Affect Spore Germination Research Articles

Effect of Citrus Root Exudates on Germination of Chlamydospores of the Vesicular-Arbuscular Mycorrhizal Fungus, Glomus epigaeum

The effect of root exudates from Troyer citrange (Poncirus trifoliata x Citrus sinensis) on germination of surface-sterilized chlamydospores of the vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus epigaeum, was examined on water agar. Optimum temperature for spore germination was 25 C. After 7 da exposure of spores to root exudates, germination was increased from less than 10% (distilled water control) to up to 27%. Germ tube length of exudate-treated spores was more than four times greater than that of untreated spores. Root exudates stimulated branching of germ tubes, whereas germ tubes of untreated spores branched infrequently. These results indicate that root exudates affect spore germination and germ tube growth of G. epigaeum and thereby could influence subsequent root colonization and VAM formation.

Behaviour of Mycocentrospora acerina on periderm and wounded tissues of carrot roots

Development of Mycocentrospora acerina on harvested carrot roots was studied. In early storage, all prepenetration stages of the fungus were suppressed on the periderm surface; many chlamydospores remained ungerminated but viable for at least 360 days. An inhibitory principle diffused out of periderm into water or agar films. On wound surfaces, inhibition, which was inversely correlated with the depth of wound, affected spore germination only. Attempted penetration in early storage was followed by a cellular reaction resembling a hypersensitive response. Inhibitory effects were greater at 3–5° than at 15°C.

Factors affecting Spore Germination in Cowpea Isolate of Cercospora cruenta Sacc.

Factors affecting Spore Germination in Cowpea Isolate of Cercospora cruenta Sacc.

Germination of Erysiphe gratninis f.sp. hordei conidia on barley leaves

SUMMARYGermination of Erysiphe graminis f.sp. hordei conidia on leaves of several barley cultivars was studied in the laboratory. On both detached leaves and intact plants, within 48 h of inoculation a higher proportion of conidia had germinated on the basal and middle portions of the adaxial leaf surface than on the corresponding portions of the abaxial surface. Such differences between surfaces were not observed near the leaf tip. Similar results were obtained with all the cultivars and growth stages tested, and with five isolates of E. graminis, and are consistent with the observation that there is usually less powdery mildew on the abaxial than the adaxial surface of barley leaves.With most of the barley genotype/mildew isolate combinations tested, within 48 h of inoculation higher proportions of conidia germinated on seedlings and juvenile plants than on older plants. Inherited characteristics which affect spore germination on the leaf surface may be important factors in the development of adult‐plant resistance of barley to powdery mildew, particularly in certain genotypes.

DNA synthesis and nuclear division during formation of infection structures by bean rust uredospore germlings

A study was made of the requirements for DNA synthesis and nuclear division during the formation of infection structures by germinating bean rust uredospores. Actinomycin D and hydroxyurea did not affect spore germination but inhibited DNA synthesis, nuclear division, and infection structure development. Cordycepin did not greatly affect germination, DNA synthesis, formation of the appressorium, or initiation of the vesicle but did inhibit nuclear division and maturation of the vesicle. Even though the spore content of polyadenylic acid increased 1.6-fold during formation of appressoria and 6.1-fold during vesicle development, codycepin was not particularly effective in reducing either total polyadenylic acid content or synthesis in vivo. It was concluded that nuclear division need not accompany formation of appressoria or vesicles, but synthesis of DNA is required.

Pezicula malicorticis: Factors affecting spore germination and invasion of apple fruit

In aqueous suspension, conidia of Pezicula malicorticis (Jacks.) Nannf. germinated readily at the mean shade temperatures experienced in southern England in the period July to September. The percentage germination rate on cuticles detached from apple fruit, declined sharply in atmospheric humidities below 94% r.h., but conidia germinated well on intact apples stored at 93% r.h. In alternating wet and dry periods, germ-tubes were branched, with enhanced production of appressoria. Ungerminated conidia survived dry periods for up to 5 weeks, but on apples produced fewer lesions with increase in length of the period in the ungerminated state. Survival of germinated conidia depended partly on the length of the germ-tube and also on the mean ambient temperature. Extracts of apple peel containing phenolic compounds inhibited or reduced the pectolytic activity of culture filtrates of P. malicorticis . The inhibitory activity of these extracts fell as the fruit ripened both on the tree and after harvest.

GROWTH FACTORS PRODUCED BY GAMETOPHYTES OF POLYPODIUM VULGARE L. GROWN UNDER RED AND BLUE LIGHT

SUMMARYFiltrates from gametophyte cultures of Polypodium vulgare L. grown under red or blue light contain several substances affecting gametophyte development. Chromatograms prepared from red‐light‐grown cultures show two separate zones of inhibition while those from blue‐light‐grown cultures show a broad zone of promotive activity and a zone of inhibition. All the zones of activity affect spore germination, cell division and the transition to two‐dimensional growth. None affects cell length but the inhibitors cause a reduction in cell width. Most of the known effects of red and blue light on gametophyte morphogenesis can be interpreted in terms of the activity of these substances.

THE EFFECT OF AMINO ACIDS ON GROWTH AND SPORULATION OF ASPERGILLUS FLAVUS AND THEIR CARRY‐OVER FOR SUBSEQUENT SPORE GERMINATION

Summary Aspergillus flavus utilized amino nitrogen source better than nitrate, nitrite, or ammonium nitrogen sources. With casein hydrolysate as nitrogen source, optimum growth was obtained at 100 μg N/ml concentration when incubated for 8 days at 24–26° C. Using ten different amino acids singly or in mixture in Czapek's synthetic basal medium at a concentration of 100 μg N/ml, the mycelial yields were higher when the basal medium contained L‐arginine, glycine, DL‐leucine, DL‐methionine or the mixture of ten amino acids, than when casein hydrolysate was used. Abundant sporulation was obtained when the basal medium contained glycine, DL‐leucine or DL‐methionine. Spores harvested from media containing single amino acids germinated very poorly, although spores harvested from media containing casein hydrolysate, when germinated in individual amino acids, showed good germination in β‐alanine, L‐arginine, glycine, DL‐leucine, DL‐methionine and L‐tryptophane. When one of the ten amino acids was omitted from the basal medium, growth response was poor when any of L‐arginine, glycine, DL‐leucine, or DL‐methionine were absent; germination of spores harvested from media devoid of β‐alanine, glycine, DL‐leucine, DL‐methionine or L‐tryptophane was significantly poor. The combination of one or more amino acids did not show any additive effect, but each amino acid seemed to act independently. The carry‐over effects of the amino acids reflected in subsequent spore germination was conspicuous with β‐alanine, glycine, DL‐leucine, DL‐methionine and L‐tryptophane. These five amino acids when used alone or in combination with each other in the basal medium, produced spores which germinated normally; L‐tryptophane seemed to be the most important amino acid among these, as its absence in the medium markedly affected spore germination.

Fruit-spot (‘speckle’) of Jamaican bananas caused by Deightoniella torulosa (Syd.) Ellis : II. Factors affecting spore germination and infection

Some factors affecting germination of conidia of Deightoniella torulosa have been studied. In tap water on glass or on the surface of banana fruits, approximately 50% germination occurs after 1hr. incubation at 28–30 ° C. After 4–6 hr., nearly 90% of conidia have germinated. Germination does not occur below 95% R.H. : percentage germination in a water film is markedly higher than that at 100% R.H. Using a series of citrate-phosphate buffers, the optimum pH for germination and germ-tube elongation is in the range 4–6. Substances present in water extracts of banana leaves and fruit peel stimulate germination, as do drops of distilled water that have remained on the surface of young banana fruits for 24 hr. Solutions of several compounds present in synthetic nutrient media provide better germination than does distilled water; some carbohydrates tested are particularly favourable. The longevity of D. torulosa conidia is dependent on external humidity. Viability is lost within 3–4 days at R.H. < 95%. At 98% R.H. , a small number of conidia may be viable after 10 days storage. The severity of fruit-spot caused by D. torulosa increases progressively with advancing maturity of fruit. Spotting tends to be most intense near the tips and on the inner sides of individual fingers. Presence of dew or rain water appears to be essential for successful infection by D. torulosa . Experimental inoculations have shown that resistance to infection increases to some extent as the fruit matures. The severity of fruit-spot undergoes seasonal variation, being highest after the rainy periods during April–May and September–October. D. torulosa sporulates on diseased, dead or dying leaves, withering flower parts and on transition leaves and bracts. The relative importance of these inoculum sources in relation to fruit-spot epidemiology is discussed. Removal of dead or dying ‘trash’ leaves from the plantation at frequent intervals is recommended. Isolates of D. torulosa from fruit-spots are able to cause a spotting of banana leaves (‘black-spot’) and a rotting of the tips of banana fruits (‘black-tip’). Conversely, isolates from ‘black-spot’ and ‘black-tip’ lesions may cause fruit-spot. A black scab-like fruit-spot, also caused by D. torulosa , occurs in a few widely separated plantations.

Some effects of pea root exudates on physiologic races of Fusarium Oxysporum Fr. F. pisi (Linf.) Snyder & Hansen

Exudates from the roots of the pea cultivars, Onward, Alaska and Delwiche Commando, which differentiate between three physiologic races of Fusarium oxysporum f. pisi , affected spore germination in the three races differentially, depressing the germination of races they resisted more than of those to which they were susceptible. Exudates from young seedlings depressed germination more than did those from roots of older plants, and the activity of exudates increased temporarily when side roots were first formed. When concentrated root exudates were contained in porcelain cylinders on agar sown with spores, zones of differential growth formed around the cylinders; when the exudate was from a cultivar resistant to the race whose spores were plated, the zone was one of growth inhibition, and when from a susceptible cultivar, it was one of growth stimulation. Notwithstanding this effect on spore germination, exudates from the different cultivars had no differential effect on the rate at which germ tubes or mycelium of the individual races grew. Sections through roots of cultivars inoculated with a race they resist showed that the mycelium invaded only the outer cortex. Plants susceptible to F. oxysporum wilt less when simultaneously infected with F. solani ; xtracts of the bases of pea plants infected with F. solani inhibited the germination of spores of F. oxysporum , whereas extracts from normal stem bases did not.