Effect of temperature on the life history of Dysmicoccus neobrevipes (Hemiptera: Pseudoccocidae): An invasive species of gray pineapple mealybug in South China

The gray pineapple mealybug, Dysmicoccus neobrevipes Beardsley, is an invasive pest that during recent years has caused serious damage on Sisal (Agave sisalana Perrine) crops in South China. The biology of D. neobrevipes including its development, survivorship, longevity and reproduction was investigated at six constant temperatures (17, 20, 23, 26, 29 and 32 °C) under laboratory conditions. Results indicated that the developmental periods of D. neobrevipes females (from the first instar nymph to adult) shortened from 55.4 days at 17 °C to 16.9 days at 29 °C, while the males' decreased from 54.0 days at 17 °C to 15.8 days at 32 °C. The highest survivorship of D. neobrevipes from the first instar nymph to adult was recorded at 29 °C; 88.8% for females and 89.2% for males. The average longevity of females was 95.0 days at 17 °C, but decreased to 30.0 days at 26 °C. This was still significantly longer than those of males; 5.6 days at 17 °C and 2.3 days at 32 °C. The average number of nymphs laid per female increased with increasing temperature and reached a maximum of 409.4 nymphs at 23 °C. The intrinsic rates of increase (r_m) of D. neobrevipes at the range of temperatures between 17 and 32 °C were 0.0287, 0.0613, 0.0941, 0.1131, 0.1202 and 0.0485, respectively. The lower temperature thresholds for females and males of D. neobrevipes from the 1st instar nymph to adult estimated using the linear model were 8.7 and 10.3 °C, respectively. The thermal constants for females and males were 370.4 and 312.5DD, respectively. The results indicate that temperature has significant effects on the biology of D. neobrevipes and that the optimum temperature range for its population growth is 23–29 °C.     

Effects of leaf scales of different pineapple cultivars on the epiphytic stage of Fusarium guttiforme

The fungus Fusarium guttiforme (Syn. F. subglutinans f. sp. ananas) is responsible for fusariosis, one of the main phytosanitary threats to pineapple (Ananas comosus var. comosus). A structural study comparing epidermal differences in pineapple cultivars resistant and susceptible to fusariosis was performed, relating properties of the epidermis to known susceptibility to the disease. The basal, non-chlorophylled, portions of mature leaves of pineapple plants were analyzed by light and electron microscopy. All cultivars showed common morpho-anatomic aspects characteristic of Bromeliaceae, such as scutiform scales and unstratified epidermis. However, cultivar Vitoria (resistant) had less scales than cultivars Smooth Cayenne (susceptible, intermediate severity) and Perola (susceptible, with extreme severity of fusariosis symptoms). Inoculation of conidia suspension (10⁵ conidia ml⁻¹) of the fungus F. guttiforme to leaves and harvesting 24 h later yielded numbers of viable colonies related to the density of leaf scales. This suggests that scales can act as havens for fungal conidia and favour the epiphytic stage of the fungus on pineapple plants, and are involved in the interaction of plant and pathogen. A reduction in scale numbers was related to lower infection levels and is relevant to the future breeding programme for development of new pineapple cultivars resistant to fusariosis and their involvement in integrated control strategies.     

Effects of different brassicaceous host plants on the fitness of Pieris brassicae (L.)

Pieris brassicae (L.) is a destructive cosmopolitan pest of cruciferous crops. It is present wherever its host plants occur and it is considered to be one of the most widely distributed of all the Lepidoptera. We investigated the affect of various host plants on the fitness of P. brassicae to survive, develop and reproduce. We quantified development time, survival and mortality on cabbage (Brassica oleracea capitata), cauliflower (Brassica oleracea botrytis), radish (Raphanus sativus), broccoli (Brassica oleracea italica), and mustard (Brassica campestris) under laboratory conditions. The developmental time from eggs to adult eclosion was the shortest (30.3 days) on cabbage and the longest (38.0 days) on radish. However, adult longevity was significantly (P < 0.001) greatest on cabbage compared with the other host plants tested. Similarly, the developmental rate of P. brassicae was found to be faster on cabbage than other cole crops. Moreover, the lowest immature mortality was evident on cabbage and highest on mustard and radish. Differences in reproductive parameters of the P. brassicae among host plants were analyzed using pseudo-values, which were produced by jackknife re-sampling. The data showed that the higher intrinsic rate of natural increase (0.116 females/female/day) was found on cabbage. Cabbage was recognized as the most suitable host for P. brassicae because of shorter developmental period, higher percentage survival, lower doubling time (6.00), and higher number of adult emergence (29.7%).     

Differential response of two pineapple cultivars (Ananas comosus (L.) Merr.) to SAR and ISR inducers against the nematode Rotylenchulus reniformis

We hypothesized that inducing systemic resistances can contribute to the control of the nematode Rotylenchulus reniformis in pineapple. In greenhouse experiments conducted in Martinique, the pineapple cultivars Smooth Cayenne and MD-2 were treated with methyljasmonate (JAME) and salicylic acid (SA), elicitors of induced systemic resistance (ISR) and systemic acquired resistance (SAR). The efficacy of the elicitors was tested by inoculating plantlets grown in individual pots with a monospecific population of R. reniformis reared on Vigna unguiculata. The final nematode populations, 45 days after inoculation on MD-2 treated with JAME were reduced by 67.0% (p = 0.006). Nematode populations on MD-2 plants treated with SA were reduced by 55.8% (p = 0.016). Nematode populations on SC were not reduced by the elicitors. In a second experiment, using split-root systems, JAME was applied to MD-2 plantlets and enzymatic activities involved in plant defense and stress responses were monitored for 14 h after treatment. Additional pots were inoculated with nematodes 24 h after JAME treatment and examined ten days later. Transient stress was observed along with an increase in enzymatic response after inoculation with nematodes. These results showed that the MD-2 was primed through an ISR by JAME. The question now arises whether ISR can be specifically induced only in certain pineapple cultivars. Results are discussed from the perspective of introducing new strategies to manage pineapple nematodes.     

Effect of different host plants on the fitness of diamond-back moth, Plutella xylostella (Lepidoptera: Plutellidae)

The diamond-back moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae) is a destructive cosmopolitan pest of cruciferous crops. The pest is present wherever its host plants exist and is considered to be one of the most widely distributed of all the Lepidoptera. We investigated the effect of various host plants on the fitness of P. xylostella and tested the hypothesis by studying development time, growth, fecundity and survival on cabbage (Brassica oleracea capitata), cauliflower (Brassica oleracea botrytis), radish (Raphanus sativus), turnip (Brassica rapa), mustard (Brassica compestris) and canola (Brassica napus var. canola). The developmental time from eggs to adult eclosion was the shortest (10 days) on canola and the longest (13 days) on turnip. Fecundity was greatest on canola (350) followed by cauliflower (268 eggs) by females eclosed from the pupae reared on canola and cauliflower, respectively, while the minimum numbers of eggs (184) were observed on cabbage. The number of eggs hatched was the highest (80%) when larvae fed on cauliflower. Survival to the adult stage was the highest (94%) on mustard followed by cauliflower and lowest (64%) on turnip. The net replacement rate was lowest for populations reared on cabbage (32.3), which was also reflected by the lowest intrinsic rate of population increase (0.20). The correlation between the intrinsic rate of population increase (r_m) and the mean relative growth rate was significant (t = 20.02 d.f. = 4, P < 0.05). Canola and mustard proved to be the most suitable hosts for P. xylostella because of shorter developmental period, higher percentage of survival and higher number of eggs. The data point to the role of host plants in increasing local P. xylostella populations.     

Influence of plant leaf surface on the development,reproduction and life table parameters of the predacious mite, Agistemus exsertus Gonzalez (Acari: Stigmaeidae)

The influence of leaf surfaces of different host plants on the biology and life table parameters of the predacious mite, Agistemus exsertus Gonzalez was studied in the laboratory. A. exsertus successfully developed and reproduced on all tested plant leaves. Smooth, glabrous pear leaves accelerated the development of A. exsertus and showed the shortest mean generation time. Slightly rough, slightly hairy leaves of mulberry and acalypha were the most suitable surface for oviposition of the predator. These leaves exhibited the highest fecundity and net reproductive rate. On the other hand, leaves of rough, pubescent apple and scabrous, bristly lantana were the least suitable surface for oviposition of A. exsertus. They showed the lowest fecundity and net reproductive rate. Acalypha leaves exhibited the highest intrinsic rate of increase for the predator, whereas lantana leaves showed the lowest value. This difference in the predator response to leaf surfaces of host plants should be considered to enhance the role of the predator in biological control programs.     

Differential reproductive maturity between geographically separated populations of Homalodisca vitripennis (Germar) in California

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar), is native to the southeastern United States and northeastern Mexico. It was detected in southern California in the late 1980s and in the San Joaquin Valley in 1999, where it transmits the bacterium Xylella fastidiosa to grapevines and other crops. The reproductive success of hybrid and pure line H. vitripennis from two geographically separated populations in California (Riverside (RIV) and Bakersfield (BAK)) was evaluated under identical conditions. The RIV and BAK populations had different preoviposition periods that persisted through the second generation of each lineage. From adult molt, the preoviposition period in both female generations was significantly shorter for RIV (F₀ = 28.2 days and F₁ = 62.3 days) than BAK females (F₀ = 46.1 days and F₁ = 170.4 days). After a 21-day mating period, F₀ and F₁ females deposited on average 391 (range, 21–967) and 196 (range, 0–755) eggs, respectively, without significant differences in fecundity among the F₀ and F₁ mating pair treatments. Egg accumulation rates among F₁ treatments showed that females in the RIV groups rapidly deposited their eggs within the first 120 days after adult molt while BAK females maintained a steady accumulation rate during their life. The performance of both hybrid lines was intermediate between the pure lineages. The F₀ mating pairs: ♀RIV × ♂RIV, ♀RIV × ♂BAK, ♀BAK × ♂RIV, and ♀BAK × ♂BAK produced on average 185, 94, 79, and 0 viable eggs, respectively, which suggested a delayed sexual maturity of BAK males and females. The proportion of viable eggs deposited decreased gradually, which suggests that females completely exhausted sperm reserves. From a management perspective, delayed reproductive maturity and polyandry are weak links in H. vitripennis’ biology that may be exploited through mating disruption or insect sterilization strategies to reduce population growth and augment pressure by natural enemies.     

Insecticide-induced enhancement of flight capacity of the brown planthopper Nilaparvata lugens Stål (Hemiptera: Delphacidae)

The brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a long-distance migratory insect pest in temperate eastern Asia and a typical recurrent pest induced by pesticides. We investigated the effect of sublethal concentrations of insecticides on the flight capacity on this species. An automated flight-mill system was used to assess the flight capacity of adults reared on untreated and insecticide-treated plants. In most instances, the flight duration of adult females exposed to high concentrations of imidacloprid, triazophos or deltamethrin was significantly greater than that of untreated controls. Compared to the controls, the flight duration of females increased by 140% (from 103 to 245.9 min), 119% (from 103 to 226 min) and 78% (from 103 to 183.3 min) with 10 ppm imidacloprid, 40 ppm triazophos and 3 ppm deltamethrin, respectively, yet no significant difference in the flight duration of males was found between the insecticide treatments and the controls. The high concentrations of the three insecticides significantly enhanced the flight speed and the flight distance of both males and females, with the exception of the flight speed of adult males treated with deltamethrin. For example, the flight speed of adult females and males treated with 10 ppm imidacloprid, 40 ppm triazophos and 6 ppm deltamethrin increased by 75% (from 0.39 to 0.68 km/h), 154% (from 0.39 to 0.98 km/h) and 124% (from 0.39 to 0.87 km/h) for females and by 141% (from 0.32 to 0.77 km/h), 73% (from 0.32 to 0.55 km/h) and 48% (from 0.32 to 0.47 km/h) for males, respectively, compared to the controls. In addition, the percentages of individuals treated with imidacloprid and triazophos flying for over 60 min doubled compared to the control. These findings are relevant for understanding the migration and outbreak patterns of N. lugens.     

Population density and life-history parameters of the psyllid Bactericera nigricornis (Forster) on four commercial cultivars of potato

The psyllid Bactericera nigricornis (Forster) (Hemiptera: Triozidae) is one of the most important pests of potato, Solanum tuberosum L., in the Ardabil region, Iran. The use of host plant resistance is an essential component of the integrated management of B. nigricornis. In this study, we investigated the population density of B. nigricornis on four commercial cultivars of potato under field conditions and its life-history parameters under laboratory conditions. In field experiments, the lowest and highest densities of B. nigricornis were observed on cvs. Agria and Marfona, respectively. Population densities did not differ significantly between cvs. Kaiserkrone and Satina. In experiments on life-history parameters, the longest and shortest developmental times of nymphs were observed on cv. Agria (22.3 days) and cv. Marfona (18.2 days). The developmental time of nymphs on Kaiserkrone did not differ significantly from that on Satina. The lowest number of eggs laid per female (47.2) and the lowest survival rate (50%) were observed on Agria. The survival rate on Agria did not differ significantly from that on Kaiserkrone and Satina. The intrinsic rate of natural increase (r_m) and population growth rate (λ) were lowest on Agria and highest on Marfona. The generation time on Agria and Kaiserkrone was significantly longer than on Satina and Marfona. The doubling time (DT) was longest on Agria (15.9 days) and shortest on Marfona (11.8 days). Amongst the cultivars investigated, host plant resistance acted by decreasing the numbers of eggs laid per female, increasing the development time and reducing the survival rate of B. nigricornis, so decreasing population growth. Of the cultivars tested, Agria is the most resistant host and has potential for use in the integrated management of B. nigricornis on potato.     

The effects of nitrogen rate and the ratio of NO3:NH4 on Bemisia tabaci populations in hydroponic tomato crops

Nitrogen fertilization is one of the factors that influences Bemisia tabaci (Gennadius) population density. The aim of this study was to determine the effects of three N application rates (75, 205 and 335 mg/l) and three ratios of NO₃⁻:NH₄⁺ ions (92:8, 75:25 and 55:45) in standard nutrient solution (205 mg/l N) on the population density of B. tabaci. The experiments were conducted on spring-summer hydroponic crops of tomato. The effect of plant stratum on the whitefly population was also determined. The aggregation of B. tabaci adults as well as their oviposition rate was higher at 205 and 335 mg/l N than on plants grown at 75 mg/l N. By the end of the experiment (60 d after infestation), the number of nymphs on plants at 205 mg/l N was higher than on plants at 75 mg/l N. The number of pupae was lowest on plants supplied with 75 mg/l N. An increase in NH₄⁺ percentage in standard nutrient solution (from 25% to 45% of the total N) reduced adult population density and oviposition rate. The density of nymphs and pupae, at 60 d after infestation, was lower on the tomato plants grown at 75:25 and 55:45 NO₃⁻:NH₄⁺ ratios compared to the 92:8 ratio. The 75:25 and 55:45 NO₃⁻:NH₄⁺ ratios resulted in a higher incidence of blossom-end rot of tomato fruit, with a lower incidence of disorder at 75:25 than at the 55:45 ratio. Plant stratum influenced adult whitefly distribution in two years of the study. Middle stratum leaves were more attractive to adults in both years. The results demonstrate the effects of N fertilization (N rate and the ratio of NO₃⁻:NH₄⁺) and plant stratum on B. tabaci population density.     

Volatile organic compounds as a diagnostic marker of late blight infected potato plants: A pilot study

Volatiles from potato plants infected with Phytophthora infestans (Mont.) de Bary were monitored by in situ headspace sampling. The sampling was done in four periods i.e. 28–42, 52–66, 76–90, and 100–114 h after inoculation (HAI). The headspace samples were analyzed by a gas chromatography–flame ionization detector (GC–FID) to assess the differences in volatile fingerprints between the infected-plant group and control groups, i.e. non-inoculated-plant and empty-vessel groups. The samples were subsequently analyzed by gas chromatography–mass spectrometry to identify specific peaks observed by GC–FID. Spore germination, infection, symptom development and sporulation were also monitored to ascertain the disease developmental stage when marker volatiles were first generated. The first symptoms of infection were visible after two days. Three marker volatiles i.e. (E)-2-hexenal, 5-ethyl-2(5H)-furanone and benzene-ethanol were found in the third and fourth trapping periods (3–4 days after inoculation) when sporangiophores were already formed. The volatile metabolites from blighted plants could be applied for sensor development to detect the occurrence of the disease in the field as well as for investigation of volatile production in relation to plant responses to infection.     

Population dynamics of Xanthomonas campestris pv. vitians on different plant species and management of bacterial leaf spot of lettuce under greenhouse conditions

The population dynamics of Xanthomonas campestris pv. vitians (Xcv) was studied both externally and internally in lettuce, tomato and pepper plants. In addition, the application of bactericides during transplant production period was carried out for the management of bacterial leaf spot of lettuce under greenhouse conditions. Epiphytic populations of Xcv were recovered on leaves of lettuce plants (10⁵ CFU/g) 5 weeks after sprayed than the other plant species when inoculated with 10⁸ CFU/ml of Xcv. When plants of each crop species infiltrated with the bacterium at 10⁵ CFU/ml, the highest populations were developed in lettuce (10⁸ CFU/cm²) followed by pepper with 10⁶ CFU/cm² and tomato with 10⁵ CFU/cm² 10-days after infiltration. Application of a mixture of Maneb and Kocide or Kocide alone as a foliar spray on lettuce significantly reduced the incidence and disease severity of bacterial leaf spot by 29 and 27% respectively. Spread of the bacterium and development of the disease may partly be managed by avoiding intercropping of these plants commonly grown in close proximity to lettuce. For the management of leaf-associated populations of Xcv in lettuce, use of a mixture of Maneb and Kocide is advocated to minimize the effect of attacks.     

Insecticide-induced increase in the protein content of male accessory glands and its effect on the fecundity of females in the brown planthopper Nilaparvata lugens Stål (Hemiptera: Delphacidae)

The brown planthopper Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) is a classical resurgent rice pest induced by insecticides. The past focus on resurgence mechanisms has been on the stimulation of the reproduction of adult females induced by insecticides. To date, the role that males play as a resurgence of N. lugens has not been investigated. The present study examined changes in protein levels in both male accessory glands and female ovaries induced by the insecticides triazophos and deltamethrin as well as the stimulating effect of treated males on the fecundity of adult females via mating following foliar sprays of the insecticides. For adults that had been exposed as nymphs to treated rice plants, the protein content in both the male accessory glands and in the female ovaries of N. lugens were significantly affected by male mating status, insecticide and insecticide concentration. There was a higher protein content in male accessory glands when males were exposed to triazophos as third instars compared to fifth instars, and there was a higher protein content before mating compared to after mating. In addition, the protein levels in male accessory glands after mating for individuals exposed to high doses of the two insecticides as 3rd and 5th instars were significantly lower than untreated control except for exposed to triazophos as 3rd instar, indicating that treated males transferred more male accessory gland protein to adult females via mating. The protein content was also affected by different combinations of treated mating pairs. Adult males (♂_t) developed from third instar nymphs treated with triazophos stimulated the fecundity of the female significantly via mating (♂_t × ♀_ck) with untreated females (♀_ck) (control females), increasing the reproductive rate by 43.5% as compared to the mating (♂_ck × ♀_ck) of untreated males and females. Also, the fecundity of the females after the mating (♂_t × ♀_t) of treated males and females was significantly higher than that after the mating (♂_ck × ♀_t) of untreated males with treated females. These findings indicated that the reproductive effects of insecticide on males can be transferred to females via mating. The present findings provide valuable information for understanding the potential role that males play in the pesticide-induced resurgence of N. lugens.     

Host selection behavior of Bagrada hilaris (Hemiptera: Pentatomidae) on commercial cruciferous host plants

A series of host-choice tests were conducted under greenhouse conditions to evaluate the host selection behavior of the Bagrada bug, Bagrada hilaris on commercial cruciferous seedlings. In addition, a separate choice test was conducted to investigate the selection behavior of B. hilaris adults for broccoli plants of various growth stages: cotyledon, 1-leaf, 2-leaf, and 4-leaf plant stages. In comparing host selection among the commercial seedlings, observations on host attractiveness, host acceptance and host susceptibility of the cruciferous cultivars to B. hilaris adults were measured by recording numbers of adults per plant, the time at which feeding damage was first observed, and the time plant mortality occurred for each cultivar, respectively. Results showed that significantly more adult B. hilaris were attracted to a commercial radish cultivar than all other hosts, followed by red and green cabbage. Measurements of host acceptance varied among the cruciferous cultivars, however in terms of feeding damage, alyssum, arugula and broccoli appeared to be relatively less acceptable hosts for B. hilaris. Similarly, all host plants were susceptible to B. hilaris feeding damage and plant mortality varied among cultivars. In the broccoli growth-stage trials, experiments were designed in a similar fashion except that the experiment was conducted in plastic cages. A greater number of B. hilaris adults were attracted to 4-leaf-stage broccoli than other growth stages, but feeding damage was observed more quickly on cotyledon-stage plants. The implications of these findings for developing alternative pest management approaches for B. hilaris in commercial cruciferous crops are discussed.     

Lethal and sublethal effects of buprofezin and imidacloprid on Bemisia tabaci (Hemiptera: Aleyrodidae)

The sweetpotato whitefly, Bemisia tabaci (Gennadius), has become a major threat to agriculture worldwide. The development of insecticide resistance in B. tabaci has necessitated the exploration of new management tactics. The toxicity of imidacloprid and buprofezin to various life stages of B. tabaci was determined in the laboratory. Also, the sublethal effects of both insecticides were studied on demographic and biological parameters of B. tabaci. Both insecticides were very toxic against first stage larvae of the pest with LC₅₀ values of 1.0 and 19.3 ppm for buprofezin and imidacloprid, respectively. Toxicities decreased between successive stages (LC₅₀ values ranging from 1.0 to 2854.0 ppm). The LC₅₀ values of imidacloprid for adult males, females and eggs were 11.8, 71.6 and 151.0 ppm, respectively. Buprofezin had no significant effect on adults and eggs. The sublethal concentration of imidacloprid had no significant effect on demographic and biological parameters of B. tabaci but the maximal value for the mean generation time (T) (18.8 day) was observed in imidacloprid treatment. Buprofezin significantly decreased stable population and biological parameters of B. tabaci except it did not decrease the rate of population increase or the sex ratio of offspring.     

Management of the root-knot nematode Meloidogyne incognita on tomato with combinations of different biocontrol organisms

The nematicidal effect of Pseudomonas fluorescens, Paecilomyces lilacinus, Pichia guilliermondii and Calothrix parietina singly or in combination was tested against root-knot nematode, Meloidogyne incognita. Treatments with P. fluorescens and P. lilacinus caused mortality of M. incognita as 45% and 30% of juveniles after 48 h of exposures, respectively compared to water control in vitro. Under greenhouse conditions, all treatments reduced the disease severity and enhanced plant growth compared to untreated control. Application of P. fluorescens, P. lilacinus and P. guilliermondii Moh 10 was more effective compared to C. parietina. There was a negative interaction between C. parietina and either P. lilacinus or P. guilliermondii. Fresh and dry weight of shoots and roots of plants were significantly reduced as a result of infection with M. incognita, however application of biocontrol agents singly or in mix recovered this reduction. Moreover, they enhanced the growth parameters compared with the control. Our results proved that application of different biocontrol agents (P. fluorescens, P. lilacinus and P. guilliermondii) not only has a lethal effect on nematode, but also enhances the plant growth, supplying many nutritional elements and induction the systemic resistance in plants. Presence of C. parietina as a soil inhabitant cyanobacterium could antagonize biocontrol agents leading to the reduction of their practical efficiency in soil.     

Effect of Trichoderma asperellum and arbuscular mycorrhizal fungi on cacao growth and resistance against black pod disease

Arbuscular mycorrhizal fungi (AMF) and members of the genus Trichoderma have emerged as promising groups of microbial inoculants that can induce plant growth and resistance to disease. This study aimed at investigating the potential of AMF and a strain (PR11) of Trichoderma asperellum to promote cacao growth and induce resistance against Phytophthora megakarya. Cacao seedlings were either non-inoculated, or inoculated with the saprophytic fungus T. asperellum and/or a mixture of two different mycorrhizal fungi, Gigaspora margarita and Acaulospora tuberculata. Eighteen weeks after planting, a series of morphological as well as biochemical changes, which are considered to be part of the plant defense response, were measured after a challenge inoculation of the leaves with zoospores of P. megakarya. Inoculation with AMF and T. asperellum alone was essential for the promotion of plant growth. Significant increase in plant height, root and shoot fresh weights, as well as phosphorous uptake was recorded in comparison to non-inoculated control plants. However, dual inoculation of cacao seedlings with T. asperellum and AMF did not always positively benefit the plants. Leaf inoculation showed variation among the treatments, with the lowest disease index (highest level of resistance) recorded in plants inoculated with either AMF or T. asperellum only. This came along with a high synthesis of amino acids and phenolic compounds in both healthy and infected leaves, suggesting that these metabolites are implicated in disease resistance.     

Insecticidal activities of crude extracts and phospholipids from Chenopodium ficifolium against melon and cotton aphid, Aphis gossypii

Several organic solvent extracts of Chenopodium ficifolium were tested for their insecticidal activity against melon and cotton aphid, Aphis gossypii, on cucumber plants. Both methanol and ethanol extracts, at 5000 μg ml⁻¹, were highly active giving over 80% control. The other crude extracts displayed moderate or weak insecticidal activity giving control in the range of 16–69%. Two phospholipids were isolated as insecticidal active substances from C. ficifolium. Their chemical structures were identified as 1-palmitoyl-2-(3-trans)-hexadecenoyl-sn-glycero-3-phosphoglycerol and 1-palmitoyl-2-linoleoyl-3-glycerophosphocholine by GC–MS, EDS, mass and NMR spectral analyses. Both compounds displayed a dose-dependent mortality of A. gossypii. Furthermore, the liquid formulation that was obtained by partitioning with n-hexane from the methanol extract of C. ficifolium controlled melon and cotton aphid on cucumber plants effectively. These results indicate that extracts of C. ficifolium have potential for development as botanical insecticides for controlling A. gossypii infesting cucumber plants.     

Biological control of Macrophomina phaseolina by chemotactic fluorescent Pseudomonas aeruginosa PN1 and its plant growth promotory activity in chir-pine

Ten strains of Pseudomonas aeruginosa (PN1 ˜ PN10) isolated from rhizosphere of chir-pine were tested for their plant growth promontory properties and antagonistic activities against Macrophomina phaseolina in vitro and in vivo. P. aeruginosa PN1 produced siderophore, IAA, cyanogen and solubilized phosphorus, besides producing chitinase and β-1,3-glucanase. In dual culture, P. aeruginosa PN1 caused 69% colony growth inhibition. However, cell free culture filtrate also posed inhibitory effect but to a lesser extent. After 90 days, P. aeruginosa PN1 increased plant growth and biomass in pots trial containing M. phaseolina-infested soil. PN1 showed the strong chemotaxis toward root exudates resulting in effective root colonization. Moreover, increased population in rhizosphere of these bacteria was also recorded after 90 days of treatment. Thus, chemotactic fluorescent P. aeruginosa PN1 exhibited strong antagonistic property against M. phaseolina, suppressed the disease and improved plant growth of the seedlings of chir-pine proving potential biocontrol agent.     

Efficacy of plant extracts and biocontrol agents against Pythium aphanidermatum inciting chilli damping-off

The fungitoxic effects of 66 medicinal plants belonging to different families were evaluated in vitro on Pythium aphanidermatum, the causal agent of chilli damping-off. Of these, Zimmu leaf extract (Allium sativum L. × Allium cepa L.) showed the highest inhibition of mycelial growth of P. aphanidermatum (13.7 mm). The antimicrobial compounds were isolated from Zimmu leaf extract and 22 compounds were identified through gas chromatography mass spectroscopy (GC–MS). Biocontrol agents Trichoderma viride and Pseudomonas fluorescens and Zimmu extract were also tested alone and together in vitro and in vivo experiments for control of P. aphanidermatum. The in vitro studies revealed that combination of T. viride + P. fluorescens + Zimmu leaf extract showed the highest mycelial growth inhibition over the control. Both antagonists were compatible with each other and with Zimmu leaf extract. The pot culture studies revealed that seed treatment with combined application of T. viride + P. fluorescens + Zimmu leaf extract was superior in reducing the pre and post-emergence damping-off incidence (8.3 and 17.0%, respectively), and increased the plant growth and yield (shoot length and root length of 13.7 and 6.3 cm, 146 g/plant, respectively) of chilli when compared to control.