Integrating cultural control methods for tomato late blight (Phytophthora infestans) in Uganda

Cultural control measures against tomato late blight (Phytophthora infestans) were evaluated in six field experiments over 3 years in Uganda. Each experiment included sanitation (removal of diseased plant tissues), fungicide (mancozeb) application, and an untreated control, as standard treatments. Late blight incidence and severity were greatly reduced by sanitation, without reducing the number of healthy leaves; however, tomato growth and production were adversely affected. Fungicide treated plants retained the highest numbers of flowers and attached fruits and gave the highest yields. Three cultural practices were evaluated in repeated experiments for their effectiveness in alleviating the adverse effects of sanitation. Tomatoes grown within plastic shelters early in the production cycle were taller, and had more healthy leaves than those grown late. The numbers of diseased leaves and disease severity were equally low in sanitation alone and plastic shelter/with sanitation treatments. Flower and fruit production were significantly higher when tomatoes were grown under early shelters with sanitation than with sanitation alone. Planting density was increased without significant effects on late blight and tomato growth and production. Intercropping tomato with soybean (Glycine max) or sesame (Sesamum indicum), with sanitation, limited late blight development, but taller intercrops suppressed tomato growth and production. Integrated treatments (combining plastic shelters, a sesame intercrop and high tomato planting density) were evaluated, with and without sanitation, against the fungicide mancozeb. The mean numbers of healthy leaves in the integrated treatments were not significantly less than with fungicide treatment. Late blight incidence and severity were higher in the integrated plots without than with sanitation. The numbers of flowers and attached fruits were not significantly less in integrated treatments than in fungicide treated plots, but tomato yield was highest with fungicide treatment.     

Rhizobacterial induction of systemic resistance in tomato plants: non-specific protection and increase in enzyme activities

Rhizobacteria B101R, B212R, and A068R, selected as inducers of systemic resistance against Pseudomonas syringae pv. tomato, were tested individually for biological control of multiple pathogens causing foliar diseases in tomato plants. Greenhouse bioassays were carried with five pathogens—Alternaria solani (early blight), Corynespora cassiicola (foliar blight), Oidium lycopersici (powdery mildew), Stemphilium solani (leaf spot), and Xanthomonas campestris pv. vesicatoria (bacterial spot). The level of control achieved by each rhizobacterium varied with the pathosystem studied. Isolate B101R afforded reduced disease intensity in terms of average number of leaf lesions as compared to the treatment control, protection against A. solani, S. solani, and O. lycopersici. Lipoxygenase, phenylalanine amonia-lyase, and peroxidase activities were estimated spectrophotometrically in extracts of plants grown from seeds that were microbiolized with rhizobacterium B101R, and inoculated with P. syringae pv. tomato. Increases in peroxidase and lipoxygenase activities were detected in foliar extracts from plants whose seeds had been microbiolized, while no increase in phenylalanine amonia-lyase activity was observed.     

Mesh crop covers improve potato yield and inhibit tomato potato psyllid and blight: The roles of mesh pore size and ultraviolet radiation

Crop losses caused by the tomato potato psyllid (TPP; Bactericera cockerelli) and blight (Alternaria solani; Phytophthora infestans) continue to be major concerns for potato (Solanum tuberosum) growers worldwide, and commercial crops often require frequent use of agrichemicals to maintain tuber yield and quality. Nevertheless, a paradigm shift is unfolding in crop protection where new tools, such as physical barriers and light‐modifying filters, are being used to develop chemical‐free approaches for pest and disease control. In this study, we examined the use of crop covers as a non‐chemical method for controlling TPP and reducing blight in field potatoes. Our study demonstrated that those plants grown under mesh covers exhibited reduced levels of blight, TPP and associated psyllid yellows. Additionally, potatoes grown under mesh covers exhibited increased yield (91.4 ± 6.9 SD t/ha) compared with both uncovered control plants (75.0 ± 11.8 t/ha) and plants grown using agrichemical pest control (84.5 ± 10.8 t/ha). The plants grown under mesh produced fewer smaller tubers, with increased average and maximum tuber size, so that marketable yield (tubers ≥60 g) was also increased (83.5 ± 7.5 t/ha), compared with that achieved for uncovered control plants (60.0 ± 8.3 t/ha) and plants grown using agrichemicals (69.6 ± 9.2 t/ha). A second field experiment suggested that the incidence of TPP foliage damage and the development of blight were lowest when the passage of ambient ultraviolet (UV) radiation through the crop cover was reduced. This hypothesis was supported by a third trial where potatoes grown outdoors in pots exhibited reduced TPP foliage damage and fewer resident TPP when grown under UV‐blocking plastic screens. The results of these experiments suggest that the use of mesh covers offers new opportunities to sustainably protect potato crops both by acting as a physical barrier and by modifying the wavelength of light incident on the crop.     

The prevention of seed-borne diseases of flax by seed disinfection II. Comparison of the dusting, short wet and fixation methods of treatment

Suitable organo-mercury preparations applied by the short wet method of seed treatment and organo-mercury powders, of the type used for treating cereal seeds, fixed to the seed with water by the fixation method of treatment, gave as satisfactory control of seedling blight and better control of stem break and browning than a proprietary dry fungicide containing tetra-methyl thiuram disulphide (Nomersan) applied at the rate of 12 oz./cwt. of seed.
Treatment of seed heavily infected with Polyspora Lint using an efficient fungicide resulted in highly significant increases in crop and fibre yields, while in the case of seed heavily infected with Colletotrichum Lini similar treatments significantly increased the yield of fibre but not the crop yield. Some treatments significantly increased the crop and fibre yields even when the seed used was only slightly contaminated with P. Lini and C. Lini. The results presented support the suggestion that effective treatment of the seed may produce an increase of fibre not directly attributable to the prevention of seedling blight or stem break and browning but which may be explained by a general beneficial effect due to seed disinfection.
The results obtained suggest that no treatment consistently affected crop establishment in the field.     

Pre-sowing magnetic treatments of tomato seeds increase the growth and yield of plants

The effects of pre-sowing magnetic treatments on growth and yield of tomato (cv Campbell-28) were investigated under field conditions. Tomato seeds were exposed to full-wave rectified sinusoidal non-uniform magnetic fields (MFs) induced by an electromagnet at 100 mT (rms) for 10 min and at 170 mT (rms) for 3 min. Non-treated seeds were considered as controls. Plants were grown in experimental plots (30.2 m(2)) and were cultivated according to standard agricultural practices. During the vegetative and generative growth stages, samples were collected at regular intervals for growth rate analyses, and the resistance of plants to geminivirus and early blight was evaluated. At physiological maturity, the plants were harvested from each plot and the yield and yield parameters were determined. In the vegetative stage, the treatments led to a significant increase in leaf area, leaf dry weight, and specific leaf area (SLA) per plant. Also, the leaf, stem, and root relative growth rates of plants derived from magnetically treated seeds were greater than those shown by the control plants. In the generative stage, leaf area per plant and relative growth rates of fruits from plants from magnetically exposed seeds were greater than those of the control plant fruits. At fruit maturity stage, all magnetic treatments increased significantly (P < .05) the mean fruit weight, the fruit yield per plant, the fruit yield per area, and the equatorial diameter of fruits in comparison with the controls. At the end of the experiment, total dry matter was significantly higher for plants from magnetically treated seeds than that of the controls. A significant delay in the appearance of first symptoms of geminivirus and early blight and a reduced infection rate of early blight were observed in the plants from exposed seeds to MFs. Pre-sowing magnetic treatments would enhance the growth and yield of tomato crop.     

Take-all and grain yields in sequences of winter wheat crops testing fluquinconazole seed treatment applied in different combinations of years

A seed treatment containing fluquinconazole as the only active ingredient was tested in sequences of up to six consecutive crops of winter wheat. It was applied or not applied in each year, and was tested in all possible combinations with treatments applied in previous years. Take‐all was controlled effectively, and grain yield usually increased, when the disease intensity was moderate or severe in non‐treated crops, but control of the most severe take‐all did not result in acceptable yields or grain quality. Treatment of a first wheat or second wheat with little take‐all did not usually benefit the subsequent crop. Non‐treatment of a crop grown after a treated, diseased crop usually resulted in a marked increase in disease, indicating that treatment had delayed progress of the epidemic. Take‐all was controlled by treatment of a crop grown after a treated, diseased crop but the amount of control and of increased yield was often less than that in a treated crop grown after a non‐treated crop in the same crop sequence. Similar effects of seed treatment were apparent in crops grown on a site with take‐all decline. The alternative fungicide, silthiofam, applied as a seed treatment in the later years of some experiments, was usually as effective as fluquinconazole. From these experiments, it is recommended that: a) fluquinconazole seed treatment should be applied to a second or third wheat crop, grown after a first wheat crop that was managed to avoid rapid take‐all development (e.g. by avoiding very early sowing); b) a break crop should follow the treated crop; c) the seed treatment should not normally be used in longer sequences of wheat or on take‐all decline soil unless it is planned to follow the treated crop with a non‐cereal break.     

The effects of arbuscular mycorrhizal fungi and chitosan sprays on yield and late blight resistance in potato crops from microplants

The established microplants, mycorrhized and non-mycorrhized controls, were planted in the field and unsprayed (controls), sprayed with a conventional fungicide (Ridomil), with Ridomil alternating with N,O-carboxymethyl chitosan (NOCC — a soluble chitosan) or sprayed only with NOCC. The effects of the treatments on late blight progression in the crop were monitored throughout the season and yield measured. In a preliminary study on the inoculation of detached leaves from unsprayed plants and plants sprayed with Ridomil and NOCC, respectively, NOCC was shown to delay disease development. In the field, late blight development was most rapid in the unsprayed controls, delayed in the Ridomil-treated plants and disease progression was slowed in the other treatments (AMF-inoculation, AMF-NOCC sprayed, NOCC-sprayed and Ridomil-NOCC sprayed). It was shown that plant chitinase activity increased in the AMF, AMF-NOCC and NOCC treatments. At harvest, yields for the Ridomil-NOCC, NOCC and AMF-NOCC treatments were significantly higher than the un-sprayed, non-mycorrhizal control and were not significantly different to the Ridomil-sprayed control. The results are discussed in relation to the production of seed potatoes for organic (ecological) growers.     

The effect of Fusarium verticillioides on oviposition behaviour and bionomics of lepidopteran and coleopteran pests attacking the stem and cobs of maize in West Africa

Abstract The effect of Fusarium verticillioides Sacc. (Nirenberg) in maize stem and grain on the oviposition behaviour and bionomics of lepidopteran and coleopteran pests in West Africa was studied in olfactometer, greenhouse, and field trials in Benin. In a choice experiment, the pyralid Eldana saccharina (Walker) laid on average 31.9 eggs on inoculated maize stems vs. 9.2 and 7.8 on stems from plants, grown from hot‐water or fungicide treated seeds, respectively. For the pyralid Mussidia nigrivenella (Ragonot) the values were 42.1 in the inoculation and 7.8 eggs in the fungicide treatment. The survival of E. saccharina larvae was significantly higher from the inoculation than the hot‐water or fungicide treatments. Fecundity in the three treatments was 494, 307, and 268 eggs per female, respectively. In an olfactometer experiment, no significant differences were found in the time spent by the curculionid Sitophilus zeamais Motschulsky between the odor field with Fusarium‐infected grain and with uninfected grain, but both were significantly different from the controls. Significant differences were obtained for the nitidulid Carpophilus dimidiatus (Fabricius) with 50.5 and 35.8%, respectively, of the time spent in the Fusarium‐infected and non‐infected odor field. For both species, no differences were found between sexes. For S. zeamais, development time was significantly higher when reared on infected (37.2 days) than on non‐infected grain (34.4 days), whereas fecundity, expressed as number of progenies during the first 4 weeks, was lower on the inoculated grain (11 vs. 16 offspring per female). For C. dimidiatus the situation was the reverse: development time was shorter and fecundity was higher on infected grain (32.4 vs. 34.4 days, and 18 vs. 13 offspring per female, respectively). It was concluded that the higher pest densities found in the stem and ear of field grown maize was due to a higher attraction to and higher immature survival and adult fecundity on F. verticillioides infected plants.     

Integration of soil solarization with chemical, biological and cultural control for the management of soilborne diseases of vegetables

The long-term effectiveness of soil solarization integrated with (integration of pest management [IPM]) a biological control agent (Trichoderma virens), chemical fungicide (pentachloronitrobenzene [PCNB]), organic amendment (chicken litter) or physical method (black agriplastic mulch) to reduce southern blight (Sclerotium rolfsii) and southern root-knot diseases (Meloidogyne incognita) were evaluated on vegetable production. Results showed that the long-term effectiveness of IPM plus soil solarization reduced soilborne diseases of vegetables more than two years following the termination of solarization. These disease management strategies in 1991 and 1992, following soil solarization in 1990, reduced the numbers of sclerotia in the soil, and the number of plants killed by southern blight and root-knot of tomatoes, compared to nonsolarized bare soil treatment. The integration of a reduced dosage level of PCNB or T. virens in field plots, reduced southern blight of tomatoes by 100% and 71%, respectively, in solarized soil, compared to nonsolarized bare soil two years following soil solarization. PCNB effectively controlled southern blight in nonsolarized bare soil both years. All solarized treatments, except PCNB plus solarized soil increased tomato yields compared to nonsolarized bare soil plots. In the second study (1992) following soil solarization in 1991, the effectiveness of solarized bare soil, and nonsolarized bare soil mulched with black agriplastic film, with or without Reemay spunbounded polyester row cover, were effective in reducing root-knot of tomatoes as indicated by the root-knot gall index. Following a one year fallow period in 1994 three years following soil solarization, the root-knot gall index for severity of tomato roots grown in solarized bare soil, nonsolarized bare soil, black agriplastic mulched bare nonsolarized soil and black agriplastic mulched solarized bare soil, were 1.0, 3.0, 3.0 and 2.0, respectively, on a 0–5 scale, where 0=0% and 5=100% root-knot galled. In the third study 1992 and 1993, different dosage levels of chicken litter were used to amend soil artificially infested with sclerotia of S. rolfsii at different depths following solarization, decreased the number of viable sclerotia by 85–100%. All solarized treatments and nonsolarized bare soil amended with 18.8 MT/ha of chicken litter, were effective in controlling southern root-knot damage, and postharvest storage root rots of sweetpotato storage roots (Fusarium root rot [Fusarium solani] and Java black rot [Diplodia tubericola]). Our study showed that all soil solarization treatments, and soils amended with chicken litter, stimulated a shift in the soil microbial population dynamics. Rhizobacteria of Bacillus spp. and fluorescent pseudomonads increased significantly in the rhizosphere, rhizoplane, and interior root tissues of tomatoes and sweetpoatoes, grown in solarized soil compared to nonsolarized soil. These microorganisms may have contributed to the increased growth response of vegetables and some were probably suppressive to soilborne diseases     

Impact of seed-applied fungicide and insecticide on Azospirillum brasilense survival and wheat growth-promoting ability

The use of Azospirillum brasilense as a crop inoculant has increased in recent years. Thus, the compatibility of the inoculation technology with seed treatments using pesticides needs to be evaluated. In this study, we evaluated the effect of an insecticide and fungicide formulation on A. brasilense strain FP2 population by culturing and culture-independent approaches. In addition, we evaluated the impact of these pesticides on the ability of A. brasilense to promote plant growth by monitoring biometric traits (root and shoot dry mass and length) of wheat grown in Greenhouse conditions. Seed pesticide dressings, mainly fungicide, led to a significant mortality of A. brasilense over time. The ability of A. brasilense to promote wheat growth also decreased due to pesticide treatments combined with sowing delay. Considering that pesticides confer fitness advantages to the wheat in field condition, our results suggest that sowing within the first 4 h after inoculation maintain the beneficial effects of A. brasilense on wheat growth promotion. Furthermore, we conclude that inoculation and treatment of seeds with pesticides may be compatible techniques when carried out immediately before sowing.     

Growth promotion and root colonisation in pepper plants by phosphate‐solubilising Chryseobacterium sp. strain ISE14 that suppresses Phytophthora blight

Previously, we selected bacterial strain ISE14 through a sequential selection procedure that included radicle, seedling, and in planta assays and field tests. This strain not only suppressed a destructive soilborne disease, Phytophthora blight, caused by Phytophthora capsici but also increased fruit yields of pepper plants in the fields. This study was conducted to identify strain ISE14 by 16S rRNA gene sequence analysis and to characterise biocontrol and plant growth promotion activities of the strain in pepper plants. Strain ISE14, identified as Chryseobacterium sp., significantly reduced disease severity in plants inoculated with Ph. capsici and promoted plant growth (lengths and dry weights of shoots and roots) compared with those in plants treated with Escherichia coli DH5α (negative control) or MgSO₄ solution (untreated control). This strain effectively colonised pepper plant roots as assessed by bacterial population analysis and confocal laser scanning microscopy; it enhanced soil microbial activity and biofilm formation, but not the production of indole acetic acid. Strain ISE14 also solubilised organic or inorganic phosphate by production of acid and alkaline phosphatases or reduction in pH, resulting in enhanced pepper plant growth. This strain exhibited similar or greater activity in disease control and plant growth promotion tests compared with positive control strains Paenibacillus polymyxa AC‐1 (biocontrol) and Bacillus vallismortis EXTN‐1 (plant growth). Therefore, Chryseobacterium sp. ISE14 may be a phosphate‐solubilising and plant growth‐promoting rhizobacterium (PGPR) strain that suppresses Phytophthora blight of pepper. To our knowledge, this is the first report of a phosphate‐solubilising PGPR strain of Chryseobacterium sp. that suppresses the pepper disease.     

Suppression of southern corn leaf blight by a plant growth-promoting rhizobacterium Bacillus cereus C1L

Southern corn leaf blight (SCLB) is an important foliar disease of maize. In this study, an induced systemic resistance (ISR)-eliciting rhizobacterium Bacillus cereus C1L was used to protect maize against SCLB. Application of B. cereus C1L in maize rhizosphere effectively protected maize from SCLB under greenhouse and field conditions. The protection effect of B. cereus C1L was similar to that of Maneb (2 kg active ingredient per hectare), a recommended fungicide. Furthermore, possible factors of B. cereus C1L to elicit ISR and to promote plant growth were investigated. The results indicate that secreted factors and rhizosphere colonisation ability of B. cereus C1L are involved in ISR elicitation. In addition to biocontrol activity, B. cereus C1L was able to promote growth of maize in field. Compared with a non-treated control, leaf length, leaf width, plant height and fresh and dry weights of B. cereus C1L-treated corn plants significantly increased. Therefore, B. cereus C1L acts as a plant growth-promoting rhizobacterium of maize.     

Plant growth-promoting rhizobacterial mediated protection of tomato in the field against cucumber mosaic virus and its vector Aphis gossypii

Studies evaluated the effect of rhizobacterial interactions on a virus under natural conditions of high levels of vector–virus pressure on tomato plants. The rhizobacterium Bacillus subtilis was isolated from the rhizosphere soil of healthy tomato plant and the strain is referred to as BS3A25. The BS3A25 treatment of seeds significantly enhanced tomato seed germination rates to 99% compared to the control seeds at 78%. Combination of both seed and foliar spray treatments significantly protected the plants from cucumber mosaic virus (CMV) and also significantly enhanced plant growth. Strain BS3A25 possesses many positive traits such as phosphate solubilization ability, ACC utilization as the sole source of nitrogen and production of significantly higher concentrations of indoles, IAA and the cytokinin, IPA. The growth parameters of the aphid Aphis gossypii Glover such as development time, time from birth to adult (t_D) and prereproduction time (t_d) were longer, whereas the relative growth rate (RGR) and intrinsic rate of natural increase (r_m), were found to be lower in the BS3A25 supernatant treatment compared to commercial insecticide imidacloprid treatment. Noticeably, the present study recorded higher activity of phenylalanine ammonia lyase, Peroxidase, total phenols, and polyphenol oxidase in plants treated with BS3A25 generating the speculation of induced defence responses in plants. The results obtained in the field study showed that treatment by BS3A25 formulation as seed and foliar treatment proved highly effective in reducing the aphid population and CMV incidence compared to a commercially available insecticide. The highest cost:benefit ratio (1:2.5) was obtained in BS3A25 formulation treatment followed by imidacloprid (1:2.0) and control plants (1:1.4). These constitute an important step towards the production of BS3A25 as a commercially-available induced resistance agent.     

Biocontrol of tomato late blight with the combination of epiphytic antagonists and rhizobacteria

Control of tomato late blight (LB) in Brazil is heavily based on chemicals. However, reduction in fungicide usage is required in both conventional and organic production systems. Assuming that biological control is an alternative for LB management, 208 epiphytic microorganisms and 23 rhizobacteria (RB) were isolated from conventional and organically grown tomato plants and tested for antagonistic activity against Phytophthora infestans. Based on in vitro inhibition of sporangia germination and detached leaflet bioassays, four EP microorganisms (Aspergillus sp., Cellulomonas flavigena, Candida sp., and Cryptococcus sp.) were selected. These microorganisms were applied either singly or combined on tomato plants treated or not with the RB Bacillus cereus. On control plants, LB progress rate (r), area under disease progress curve, and final disease severity were high. Lowest values of final severity were recorded on plants colonized by B. cereus and treated with C. flavigena, Candida sp. and Cryptococcus sp. There was no reduction on disease severity in plants treated only with RB. Biological control of LB resulted in low values of r and final severity. Integration of biological control with fungicides, cultural practices, and other measures can contribute to manage LB on tomato production systems.     

Severed stems of Amaranthus palmeri are capable of regrowth and seed production in Gossypium hirsutum

Field studies were conducted to evaluate the capacity of Amaranthus palmeri to grow and reproduce following incomplete physical control in Gossypium hirsutum fields. A. palmeri plants that emerged simultaneously with a G. hirsutum crop were selected for use. Treatments included severing the main stem of flowering plants at heights of 0, 3 and 15 cm above the soil level. A non‐cut/intact control, in which the apical meristem was not removed, was also included. Six weeks after treatment, intact A. palmeri plants had grown to a mean height of 210 cm (SE = 38) and produced 477 408 (SE = 81 250) seeds per plant. Thirty‐five percent of the A. palmeri plants cut back to a height of 15 cm above the soil level did not recover from the treatment; survivors regrew to a mean height of 102 cm (51% reduction, compared to intact plants) and produced 116 000 seeds per plant (73% reduction). A. palmeri plants cut to 3 cm above the soil level had a mortality rate of 64%, an 82% reduction in final plant height, and produced 28 000 seeds per plant. When stems were severed at the soil surface, plant mortality was 95%; final plant height and seed production of survivors were reduced by 95 and 99%, respectively, relative to the control. G. hirsutum seeded yields exceeded 3 t ha^?1 when A. palmeri plants were cut back to at least 15 cm, whereas yield was reduced 50% in the control treatment, where A. palmeri growth was not interrupted by cutting. In conclusion, while there is immediate benefit of removing A. palmeri plants in terms of G. hirsutum yield, incomplete stem removal can have multi‐season implications. Results demonstrate that severely pruned A. palmeri plants can resume growth, reach reproductive maturity and produce viable seed, which have the potential to repopulate soil seedbanks.     

The effect of host plant species on performance and movement behaviour of the cabbage looper Trichoplusia ni and their potential influences on infection by Autographa californica multiple nucleopolyhedrovirus

• 1 Cabbage loopers Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) are serious pests in greenhouses growing tomatoes, cucumbers and bell peppers. A potential microbial control, now in development, is the broad host‐range virus Autographa californica multiple nucleopolyhedrovirus (AcMNPV).
• 2 The relationships between the three host plants and the feeding behaviour, larval movement and performance of cabbage looper larvae that might relate to their interaction with AcMNPV applications were investigated.
• 3 Larvae reared on cucumber plants consumed approximately ten‐fold more leaf area than larvae reared on pepper plants and almost five‐fold more than larvae reared on tomato plants. This could influence the amount of AcMNPV consumed if it were used as a microbial spray because increased consumption can be associated with increased probability of infection. Survival from neonate to pupa also varied, with the greatest being on cucumber, followed by tomato and pepper plants. Larvae fed cucumber were approximately four‐fold heavier than larvae fed tomato and over 15‐fold heavier than larvae fed pepper plants.
• 4 The distribution of larvae on plants in commercial greenhouses where a single crop was being grown also varied with food plant with 73% being found on the bottom and middle portions of tomato plants and 87% occurring in the top portions of pepper plants. Larvae tended to be distributed on the middle portion of cucumber plants, the lower portion of tomato plants and the top portion of pepper plants. Larval movement did not vary between AcMNPV‐infected and uninfected controls.
• 5 It is predicted that the higher leaf area consumption and location of larvae in the middle portion of cucumber plants may make them more susceptible to viral sprays. Furthermore, given their greater survival than larvae fed tomato and pepper, there may be a greater need for virus applications.

     

Pre‐dispersal seed predators and fungi differ in their effect on Luehea seemannii capsule development,seed germination,and dormancy across two Panamanian forests

Pre‐dispersal seed predation can greatly reduce crop size affecting recruitment success. In addition, non‐fatal damage by seed predators may allow infection by fungi responsible for post‐dispersal seed losses. The objectives of this study were (1) to quantify pre‐dispersal seed predation and fungal infection in a Neotropical tree species, Luehea seemannii, that produces dehiscent fruits and wind‐dispersed seeds, and (2) to link pre‐dispersal effects on seed quality to seed survival in the soil. To examine how seed predators and fungi influence seed losses, mesh exclosures, fungicide, and the combination of both treatments were applied to separate branches in the canopy of trees in Gamboa and Parque Natural Metropolitano (PNM), Panama. To determine if treatments affect seed viability and survival in the soil, half of the seeds collected from each treatment were buried for 4 weeks in forest soils and subsequently allowed to germinate before and after the breaking of dormancy. Overall, 24 percent of developing fruit were lost to insect attack. In contrast, fungi infected only 3 percent of seeds at the pre‐dispersal stage. For seeds germinated directly after collection, fungicide significantly increased germination in the wetter site (Gamboa) but decreased germination in the drier site (PNM). The pre‐dispersal insect exclosure treatment increased the fraction of seeds that remained dormant after burial in the soil. This result suggests that exposure to insect predators may cause physical damage to seeds that results in the loss of physical dormancy but does not necessarily increase the susceptibility of seeds to pathogen attack in the soil.     

Macromolecules Released by a Plant Growth-promoting Rhizobacterium as Elicitors of Systemic Resistance in Tomato to Bacterial and Fungal Pathogens

One of 500 rhizobacteria isolated from soil, rhizosphere and rhizoplane of healthy tomato plants was previously selected in laboratory, greenhouse and field tests as a good inducer of systemic resistance. This plant growth‐promoting rhizobacterium (PGPR) was identified as Bacillus cereus by fatty‐acid analysis. Bacillus cereus bacterial cells were removed from liquid culture by centrifugation and the supernatant repeatedly dialyzed (cut‐off = 12 000 daltons) against distilled water. Dialysates applied to roots protected tomato plants against leaf fungal and bacterial pathogens, evidence that macromolecules synthesized by the PGPR and released into the environment act as elicitors of systemic resistance.     

Transgenic Potatoes Expressing a Novel Cationic Peptide are Resistant to Late Blight and Pink Rot

Potato is the world's largest non-cereal crop. Potato late blight is a pandemic, foliar wasting potato disease caused by Phytophthora infestans, which has become highly virulent, fungicide resistant, and widely disseminated. Similarly, fungicide resistant isolates of Phytophthora erythroseptica, which causes pink rot, have also become an economic scourge of potato tubers. Thus, an alternate, cost effective strategy for disease control has become an international imperative. Here we describe a strategy for engineering potato plants exhibiting strong protection against these exceptionally virulent pathogens without deleterious effects on plant yield or vigor. The small, naturally occurring antimicrobial cationic peptide, temporin A, was N-terminally modified (MsrA3) and expressed in potato plants. MsrA3 conveyed strong resistance to late blight and pink rot phytopathogens in addition to the bacterial pathogen Erwinia carotovora. Transgenic tubers remained disease-free during storage for more than 2 years. These results provide a timely, sustainable, effective, and environmentally friendly means of control of potato diseases while simultaneously preventing storage losses.     

Stimulation of Armillaria mellea by phenolic fungicides

Phenolic fungicides, which were initially fungicidal to mycelium of Armillaria mellea on the surface of well‐colonised wood billets, eventually stimulated the growth of A. mellea. An extensive growth of rhizomorphs was produced from A. mellea inoculum, which had been exposed to phenolic chemicals for 3 months, compared to few or no rhizomorphs produced from inoculum exposed to water or a suspension of a non‐phenolic fungicide, fenpropidin. Inoculated privet plants grown either in pots or under field conditions were treated with a range of fungicides; fenpropidin, phenyl phenol, cresylic acid or water (control) was applied every 6 months over 21/2 yr. Fenpropidin caused a slightly (but significantly) lower incidence of infection than occurred in untreated plants, but the phenolic fungicides, cresylic acid and phenyl phenol, did not reduce the incidence of infection. The severity of infection (% root circumference colonised at 5 cm depth) was greater following cresylic acid treatments than the other fungicides or water‐treated controls. Use of phenolic fungicides such as cresylic acid for the control of A. mellea may therefore be counter‐productive.