlings damaged at the 1‐leaf stage. A higher psyllid density significantly reduced the carrot root weight at harvest. The significant interaction of psyllid density with seedling age indicates that differently aged carrot seedlings responded differently to feeding: one psyllid feeding for 3 days at the cotyledon stage caused a significant yield loss, whereas three psyllids were needed to cause the same impact at the 1‐leaf stage. Carrot leaf weight at harvest was not reduced by carrot psyllid feeding: leaves recovered from the damage but roots did not. Our results confirm the farmers’ observations that a trap replacement period of 1 week for carrot psyllid monitoring is too long, especially at the cotyledon stage. Severe leaf discolouration on damaged carrots was observed at harvest. The possible reasons for this discolouration, such as toxin excreted in psyllid saliva or plant pathogenic mycoplasma infection, are discussed.     

Identifying bird cherry-oat aphid Rhopalosiphum padi emigrants, alate exules and gynoparae: application of multivariate methods to morphometric and anatomical features

The host microhabitat location behavior of females of the generalist parasitoid Campoletis sonorensis (Cameron) (Hymenoptera: Ichneumonidae) was studied in a wind tunnel. Visual cues associated with the host plant cotton, Gossypium hirsutum L., were important and significantly more parasitoids completed flights to a damaged 4-leaf cotton plant bearing a Heliothis virescens (F.) (Lepidoptera: Noctuidae) larva and frass than to a similarly damaged single leaf with frass and a larva. This difference in completed flights was not due to differences in amounts of volatiles released by the two stimuli. Both naive and experienced parasitoids responded differently to an undamaged cotton leaf, a mechanially damaged leaf, a naturally damaged leaf with the host removed and a naturally damaged leaf with a host larva. Parasitoids completed significantly fewer flights to the undamaged sources of volatiles than to damaged sources of volatiles. Experienced females responded strongly to all types of damage. The number of flights completed by naive females to the three types of damage differed but not significantly and was less than the number completed by experienced females. Components of the preflight experience were varied to determine which factors were responsible for the higher response of experienced females to the host/plant complex. Oviposition was the most important component of this experience. Contact with host frass or plant damage followed by oviposition did not increase the response over that exhibited by females allowed oviposition only. When frass or damaged plant material were contacted without subsequent oviposition, females completed fewer flights than naive females.     

Lytic enzymes induced by Pseudomonas fluorescens and other biocontrol organisms mediate defence against the anthracnose pathogen in mango

Talc-based bioformulations containing cells of Pseudomonas fluorescens, Bacillus subtilis and Saccharomyces cerevisiae were evaluated for their potential to attack the mango (Mangifera indica L.) anthracnose pathogen Colletotrichum gloeosporioides Penz. under endemic conditions. The preharvest aerial spray was given at fortnightly and monthly intervals. The plant growth-promoting rhizobacteria Pseudomonas fluorescens (FP7) amended with chitin sprayed at fortnightly intervals gave the maximum induction of flowering, a yield attribute in the preharvest stage, consequently reduced latent symptoms were recorded at the postharvest stage. An enormous induction of the defence-mediating lytic enzymes chitinase and β-1,3-glucanase was recorded in colorimetric assay and the expression of discrete bands in native PAGE analysis after FP7 + chitin treatment. The enhanced expression of defence-mediating enzymes may collectively contribute to suppress the anthracnose pathogen, leading to improved yield attributes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of growth period,plant age and changes in solution aluminium concentrations on aluminium toxicity in wheat

The effects of growth period (time between transplanting and harvesting), plant age at which aluminium (Al) was added to solution, changes in Al concentration, and solution culture techniques (monitoring and adjusting solution Al concentrations thrice weekly or weekly replacement of the solutions) were investigated using a low ionic strength (2.7×10^–3 M) solution culture technique. The wheat (Triticum aestivum L.) cultivars Waalt (Al-tolerant) and Warigal (Al-sensitive), or the near isogenic lines bred from these cultivars (RR for the Al-tolerant line and SS for the Al-sensitive line) were grown. In all experiments and treatments, Al additions were required to maintain the nominal concentration. The decline in solution Al concentrations was partially attributed to formation of an Al-hydroxy-phosphate precipitate with an Al:P molar ratio of 2.8 to 4.0. Increasing the growth period from 14 to 28 days increased Al sensitivity in Warigal but not in Waalt. When plants were exposed to Al for the same time, increasing the age of the plants that Al was added to solution decreased sensitivity to Al. Differential Al tolerance between the two lines was evident when solutions were monitored thrice weekly or replaced weekly. However, the Al concentration required to reduce relative yield by a given amount when the solutions were replaced weekly was about twice that when the solutions were monitored. With a constant growth period of 28 days, increasing solution Al concentrations for 3 or more days resulted in decreased yields at harvest. The exact effect depended on the cultivar, plant part (tops or roots), when solution Al concentrations were increased and the duration of the increase. For example, increasing Al concentrations from 5 M to 20 M for 10 days reduced yield in the RR line by approximately 50% in the tops and 30% in the roots beyond the effect of 5 M but had no effect in the SS line due to yields already being low at 5 M. Adding 10 M Al to solution for 6 days at the beginning of the experiment reduced yield by 25% in the RR line and 50% in the SS line. In contrast, adding 10 M Al for 6 days in the middle of the growth cycle had no effect on the RR line but reduced yield by approximately 25% in the SS line. These results show that growth period, the age of the plants at which Al is added and the technique used (monitored or weekly replacement) all need to be considered when comparing results from different experiments. These results also show that the Al concentrations in solution need to be regularly monitored in long term experiments.     

伤害和挥发物对棉花花外蜜的诱导效应

植物花外蜜的分泌是一种植物间接防御反应。为了明确植食性昆虫、机械伤和机械伤诱导的挥发性气体在植物花外蜜诱导分泌中的作用,分析了咀嚼式口器昆虫棉铃虫Helicoverpa armigera(Hübner)、刺吸式口器昆虫棉蚜Aphis gossypii Glover取食、剪刀机械伤、剪刀机械伤+棉铃虫反吐物、针刺机械伤以及机械伤诱导挥发物、顺式-茉莉酮对棉花Gossypium hirsutum L.叶片花外蜜分泌量的影响。结果表明,棉铃虫取食、剪刀机械伤、剪刀机械伤+棉铃虫反吐物处理均显著增加了被处理叶片花外蜜的分泌量。棉花花外蜜的诱导效应在处理叶片上表现明显,并且在较幼嫩的第3片真叶上也有系统性增长。顺式-茉莉酮和机械伤挥发物处理1 d对棉花较幼嫩的第4、5片真叶花外蜜有诱导效应。棉花叶片花外蜜的诱导主要与植物组织损伤有关;不同口器类型的昆虫对棉花叶片花外蜜的诱导量不同,咀嚼式口器的棉铃虫对棉花花外蜜的诱导强度显著高于刺吸式口器的棉蚜;顺式-茉莉酮和机械伤诱导的挥发物能作为棉花植株间交流的信息物质诱导棉花幼嫩叶片花外蜜的分泌。