Fungal Infection Process Research Articles

Phenylalanine ammonia-lyase in barley: activity enhancement in response to Erysiphe graminis f.sp. hordei (race 1) a pathogen, and Erysiphe pisi, a nonpathogen

Phenylalanine ammonia-lyase (PAL) activity in barley leaves was measured at intervals after inoculation with the powdery mildew pathogen Erysiphe graminis f.sp. hordei. Measurements were made at times that included the periods of attempted penetration by the E. graminis primary germ tube and appressorium. The results demonstrated that extractable enzyme activity increased at 6 h and between 12-15 h after inoculation, times consistent with attempted penetration by the primary germ tube and the appressorium, respectively. Enzyme activity increased regardless of the resistance or susceptibility of the barley cultivar to the fungus suggesting that the response was non-specific and was not a reflection of the resistance or susceptibility of the cultivar to the pathogen prior to the time of penetration. When barley was inoculated with the nonpathogen E. pisi, only a single period of elevation in PAL enzyme activity was detected. This was consistent with the fact that, unlike E. graminis, E. pisi does not produce a primary germ tube. The enzyme activity increased between 9-15 h after inoculation, consistent with the time of the attempted penetration of the leaf by the E. pisi appressorium. Northern blot analyses to detect the time of appearance of PAL mRNA indicated that the level of the message began to increase at 0·5 h after inoculation with both fungi, and that the intensity of the increase was greatest in response to E. pisi. The results are discussed with respect to the presumed importance of host phenolic compound metabolism that occurs as a response to the fungal infection process.

Adhesion Pad Formation and the Involvement of Cutinase and Esterases in the Attachment of Uredospores to the Host Cuticle.

We have investigated the basis of adhesion of uredospores of the obligately parasitic rust fungus Uromyces viciae-fabae to leaves of its broad bean host. Upon contact with an aqueous environment, spores form a structure that we have termed an adhesion pad. The adhesion pad is formed by both living and autoclaved spores, but only adhesion pads formed by living spores adhered to the cuticle of leaves of the host plant. Treatment of living spores with the serine-esterase inhibitor diisopropyl fluorophosphate prevented the adhesion of the pad to the leaf surface, suggesting a functional role for esterase or cutinase in the process of adhesion. A cutinase and two nonspecific serine-esterases were found to be localized on the surface of spores. These enzymes were released rapidly from the spore surface upon contact with an aqueous environment. The addition of the cutinase and the nonspecific esterases to autoclaved spores restored their ability to adhere to the host cuticle. Thus, whereas pad formation appears to be a passive response to the aqueous environment, the actual adhesion of pads to the host cuticle appears to depend on the cutinase and esterases associated with the spore surface. These results suggest a new role for cutinases and serine-esterases in the fungal infection process.

Facial Granuloma Associated With Trichosporon cutaneum Infection

A 23-year-old woman presented with Trichosporon cutaneum, which invaded deep into the dermis and subcutaneous tissue of the face and developed chronic granulomatous reactions. We postulated that the local use of an occlusive dressing with topical corticosteroid ointment in the early stage of the infection played a role in promoting the process of this opportunistic fungal infection. Antifungal chemotherapies, selected according to sensitivity testing to the isolated organism, were unsuccessful, mainly because of the acquired resistance of the organism to the chemical agent. Surgery was finally performed and a good result was obtained.

Status of the Aflatoxin Problem in Corn

AbstractAflatoxin, a potent carcinogenic metabolite produced by the fungus Aspergillus flavus, has been clearly demonstrated to be a kernel contaminant in both preharvest and postharvest corn. Research has been conducted on: (i) fungus invasion of the ear; (ii) effects of the environment on aflatoxin levels; and (iii) methods of control.A. flavus infects developing ears in both southern and corn belt regions but growing conditions in the southern U.S. are more conducive to the fungal infection process and subsequent toxin production. Most observations indicated that a break in the pericarp is necessary for fungal establishment. Insects, particularly larvae of the second European corn borer, corn earworm, and fall armyworm, have been implicated in causing breaks as well as serving as vehicles for carrying the inoculum to the potential infection site. Conditions of stress such as those caused by drought have been shown to enhance the aflatoxin contamination problem. Suggested control methods are: (i) plant only adapted hybrids with the highest level of resistance against ear‐damaging insects; (ii) employ management practices that will either reduce stress or shift the ear development stage to miss a likely stress period.Preliminary results suggest that either A. flavus growth or aflatoxin levels are under genetic control, but corn genotypes cannot be recommended at this time that would entirely eliminate the aflatoxin contamination problem in corn.

Effect of isoprothiolane on the infection process of Pyricularia oryzae.

Isoprothiolane (IPT), diisopropyl 1, 3-dithiolane-2-ylidenemalonate was tested for its effect on vegetative growth and infection process of Pyricularia oryzae Cav. Mycelial growth in a glucose-yeast extract liquid medium was inhibited completely at 20ppm, and partially at 10 and 5ppm. Abnormal hyphae like chlamydospore cells were frequently formed in the presence of IPT. IPT at 2ppm did not affect conidial germination and appressorium formation, but almost completely inhibited penetration when treated at the pre-germination stage. Treatment of the fungus with IPT at different stages of the fungal infection process revealed that IPT inhibits penetration and growth of infection hyphae rather than conidial germination and appressorium formation.