Studies on the Release, Survival And Germination Of Conidia Of Phyllactinia Corylea (Pers.) Karst.

Abstract

Conidia of P.corylea germinated best at 25 - 28˚c. and germinated well, uniformly and at the same rate at any humidity from zero to 100% R.H., but poorly in liquid water. Germ tubes conidia germinating at lower humidities were short whilst those at high humidities were fairly long. Approximately 30 per cent of both germinated and ungerminated conidia shrivelled when incubated. at 0% R.H. This value decreased with rise in humidity to show shrinkage in only one per cent of conidia held at 100% R.H.

The conidia had a brief latent period of germination of 2 - 3 hours. The germinating conidia usually produced a single germ tube and occasionally two. Branching of germ tubes was rare on glass surface but appressoria were freely formed. On the host (Carica papaya) leaf surface the germ tubes grew randomly over the epidermis am equally freely formed appressoria. The appressoria were either terminal, intercalary or lateral. Germ tubes produced at lower humidities collapsed and shrivelled within a few hours after emergence. All germ tubes produced and held at 0% R.H. shrivelled in 11 hours and those at 80.3% R.H. in 30 hours. Those at 92, 96.9 and 100% R.H. showed 94.5, 25.0 and 20.2% of shrivelled germ tubes respectively in 48 hours.

The Conidia germinated better in light and produced longer germ tubes but formed fewer appressoria than those incubated in darkness.

Conidia stored at 5˚c and at various relative humidities were preserved longest at the higher humidities and died quickest at the lower humidities. Longevity was however brief and did not exceed 20 days at any humidity. Multicellular, non-branching conidiophores, commonly 300 u long, arose perpendicularly from the superficial mycelium. Each was terminated by a generative cell which formed the conidia. Usually only one mature conidium was distinguishable at the tip of the conidiophore. Immediately after maturation of the conidium the generative cell bent approximately at the middle while the two arms of the cell stood at right angles. This movement loosened the attachment of the conidium to the conidiophore and the conidium fell at the slightest disturbance. The bent generative cell then abstricted the next conidia. In still air conidial chains were readily formed. A few conidia germinated whilst still attached to the conidiophore. The conidia matured predominantly in the dark and heaviest crop of spores were obtained in the morning.

The rate of bending of the generative cell was the same at 20 and 28˚c., in light and in dark and at 76 and 100% R.H. The ourvature in the generative cell remained unaltered in sucrose solutions and in water. The generative cell was not phototropic Whilst the entire conidiophore