The effect of carbendazim-generating fungicides with and without a mineral oil additive on tomato stem lesions caused by carbendazim-sensitive and tolerant strains of Botrytis cinerea

Isolates of Botrytis cinerea were obtained from tomatoes in several localities in the West Scotland. Some isolates grew on agar containing 100 mg/1 benomyl (carbendazim-tolerant), while others did not (carbendazim-sensitive). Pot-grown tomato plants treated with benomyl and other carbendazim-generating fungicides, applied either as sprays or soil drenches, were inoculated on the leaf scars with some of these isolates. On treated plants the carbendazim-tolerant isolates formed lesions which were about as large as those on untreated plants. Sensitive isolates formed much smaller lesions on treated plants. There was evidence that the increase in lesion size during the period 7–14 days after inoculation with a carbendazim-sensitive isolate was less on plants sprayed with benomyl or carbendazim with added mineral oil (2% Actipron) than on plants to which the fungicides alone had been applied. No such effect was recorded with thio-phanate-methyl. There was also an indication that the addition of Actipron to a benomyl spray improved the effect of the fungicide against two tolerant isolates, though there was no effect on the relative increase in lesion size during the second week after inoculation. In two tests the addition of 2% and 4% Actipron to benomyl soil drenches did not improve the level of leaf scar lesion control.     

Pathogenicity of benomyl-tolerant variants of Verticillium dahliae to strawberry, cv. Cambridge Vigour

Plants of cv. Cambridge Vigour were inoculated either with a benomyl-sensitive isolate of Verticillium dahliae or with one of two variants selected from it in vitro; these variants, Ri/8 and Ri/ii, were tolerant of benomyl at concentrations of 5 and 10 ppm respectively in the culture medium. The parent isolate and Ri/8 caused only mild wilt symptoms, but Ri/n was strongly pathogenic. A single treatment with benomyl (0–04 g/plant, in 100 ml water), applied as a soil drench o, 14, 29 or 57 days after inoculation, tended to reduce the mild symptoms caused by the parent isolate; the treatments had no apparent effect on Ri/8, but they slightly increased the severity of the wilt caused by Ri/n, especially after the earlier applications.     

The effect of Benlate and cytokinins on the content of tobacco mosaic virus in tomato leaf disks and cucumber mosaic virus in cucumber cotyledon disks and seedlings

Tomato leaf disks were inoculated with tobacco mosaic virus (TMV) and floated for 7 days on solutions of kinetin and benzyladenine in the range 20-0-002 mg/1. Virus content was reduced at the higher and increased at the lower concentrations. Benlate and benomyl showed a peak of cytokinin activity in the Amaranthus betacyanin bioassay equivalent to c. 0–002 fig/l kinetin. At concentrations above 25 and 100 mg a.i./l for Benlate and benomyl respectively, both compounds increased the TMV content of tomato leaf disks. Cucumber mosaic virus (CMV) content in cucumber cotyledon disks was increased by Benlate and benomyl treatment (50–100 mg/1). Applied as a soil drench (50–500 mg a.i./l) when the plants were inoculated, Benlate increased the CMV content of infected seedlings. The number of starch-iodide lesions (a measure of susceptibility) was unaltered in cotyledons treated with Benlate 7 days before or immediately after inoculation. Infectivity of crude infective cucumber sap was unaffected by benomyl incorporation, whereas Benlate reduced infectivity at higher concentrations (1000–5000 mg/1). Under the experimental conditions described, Benlate, benomyl, benzyladenine and kinetin had no effect on the chlorophyll content of tomato leaf disks, and intact seedlings.     

Effects of preplant inoculation of apple (Malus domestica Borkh.) with arbuscular mycorrhizal fungi on population growth of the root-lesion nematode,Pratylenchus penetrans

Six species of arbuscular mycorrhizal (AM) fungi (Glomus aggregatum, G. clarum, G. etunicatum, G. intraradices, G. mosseae and G. versiforme) were evaluated, in three greenhouse experiments, for their effects on reproduction of the root-lesion nematode, Pratylenchus penetrans, and growth of Ottawa 3 apple rootstock. Glomus mosseae increased total dry weights of nematode-inoculated and non-inoculated rootstock in all three greenhouse experiments, and G. intraradices increased dry weights in two of three greenhouse experiments. Plants inoculated with G. mosseae generally supported fewer P. penetrans per gram of root than plants inoculated with other AM fungi, but did not differ significantly from the controls in any greenhouse experiment. Colonization of roots by AM fungi was reduced by P. penetrans at initial inoculum densities greater than 250 nematodes/L soil. In field trials, preplant inoculation with either G. intraradices or G. mosseae increased rootstock growth and leaf concentrations of P, Mg, Zn and Cu in fumigated plots but not in non-fumigated plots, indicating that colonization by native AM fungi in non-fumigated plots may have been sufficient for adequate nutrient acquisition. The abundance of vesicles and arbuscules was greater in roots of plants inoculated with AM fungi before planting than in roots of non-inoculated plants, in both fumigated and non-fumigated plots. P. penetrans per gram of root and per 50 ml soil were significantly lower for G. mosseae- inoculated plants than for non-inoculated plants in fumigated soil but not in non-fumigated soil.     

Mycorrhizal colonization does not affect tolerance to defoliation of an annual herb in different light availability and soil fertility treatments but increases flower size in light-rich environments

Heterogeneous distribution of resources in most plant populations results in a mosaic of plant physiological responses tending to maximize plant fitness. This includes plant responses to trophic interactions such as herbivory and mycorrhizal symbiosis which are concurrent in most plants. We explored fitness costs of 50% manual defoliation and mycorrhizal inoculation in Datura stramonium at different light availability and soil fertility environments in a greenhouse experiment. Overall, we showed that non-inoculated and mycorrhiza-inoculated plants did not suffer from 50% manual defoliation in all the tested combinations of light availability and soil fertility treatments, while soil nutrients and light availability predominately affected plant responses to the mycorrhizal inoculation. Fifty percent defoliation had a direct negative effect on reproductive traits whereas mycorrhiza-inoculated plants produced larger flowers than non-inoculated plants when light was not a limiting factor. Although D. stramonium is a facultative selfing species, other investigations had shown clear advantages of cross-pollination in this species; therefore, the effects of mycorrhizal inoculation on flower size observed in this study open new lines of inquiry for our understanding of plant responses to trophic interactions. Also in this study, we detected shifts in the limiting resources affecting plant responses to trophic interactions.     

Mycorrhizal status of the endangered species Astragalus applegatei Peck as determined from a soil bioassay

 The mycorrhizal status of Astragalus applegatei Peck is reported for the first time on plants from a greenhouse soil bioassay. Seedlings were grown in a potting mix inoculated with soil collected near A. applegatei plants in nature. Plants were also grown in non-inoculated potting mix. Only plants from the native soil inoculation survived. Abundant colonization of VAM fungi was found in all 15 plants analyzed from the native soil treatment, and chlamydospores produced by Glomus spp. were observed. Mycorrhizal colonization was estimated to be 23% of total fine root length after 6 weeks and 53% after 14 weeks. Our results provide ecologically important information for conservation and restoration efforts underway to recover populations of this endangered species. Accepted: 22 June 1998     

Systemic action of benomyl against late-wilt disease of maize.

Benomyl (methyl-I-(butyl carbamoyl)-2-benzimidazole carbamate) at 2.5 to 100 ppm completely inhibited the growth in vitro of Cephalosporium maydis Samra, Sabet & Hingorani, the causal fungus of late-wilt of maize. In pot experiments, late-wilt was controlled by applications equivalent to 10 ppm benomyl/unit wt dry soil at sowing but not by applications 30 days after sowing or by seed treatments (dusts and dips). A fungitoxic substance was detected in benomyl-treated soil, planted with maize, 120–150 days after treatment and for 150–180 days in unplanted soil. Sap expressed from maize grown in benomyl-treated soil was also fungitoxic, especially that from the roots and distal parts of the leaf blades. In the field, soil applications of benomyl to 10 kg/feddan (4200 m²) failed to control late-wilt. Tests indicated little fungitoxicity in the sap of maize plants 25 days after sowing.     

Root Rot and Wilt of Kangaroo Paw (Anigozanthos manglesii) Caused by Pythium myriotylum (Drechs.) in Israel

A root rot and wilt disease of Anigozanthos manglesii (Kangaroo Paw) grown in greenhouses in Israel, for exporting as cut flowers to Europe, was characterized. Pythium myriotylum (Drechs.) and Rhizoctonia solani (Kühn) were the prevalent pathogens in diseased plants collected from commercial greenhouses. Fusarium oxysporum, Fusarium spp. and Myrothecium sp. were also isolated, but P. myriotylum or R. solani were not detected in samples from symptomless plants in tissue cultures (Australian origin) or plants at different stages in the nursery; non‐pathogenic F. oxysporum and Fusarium spp. were detected in several samples. In pathogenicity tests carried out in pots, plant mortality occurred 7 days after inoculation with P. myriotylum. In a field experiment carried out in methyl bromide‐fumigated soil, the incidence of dead plants following inoculation with P. myriotylum alone was 22% 10 days after inoculation, increasing to 78% after an additional 25 days. The incidence of dead plants following inoculation with R. solani alone was only 5% and in plants inoculated simultaneously with both pathogens, disease incidence was 88% 35 days after inoculation. Mortality reached 90–100% in plants inoculated with P. myriotylum, either singly or combined with R. solani 60 days after inoculation, whereas in plants inoculated with R. solani it was 5%. The maximum mortality in plants inoculated with R. solani was 25%, 76 days after inoculation. These results clearly demonstrate that P. myriotylum was the dominant pathogen in the root rot and wilt of A. manglesii.     

The effect of benomyl on the infection of tomatoes by Fusarium oxysporum f.sp. lycopersici and Botrytis cinerea

In glasshouse experiments at Auchincruive, drench applications of benomyl (100 or 142 mg per plant) to the soil surface around the stem bases of pot-grown tomato plants before inoculation with Fusarium oxysporum f.sp. lycopersici reduced the penetration of the fungus up the stems and/or decreased the development of vascular discoloration and associated severity of wilting. Similar drenches applied after establishment of the fungus in the stems either halted or considerably retarded the growth of the pathogen up the vessels. This again was reflected in reduced vascular discoloration and wilt symptoms. In experiments with benomyl over 2 years at a commercial holding in Argyll, the application of soil drenches (at the rates above) shortly after planting out and again 5 weeks later, coupled with a programme of stem and foliar sprays (at 0–05 % a.i.) during the summer, reduced the development of stem lesions caused chiefly by Botrytis cinerea and increased the general survival of plants more than did drench or spray treatments alone. There were indications that ‘ghost spotting’ of the fruit, particularly where spray applications were made, was also slightly reduced, but the magnitude of the effect was not consistent.     

Arbuscular mycorrhiza‐mediated resistance in tomato against Cladosporium fulvum‐induced mould disease

Root colonization with arbuscular mycorrhizal fungi (AMF) enhances plant resistance particularly against soil‐borne pathogenic fungi. In this study, mycorrhizal inoculation with Glomus mosseae (Gm) significantly alleviated tomato mould disease caused by the air‐borne fungal pathogen, Cladosporium fulvum (Cf). The disease index (DI) in local leaves (receiving pathogen inoculation) and systemic leaves (just above the local leaf without pathogen inoculation) was 36.4% and 11.7% in mycorrhizal plants, respectively, whereas DI was 59.6% and 36.4% in the corresponding leaves of AMF non‐inoculated plants, after 50 days of Gm inoculation, corresponding to 15 days after Cf inoculation by leaf infiltration. Foliar spray inoculation with Cf also revealed that AMF pre‐inoculated plants had a higher resistance against subsequent pathogen infection, where the DI was 41.3% in mycorrhizal plants vs. 64.4% in AMF non‐inoculated plants. AMF‐inoculated plants showed significantly higher fresh and dry weight than non‐inoculated plants under both control (without pathogen) and pathogen treatments. AMF‐inoculated plants exhibited significant increases in activities of superoxide dismutase and peroxidase, along with decreases in levels of H₂O₂ and malondialdehyde, compared with non‐inoculated plants after pathogen inoculation. AMF inoculation led to increases in total chlorophyll contents and net photosynthesis rate as compared with non‐inoculated plants under control and pathogen infection. Pathogen infection on AMF non‐inoculated plants led to decreases in chlorophyll fluorescence parameters. However, pathogen infection did not affect these parameters in mycorrhizal plants. Taken together, these results indicate that AMF colonization may play an important role in plant resistance against air‐borne pathogen infection by maintaining redox poise and photosynthetic activity.     

Enhancement of the efficiency of Cd phytoextraction using bacterial endophytes isolated from Chromolaena odorata,a Cd hyperaccumulator

Phytoextraction is a technique using a hyperaccumulator to remove heavy metals from soil. The efficiency of heavy metal uptake can be enhanced by the inoculation of endophytes. In this study, we isolated and identified 23 endophytes from Chromolaena odorata, a cadmium (Cd) hyperaccumulator that consisted of 19 bacteria, 2 actinomycetes and 2 fungi. All bacteria and fungi could produce at least 1 plant growth promoting factors. However, only 4 bacterial isolates; Paenibacillus sp. SB12, Bacillus sp. SB31, Bacillus sp. LB51, and Alcaligenes sp. RB54 showed the highest minimum inhibitory concentration (MIC) value (2.9 mM), followed by Exiguobacterium sp.RB51 (1.7 mM). Then, these 5 high-MIC bacteria and 1 low-MIC bacterium, Bacillus sp. LB15 were inoculated onto sunflower grown in soil supplemented with 250 mg/kg of Cd. After 60 days, all inoculated plants accumulated significantly higher Cd concentration than the non-inoculated counterparts, and those inoculated with strain LB51 showed the highest Cd accumulation and growth. Interestingly, strain LB15 with low MIC also enhanced Cd accumulation in plants. The results suggest that these bacteria, particularly strain LB51, could be applied to improve Cd accumulation in plants, and that bacteria with low MIC also have the potential to enhance the efficiency of phytoextraction.     

Cyanobacterial inoculation and nitrogen fertilization in rice

During three rice-growing seasons in Uruguay, field experiments were conducted to study the contribution of cyanobacterial inoculation and chemical N fertilization to rice production. Neither grain yield nor fertilizer recovery by the plant were affected by inoculation with native cyanobacterial isolates. A low fertilizer use efficiency (around 20%) was observed when labelled (NH₄)₂SO₄ was applied at sowing. Recovery of applied ¹⁵N by the soil–plant system was 50%. Inoculation did not modify ¹⁵N uptake by the plant when the fertilizer was three-split applied either. The total N-fertilizer recovery was higher when the fertilizer was split than when applied in a single dose. Plant N-fertilizer uptake was higher when the fertilizer was applied at tillering. Uptake of ¹⁵N from cyanobacteria by rice was studied in a greenhouse pots experiment without chemical nitrogen addition. Recovery of ¹⁵N from labelled cyanobacteria by rice in greenhouse growth conditions was similar to that of partial recovery of (NH₄)₂SO₄ applied at sowing in the field. Cyanobacterial N mineralization under controlled conditions was fast as cyanobacterial N was detected in plants after 25 days. Moreover 40 days after inoculation non-planted and inoculated soil had more inorganic N than the non-inoculated one.     

Effects of pH on NaCl tolerance of American elm (<Emphasis Type="Italic">Ulmus americana</Emphasis>) seedlings inoculated with <Emphasis Type="Italic">Hebeloma crustuliniforme</Emphasis> and <Emphasis Type="Italic">Laccaria bicolor</Emphasis>

In the present study, we investigated the effects of pH treatments on NaCl tolerance in mycorrhizal and non-mycorrhizal American elm. American elm (Ulmus americana) seedlings were inoculated with Hebeloma crustuliniforme, Laccaria bicolor or with both mycorrhizal fungi and subsequently subjected to different pH solutions (pH 3, 6 and 9) containing 0 mM (control) and 60 mM NaCl for 4 weeks. Inoculation with the mycorrhizal fungi did not have a large effect on seedling dry weights when the pH and NaCl treatments were considered independently. However, when the inoculated seedlings were treated with 60 mM NaCl at pH 3 or 6, shoot to root ratios and root hydraulic conductivity were higher compared with non-inoculated plants, likely reflecting changes in seedling water flow properties. At pH 6, transpiration rates were about twofold lower in non-inoculated plants treated with NaCl compared with non-treated controls. For NaCl-treated H. crustuliniforme- and L. bicolor-inoculated plants, the greatest reduction of transpiration rates was at pH 9. Treatment with 60 mM NaCl reduced leaf chlorophyll concentrations more in non-inoculated compared with inoculated plants, with the greatest, twofold, decrease occurring at pH 6. At pH 3, root Na concentrations were higher in inoculated than non-inoculated seedlings; however, there was no effect of inoculation on root Na concentrations at pH 6 and 9. Contrary to the roots, the leaves of inoculated plants had lower Na concentrations at pH 6 and 9, but not at pH 3. The results point to an interaction between ECM fungi and root zone pH for salt tolerance of American elm.     

Variation in the Essential Oil Composition,Antioxidant Capacity,and Physiological Characteristics of Pelargonium graveolens L. Inoculated with Two Species of Mycorrhizal Fungi Under Water Deficit Conditions

In recent years, the application of arbuscular mycorrhizal fungi (AMF) has been considered to be an important strategy for improving crop yield and quality. In the present study, a factorial experiment based on a complete randomized design with two factors was performed to investigate the effect of AMF and water stress on the essential oil (EO) composition, antioxidant activity, and physiological and morphological characteristics of rose-scented geranium (Pelargonium graveolens L.). The factors included AMF inoculation (Rhizophagus intraradices, Funneliformis mosseae, and a mixture of both species) and irrigation levels [well-watered (WW), moderate drought stress (MDS), and severe drought stress (SDS)]. The main EO constituents were citronellol (31–37%) and geraniol (9–14%) in all treatments. Under water-stress conditions, some constituents increased, such as geraniol and geranyl formate, whereas others decreased, such as linalool, menthone and rose oxide. Overall, the highest amount of citronellol (37.3%) and geraniol (14.8%) was obtained in the plants inoculated with F. mosseae and R. intraradices under WW and MDS conditions, respectively. Antioxidant activity, total flavonoids, and phenolics were increased because of AMF inoculation, whereas a different trend was observed for the phenolic and flavonoid contents under water-stress conditions. Furthermore, water deficit elevated the amount of soluble carbohydrates as well as the proline content, whereas the amount of proline was lower in inoculated plants than in non-inoculated ones. All the growth parameters were improved in the AMF-inoculated plants compared to non-inoculated ones under different irrigation regimes. Drought conditions decreased the photosynthetic pigments and efficiency, whereas AMF plants ameliorated the adverse effect of drought conditions. In general, mycorrhizal inoculation resulted in an improvement in the growth parameters as well as the phytochemical and physiological characteristics of rose-scented geranium.

     

Systemic fungicides in the control of strawberry wilt (Verticillium dahliae)

In a series of experiments between 1970 and 1973 the application of benomyl or thiophanate methyl to field-grown strawberries, planted on Verticillium-mtested land, gave control of wilt for up to 5 months, the duration of control being related to the amount of fungicide applied in the spring. Treatment of inoculated plants grown on in chloropicrin-fumigated soil was effective for at least two seasons. An autumn-planted multi-factorial experiment in heavily-infested soil showed that, to achieve maximum wilt control, it was advantageous to grow cv. Gorella rather than cv. Cambridge Vigour; to drench the runners at planting rather than to dip them in the fungicide suspension; and to use a high concentration (0–075 % a-i-) and large volume (600 ml per plant) for a supplementary treatment in May rather than a lower concentration (0.025 %) ^or smaller volume (400 ml). There were small but significant advantages in applying benomyl rather than thiophanate methyl, and in using 0–2% a.i. suspension at planting rather than 0–05%. No advantage was gained by dividing the spring application into two equal doses applied 2 wk apart. Extrapolation from the logarithmic relation between wilt index and total dose of fungicide applied in the spring suggested that I.I g/plant would have given almost complete control until October; such control had been achieved in an earlier experiment in which 1–2 g/plant was applied. Crop yield in the second year was determined by the treatment applied in the first year, but although these treatments had given significantly better control of wilt in Gorella than in Cambridge Vigour, the greater growth and yield potentials of the latter cultivar had an over-riding effect on crop production; Cambridge Vigour yielded more than Gorella under all chemical treatments, but in the absence of treatment Gorella gave a larger crop than Cambridge Vigour. A proposed regime, entailing spring and autumn applications, is aimed at minimizing the colonization of the plant throughout the year, thus reducing the production of new inoculum and, by limiting the quantity of the pathogen in contact with the systemic chemicals, minimizing the probability of selecting fungicide-resistant variants of V. dahliae.     

Response of onion plants to arbuscular mycorrhizae

Onion (Allium cepa) plants were grown in pots in two types of irradiated soil, mineral and organic. Onion development was observed under two or three levels of P fertilization, and three methods of arbuscular mycorrhizal fungus inoculation with two fungus species. In mineral soil, preinoculated onion plants had a higher biomass than non-inoculated control plants or plants inoculated with either colonized root segments or spores. Fungus species had no differential effect on dry biomass or final bulb diameter. Preinoculated onion plants reached marketable size (>25 mm bulb diameter) 2-3 weeks earlier than those inoculated by either of the other two methods. Non-inoculated onion plants remained stunted. Bulbs of onions inoculated with Glomus versiforme were firmer than those inoculated with G. intraradices. Increasing P fertilizer rates had a significant positive linear effect on the P tissue concentration of plants inoculated with G. intraradices or G. versiforme, but no effect on bulb firmness. The P tissue concentration of inoculated plants was significantly higher than that of non-inoculated controls, and in inoculated plants, it differed among inoculation methods. The P tissue concentration was higher in onion plants inoculated with G. versiforme than in those inoculated with G. intraradices. In organic soil, the dry biomass of preinoculated plants was higher than that of plants inoculated by root segments. The highest root colonization levels were obtained under a low soil P level with G. intraradices, and with the root segment method of inoculation with G. versiforme.     

Evaluation of fungicides for the control of Verticillium wilt (V. dahliae) of strawberry

The treatment of soil or plants before planting, in September 1969, significantly reduced Verticillium wilt on strawberry in the following season. One application of benomyl or thiabendazole (both 0–5% a.i.) at 6728 l/ha to soil 24 h before planting, dusting roots with formulated benomyl powder (50% a.i.) at planting, or a combination of both benomyl dust + drench treatments were effective. However, although the double treatment gave the most disease control in 1970, plants from the soil-drench treatments gave the highest yields. Residual effects of the 1969 applications were still evident in 1971 from increased vigour, lack of wilt and high yield, especially with the benomyl treatments.     

Factors affecting aphid acquisition and transmission of soybean mosaic virus

Myzus persicae transmitted soybean mosaic virus (SMV) most efficiently following 30 or 60 s acquisition probes on infected plants. There were no differences in susceptibility to SMV infection of soybean plants 1 to 12 wk old, but symptoms were more severe in plants inoculated when young than when old. Soybeans inoculated between developmental stages R3 and R6 only showed yellowish-brown blotching on one or more leaves. There were no observable differences in the time of appearance or type of symptoms shown by soybean seedlings inoculated either by sap or by aphids; infected plants became acquisition hosts for aphids 5–6 days after inoculation. There was no change in the efficiency with which M. persicae transmitted SMV from source plants up to 18 wk after inoculation. M. persicae transmitted SMV from leaves of field-grown soybeans when plants were inoculated at developmental stages V6, R2, and R3 and tested as sources 57–74 days after inoculation but not from plants inoculated at R5 and tested as sources 14 to 32 days after inoculation. M. persicae acquired SMV from soybean buds, flowers, green bean pods, and unifoliolate, trifoliolate, and senescent leaves. Middle-aged and deformed leaves were better sources of the virus than buds, unfolding and old symptomless leaves. The results are being incorporated into a computer model of SMV epidemiology.