1970 Volume 36 Issue 4 Pages 250-253
Observation on the process of infection of red clover by Kabatiella caulivora was made to compare the response of resistant and susceptible clones of host plant.
Conidial germination by germ tube formation on the epidermal tissues began 16 hours after inoculation, and actual penetration was observed 48-72 hours after inoculation. Appressoria were not detected.
There was no difference in percentages of conidial germination on the epidermal tissues between resistant and susceptible clones. Hyphae were found to penetrate through cuticular layer. In the case of the resistant clones, cells at the infection site were not killed in the early stage of infection.
Growth of the fungus within the host tissue was as follows: hyphae 2.5-4.0μ in diameter elongated in the intercellular space and reached phloem but no haustorium was observed within the cells. The hyphae did not penetrate into the xylem, but into the phloem. In the phloem, hyphae increased from 2.5-4.0μ to 8.0-12.5μ in diameter and formed abundant branches and septa. Finally the phloem collapsed.
The difference in the hyphal growth and symptom development between the tissue of both clones was as follows. Symptoms: elongated lesions about 20mm in length, having water-soaked appearence, appeared on the petioles of the susceptible clone 6 days after inoculation; conversely, there were minute black flecks on those of the resistant clone 7 days after inoculation. Sometimes lesions with black margin appeared on the petiolules of the resistant clone 9 days after inoculation. Hyphal growth: microscopical observation was made on transverse sections of young lesions 7 days after inoculation. Degenerated cells, showing a slight browning, extended to the phloem in the susceptible clone. These degenerated cells finally collapsed. Conversely in the resistant clone, degeneration of the infected tissue showing deep browning was limited to 2-3 cell layers. These cells were found to be coagulated.
Regardless of the water-soaked type or the minute black fleck type of lesions, hyphae were observed in the intercellular space of tissues around the lesions.