Sporangial Suspension Research Articles

Effect of ridge gourd pollen on zoospore germination ofPseudoperonospora cubensis and its significance in epidemiology

Ridge gourd pollen has a stimulatory effect on the germination ofPseudoperonospora cubensis. The rate and percentage germination of zoospores increased in the presence of pollen leachates. Spraying of leaves with a mixture of pollen and sporangial suspension enhanced the development of lesions. Early germination of zoospores in the presence of pollen proved advantageous for infection as it provided a prolonged favourable infection period. The results are discussed in relation to the epiphytoties of the disease during flowering period.

Screening of Carica papaya L. Seedlings for Resistance to Root Rot Caused by Phytophthora palmivora Butl.1

Abstract Papaya seedlings being tested for resistance to Phytophthora palmivora root rot were inoculated with sporangial suspensions which varied from 0 to 18,000/plant. Mortality counts and disease ratings of seedlings taken 1 month after inoculation showed that: (a) developmental resistance increased as seedlings became older and appeared totally developed by the time seedlings were 2 months old; (b) comparisons among papaya lines inoculated with increasing concentrations of inoculum demonstrated a dosage response; (c) 1-month-old papaya lines inoculated with a uniform concentration of inoculum (5,250 sporangia/plant) could be separated into 3 distinct groups. Line 8, ‘Waimanalo’-23, ‘WaimanaIo’-24, and line 40 were resistant; 45-T22 and ‘Kapoho Solo’ were moderately resistant and ‘Higgins’ was susceptible. The correlation between greenhouse and field mortality was r = 0.955, which supports the reliability of the method.

Resistance to False Rust in Winged Beans1

Abstract An inoculation technique was developed to test seedling plants of winged beans (Psophocarpus tetragonolobus (L.) DC.) for resistance to false rust disease incited by the fungus Synchytrium psophocaropi (Rac.) Gaumann. Sporangia were collected in distilled water by washing or scraping from infected, sporulating winged bean leaves. Inoculum was applied by brushing the sporangial suspension onto the 1st or 2nd true leaves of seedling plants, and holding the inoculated plants under high humidity conditions for 24 hours. Intensity of infection can be scored 10 days after inoculation. Resistance appears to result from a hypersensitive reaction.

Effects of light during infection on the incidence of downy mildew ( Pseudoperonospora cubensis) on cucumbers

Pseudoperonospora cubensis, the causal agent of downy mildew of cucurbits, infected cucumbers under either dark or light conditions. Infection at 20 °C was markedly enhanced when a short wet period was associated with illumination of relatively low photon flux density. The optimal temperature for infection in darkness at 2 and 4 h of wet period was 25 and 15 °C, respectively, whereas in light it remained constantly at 20 °C. About 90% of the zoospores of the pathogen settled on stomata of illuminated cucumber leaves within 2 h from inoculation with freshly-prepared sporangial suspension compared to about 75% that did so within 3 h in darkness. Fungal penetration occurred through stomatal openings. Darkness and DCMU did not prevent zoospore settlement on stomata, hence, high disease levels were obtained on DCMU-treated plants inoculated in darkness. When wetness was applied for a short period of 2·5 h, plants exhibited some diurnal periodicity in proneness to infection which was highest at midday. The results explain the high incidence of downy mildew in dry seasons in semi-arid growing areas where dew is the major source of free leaf moisture.

Fluorescence microscopy and related enzyme activity of sunflower plants infected by Plasmopara halstedii

Fresh sections of healthy and infected sunflower tissues were examined with the aid of a Jena Universal fluorescence microscope, equipped with exciters BG 12 2 and UG 1 1·5 , and a barrier filter GG9. Two weeks after bud-inoculation a blue-yellowish fluorescence was observed in parenchyma cell walls of stems, petioles and leaf main veins taken from infected plants. Fluorescence was more intense in cell wall corners adjacent to intercellular spaces. No such fluorescence was detected in healthy corresponding tissues. As pathogenesis progressed, fluorescence of cell walls intensified and some cells became full of fluorescing material. Peroxidase activity increased 4-fold in leaves and 13-fold in stems as a result of infection. β-Glucosidase activity was remarkably high in sporangial suspensions and in invaded leaves, but not in fungal-free tissues of infected plants nor in healthy ones. It seems likely that scopoletin was the major fluorescing compound accumulated. A causal link is suggested between the increase of fluorescence and the enhancement of β-glucosidase and peroxidase in infected sunflowers.

Phenylalanine ammonia lyase, chlorogenic acid and lignin in potato tuber tissue inoculated with Phytophthora infestans

Tuber disks of Majestic (susceptible-r) and Orion (resistant-R 1) were inoculated with a sporangial suspension of Phytophthora infestans race 4. There were increases in the activity of phenylalanine ammonia-lyase and the level of chlorogenic acid, accompanied by the accumulation of a lignin-like polymer. All three changes were faster in Orion than in Majestic. Lignification was relatively slow and diffuse in the widespread infected area of slices from Majestic but more rapid in the centre of the restricted infected area of Orion slices. Phenylalanine ammonia-lyase activity followed a similar pattern. It seems probable that lignification is involved in the restriction of the spread of the pathogen in Orion slices, and that it is controlled in part by the level of phenylalanine ammonia-lyase.

Susceptibility of potato tubers to infection by Phytophthora infestans

SUMMARY Phytophthora infestans infects King Edward potato tubers more readily through inoculated eyes than through lenticels, but more lenticels than eyes became infected when whole tubers were sprayed with inoculum. The resistance of lenticels but not of eyes increased as tubers aged. The spores did not infect through intact periderm. The likelihood of tubers on plants grown in pots becoming infected by sporangial suspension poured on to the soil increased the nearer the tubers were to the soil surface, the stem, or the side of the pot. Naturally infected tubers, and those sprayed with sporangial suspension, had most eyes infected at the rose end, and most lenticels infected on the middle region of the tuber. Of naturally infected tubers, on which the site of infection could be identified, most were infected through eyes at the rose end.