Formation Of Infection Cushions Research Articles

A nonpathogenic species of binucleate Rhizoctonia inhibits the formation of infection structures caused by Rhizoctonia solani on cucumber

Binucleate Rhizoctonia (BNR) W7 was evaluated for the efficacy to control damping-off disease in cucumber seedlings. Results revealed that Lobate appresoria and dome-shaped infection cushion were produced by virulent Rhizoctonia solani C9 AG4 on the surface of the cucumber seedling hypocotyls, causing damping-off, 12 h after inoculation. A significant positive correlation was observed between disease severity rating and number of infection cushions (r = 0.94) and appresoria (r = 0.97) on the hypocotyls of seedlings inoculated with virulent R. solani C9 alone. Inoculation of a nonpathogenic species of BNR prior to virulent R. solani significantly reduced the number of appresoria on hypocotyls surface and inhibited the formation of infection cushions that accompanied by highly significant (P ≤ 0.01) reduction in disease severity in comparison with seedling inoculated with R. solani C9 alone. Formation of mucilaginous material upon recognition of the nonpathogenic isolate of BNR followed by hyphal lysis of BNR W7 6 h after inoculation was responsible for reduction in appresorium formation and complete inhibition of infection cushion formation. However, the number of infection structures produced on cucumber was not significantly different for hypocotyls of seedlings inoculated with R. solani C9 with and without the nonpathogenic BNR W7.

Inhibitory efficacy of endophytic Bacillus subtilis EDR4 against Sclerotinia sclerotiorum on rapeseed

Stem rot, caused by Sclerotinia sclerotiorum, is a serious disease of rapeseed worldwide. This paper tested the inhibitory effect of an endophytic bacterial Bacillus subtilis strain, EDR4, on the sclerotial germination and hyphal growth of S. sclerotiorum. The cell-free filtrate solution and cell suspension of strain EDR4 were sprayed on rapeseed leaves and stems one day before, at the same time and one day after inoculation in the greenhouse experiments. There was no significant difference in inhibitory efficacy between the cell-free filtrate solution and cell suspension. The best biocontrol efficacy was achieved by spraying either the cell-free filtrate solution or cell suspension at the same time as inoculation. In the field trials, the efficacy of two applications of EDR4 cell suspension at the initial flowering stage and full bloom stage was the best, but there was no significant difference in efficacy between the one-application and two-application treatments during the initial flowering stage. The efficacy decreased gradually with the culture suspension dilutions. Scanning electron microscopy revealed that EDR4 cells significantly suppressed the hyphal growth. The bacterial treatment caused shrink, cytoplasm leakage and irregular tip swelling of fungal hyphae. The hyphal cells in the treated groups had higher numbers of vacuoles in the cytoplasm than the non-treated hyphal cells. The hyphal cytoplasm was disintegrated; the hyphal biomass was reduced; the formation of infection cushions was delayed; and the infection was suppressed after spraying the bacterial culture on rapeseed leaves. The results showed that the EDR4 bacterial strain could be used to control stem rot of rapeseed.

Effect of Mitovirus infection on formation of infection cushions and virulence of Botrytis cinerea

This study was conducted to investigate mechanisms involved in hypovirulence of strain CanBc-1 of Botrytis cinerea. The hypovirulent strain CanBc-1 was compared with the virulent strains CanBc-1c-66 and CanBc-2 of B. cinerea for formation of infection cushions on onion bulbs and on leaves of oilseed rape and tomato, as well as for production of pectinase, toxic metabolites, oxalic acid and laccase in different growth media. Results showed that formation of infection cushions was common on epidermis of onion bulbs and on leaves of oilseed rape and tomato inoculated with strains CanBc-1c-66 or CanBc-2, but was rare on these plant tissues inoculated with strain CanBc-1. The three strains could produce pectinase, toxic metabolites, oxalic acid and laccase in pure cultures. Strain CanBc-1 produced less pectinase in 9-day-old cultures in pectin-containing liquid medium than strains CanBc-1c-66 and CanBc-2. The yield of oxalic acid (OA) produced by strain CanBc-1 in 15-day-old cultures in Maxwell liquid medium was lower than that produced by strain CanBc-2, but was higher than that produced by strain CanBc-1c-66. Strain CanBc-1 produced more laccase than strains CanBc-1c-66 and CanBc-2 in 8-day-old cultures in potato dextrose broth (PDB). Cultural filtrates of strains CanBc-1, CanBc-1c-66 and CanBc-2 from 21-day-old PDB cultures suppressed growth of roots and hypocotyls of barley, and the suppressive efficacy was not significantly different ( P > 0.05) among the three investigated strains of B. cinerea. These results suggest that rare formation of infection cushions and attenuated mycelial growth are probably responsible for hypovirulence of strain CanBc-1 of B. cinerea infected by the mitovirus BcMV1.

A Root Box Method to Estimate Virulence of Helicobasidium mompa Using Carrots and Its Comparison with the Conventional Method Using Apple Stocks

A root box method with carrots was developed to estimate virulence of the violet root rot fungus, Helicobasidium mompa, to facilitate short-term screening of many isolates during a year. The root box consisted of two transparent acrylic plates and a plastic bag of vermiculite in which two taproots of carrot were growing and inoculated with the fungus growing on fragments of mulberry twigs. The boxes were kept in a greenhouse at 25°C, and the surface of carrots was observed weekly up to 14 weeks. The virulence of each isolate was determined based on the number of weeks after inoculation required for the fungus to develop infection cushions on the surface of carrots. Results were compared with those from the conventional inoculation method using apple stocks. Two-year-old 456 apple stocks were planted with or without fungal inoculum in 30-cm diam. plastic pots containing commercial soil and placed outdoors in April 1999. Symptoms on plant tops were observed weekly, and the first stocks were killed 14 weeks after inoculation. At the end of trial 1 (6 months) and trial 2 (14 months), apple stocks were dug up to rate disease index (DI) based on hyphal growth and infection cushion formation on the stem base. There was variability in disease severity among replicates as well as isolate variability ; however, the results were similar in both trails. The level of virulence estimated by both methods was almost parallel for a total of 23 isolates from five plant species, except for two isolates from sweet potato that formed no obvious infection cushion on apple roots but on carrot were the most virulent.

Infection of alfalfa pollen bySclerotinia sclerotiorum

Blossom blight, caused bySclerotinia sclerotiorum, has become an important disease of alfalfa (Medicago sativa L.) in seed production areas of western Canada. Studies using light microscopy and scanning and transmission electron microscopy revealed that pollen grains of alfalfa are susceptible to infection byS. sclerotiorum. Ascospores ofS. sclerotiorum germinated readily in water with or without pollen grains. Examinations of ascospore—pollen mixtures incubated at room temperature (20–22°C) for 5 days revealed that numerous pollen grains were infected byS. sclerotiorum by direct hyphal penetration through the equatorial germinative pores or through the exine and intine layers of the pollen wall without the formation of infection cushions or appressoria. After penetration, hyphae ramified within the pollen grains, causing plasmolysis of the cytoplasmic membrane and eventual disintegration of the pollen cytoplasm. The study suggests that alfalfa pollen may play a role in the epidemiology of blossom blight in alfalfa.

Factors affecting infection cushion development by Rhizoctonia solani AG‐1 IA and IB on soybean leaves

Infection cushions were formed by isolates of Rhizoctonia solani, anastomosis group 1 IA (AG‐1 IA, aerial blight) and AG‐1 IB (web blight) on leaves of all 10 soybean cultivars tested. Isolates of AG‐1 IA and IB did not form infection cushions on soybean leaf surface replicas of either resistant or susceptible cultivars. More infection cushions were formed by isolates of AG‐1 IA and IB on collodion membranes placed over leaves of susceptible cultivars compared with resistant cultivars. Isolates of AG‐1 IC. AG‐4 and AG‐5, also formed infection cushions on soybean leaves. However, the isolates of other anastomosis groups did not form infection cushions on soybean leaves. Differential induction of infection cushion formation by the leaves of various plant species was observed, AG‐1 IA formed infection cushions on more graminaceous hosts than AG‐1 IB, Our results suggest that a chemical stimulus is needed for infection cushion formation. Glucose and 3‐O‐methylglucose repressed disease severity caused by AG‐1 IA and IB isolates to the same extent. Disease severity and the number of infection cushions formed on leaves of ten soybean cultivars were correlated. Fewer infection cushions were formed on resistant cultivars than on susceptible cultivars.

Development of a Systemic Fungicide, Flutolanil

In the course of our research work for a novel systemic fungicide to control rice sheath blight disease caused by Rhizoctonia solani, various derivatives having amide linkage, especially benzanilide derivatives were synthesized for biological screening. Trifluoromethyl at the ortho position of the acid moiety of benzanilide was selected as the most favorable substituent with a certain level of steric bulk and lipoid solubility. Alkoxy groups introduced at the meta position of the aniline moiety enhanced the fungitoxic activity. Ultimately, flutolanil (α, α, α-trifluoro-3′-isopropoxy-2-toluanilide) was selected as the most potent compound for our purpose. Flutolanil is the first registered fungicide able to control rice sheath blight with application of granules into paddy water as well as foliar spray application in Japan. Approximately 2ppm of flutolanil in rice leaf sheaths contributed to about 80% suppression of the disease development by inhibiting hyphal growth, infection-cushion formation and penetration from infection cushion of R. solani on leaf sheaths. In paddy fields, flutolanil showed the best performance when applied into paddy water during the horizontal development of the disease or when applied as a foliar spray once or twice at appropriate timing. Biochemical mode of action of flutolanil seems to be inhibition of a succinate dehydrogenase complex, an important enzyme complex in the respiratory chain of basidiomycetous fungi but not of fungi in other classes. Toxicological and metabolic studies revealed the character of flutolanil highly safe to mammalians and environment.

Resistance of narcissus to infection by Fusarium oxysporum f.sp. narcissi

Single hyphae of Fusarium oxysporum f.sp. narcissi were capable of direct penetration of intact, unwounded, root tips of the susceptible narcissus cv. Golden Harvest. In other parts of the root, penetration involved the formation of infection cushions. In general, advance of the fungus in roots was by inter- and intracellular growth. In bulb scales spread occurred via ducts prior to invasion of surrounding tissue. In roots of the resistant cv. St Keverne, epidermal cell walls were modified in the presence of the fungus and lignituber-like structures were deposited about invading hyphae. Such structures were not produced in root cap cells. Isolated bulb scales expressed differential resistance to F. oxysporum f.sp. narcissi, indicating that a significant part of the resistance of cv. St Keverne has a physiological basis. The accumulation of antifungal compounds, including 7-hydroxyflavan and 7,4′-dyhydroxy-8-methyflavan, was compared in bulb scales of Golden Harvest and St Keverne following wounding or inoculation with the pathogen. It was concluded that resistance involves a complex interaction between the accumulation of antifungal compounds following infection, cell wall modification, and the formation of lignituber-like structures.

The Role of the Cuticle in Resistance of Beans toRhizoctonia solani

Stockwell, V., and Hanchey, P. 1984. The role of the cuticle in resistance of beans to Rhizoctonia solani. Phytopathology 74:1640-1642. The resistance of 3-wk-old Red Kidney bean plants to Rhizoctoniasolani they became permeable to dyes. After inoculation, the fungus is associated with the inability of the fungus to form infection cushions and formed infection cushions and lesions on these treated older plants s milar penetrate the hypocotyl. Two factors suggested to be important in this to those formed on young plants. Simple infection cushions were more resistance are increased calcification of cell walls and increased cuticle common on treated older plants, whereas complex infection cushions thickness. Cuticle permeability of hypocotyls of 1-and 3-wk-old seedlings predominated on young seedlings. The ability of the fungus to form was determined by immersing them in dyes. Dyes penetrated the cuticle of infection cushions on older, more calcified plants after the cuticle has been the younger, but not the older, plants. When hypocotyls of 3-wk-old plants altered suggests that cuticle thickness plays a more important role than were rubbed with cotton wetted with water or chloroform, gently abraded calcification of cell walls in the resistance of older plants to R. solani. with Carborundum, rinsed with chloroform, or grown in a mist chamber, Additional key word: Phaseolus vulgaris. The susceptibility of bean seedling hypocotyls to Rhizoctonia removal on resistance, hypocotyls of I- or 3-wk-old plants were solani KUhn decreases until they are about 3 wk old. Two treated by one of the following methods, then rinsed with distilled explanations have been proposed for this phenomenon. Bateman water and inoculated as described above. Control plants were and Lumsden (2) found a higher calcium content in older rinsed with distilled water. Hypocotyls of some plants were ru bed hypocotyls. These data, together with the observation that walls three times with cotton (on an orangewood stick) moistened with from older plants are less readily macerated by fungal either distilledwaterorchloroform. Thehypocotylsurfaceof other endopolygalacturonase, led to the hypothesis that the pathogen plants was gently abraded with Carborundum. To avoid physical was unable to macerate calcified walls of older hypocotyls and effects (such as surface topography changes) associated with cause lesions. Others suggested that resistance of radish, rubbing, stems were rinsed with 1 ml of chloroform or the plants groundnut, and cotton to Rhizoctonia is determined prior to were grown in a mist chamber (90% RH, 25 C) for 3 wk, to retard penetration and is associated with the inability of the pathogen to cuticle development. After treatment, hypocotyls were exanmined form infection cushions (6,12,16). Infection cushion formation under fluorescence microscopy for changes in cuticular apparently requires exudates (8) which are reduced by the thicker autofluorescence. Fresh cross sections of hypocotyls were mo nted cuticle of older plants (12). Thus, older bean plants may be resistant in distilled water on a glass slide and examined with an Olympus because the quantities of the exudates are insufficient to stimulate BMF fluorescent microscope with two OG-I 2 excitation filter and infection cushion formation. a 515-nm barrier filter. Stockwell and Hanchey (14) confirmed by chemical analysis and Staining with methylene blue or neutral red. Staining with ultrastructural histochemistry that the calcium content of methylene blue or neutral red was used to determine the relative hypocotyl walls increases with age. Additionally, we found that permeability of the cuticle to dyes. Bean plants, 1 or 3 wk old, cuticle thickness was greater on older hypocotyls. untreated or treated as described in the previous section, were The purpose of the present research was to determine the role of gently removed from soil, rinsed, and immersed in either 0.1% the cuticle in resistance of older bean hypocotyls to R. solani. (w/v) neutral red or 0. 1% (w/v) methylene blue for 10 min. Upon removal from the dye, plants were rinsed with distilled water, and

Infection of plants by Corticium solani and C. praticola—Effect of plant exudates

The parasitism by two strains of Corticium solani (Prill. & Delacr.) Bourd. & Galz. and one of C. praticola Kotila has been investigated. A lettuce strain of C. solani parasitized lettuce but not cabbage: a cabbage strain parasitized cabbage but not lettuce. C. praticola parasitized both. Wheat was not parasitized by the strains of C. solani but was parasitized to a limited extent by C. praticola . Exudates from the roots of cabbage seedlings stimulated the growth of each of the three fungi to the same extent. Exudates from lettuce seedling roots also did this but the effects were much more striking. Wheat root exudates had very little effect on the growth of either of the fungi. These results refute the hypothesis that exudates are an important factor in the specificity of parasitism of different strains of C. solani . When exudates from roots of different ages were examined it was found that those secreted in the first week after sowing seed were much more effective than those secreted in the second and third weeks. Root exudates did not stimulate the formation of infection cushions on pieces of epidermis from different host plants in any way that could be correlated with specificity of parasitism. But infection cushions were formed much more abundantly on pieces of epidermis taken from susceptible as compared with resistant plants. In general the cushions formed on epidermal strips were not so highly developed as those formed on intact hypocotyls. The significance of these results is discussed.