Indirect Germination Research Articles

An account of some physiological studies in two species of phytophthora

The paper deals with some physiological studies of two typical strains ofPhytophthora palmivoraButl. andP. parasiticaDast. var.macrosporaAshby causing severe fruit rots ofAchras sapota L. andAnona squamosa L. respectively. The effect of temperature on the germination of sporangia had a marked effect. Maximum percentage of indirect germination (by formation of zoospores) occurred at 20° C, whereas direct germination of sporangia (by formation of germ tube) was at 30° C, which further continued upto 37° C. Maximum indirect germination at 20° C shows the favourable cool temperature for the epidemic of the diseases (Fruit rots) in nature. The best substrate (medium) for germination of sporangia was found to be tap water. Next to this was the host decoction or extract. Glucose solution also accelerated sporangial germination. The effect of two dyes viz., Malachite green and crystal violet was also studied in relation to growth and sporulation ofPhytophthora isolates. Their addition to the medium in various fractional dilutions had a profound influence in the rate of growth and sporulation. An interesting observation noted was that growth of the isolates was inversely porportional to the various concentrations of the dyes, under study. An attempt was also made to study the influence of various vitamins. In all, six vitamins were included in the study. Out of these, thiamine and riboflavin were found to be the best sources promoting good growth and sporulation of both the species ofPhytophthora under study.

Asexual reproduction in Phytophthora erythroseptica

Sporangia are readily produced by Phytophthora erythroseptica Pethybr. when mycelial mats are grown in pea broth, washed and transferred to shallow layers of water or Petri's solution. Sporulation occurs between 8 and 26 ° C., (opt. c . 18–22 ° C.). Aeration of water is not necessary for sporangial production. Light stimulates more abundant sporulation but prolonged exposure to light is unnecessary. Sporangia are produced within a pH range of 4·0–8·5 (opt. c . pH 7·0–7·5). In colonies grown entirely in a synthetic liquid medium the addition of various carbon sources or thiamin did not induce normal development of sporangia. Direct germination was stimulated by fairly high temperatures while indirect germination was induced by cooling the cultures for a short period followed by a return to normal room temperatures. Sporangia in cultures frequently burst discharging undifferentiated protoplasm. A high percentage of bursting occurs in young cultures, especially when they are exposed for relatively long periods to low temperatures. Possible relationships between the fine structure of sporangia and the germination processes are discussed.

The fine structure of sporangia of Phytophthora erythroseptica Pethyb.

SUMMARY Young non-germinating sporangia of Phytophthora erythroseptica contain nuclei and cytoplasmic organelles, similar in appearance to those in other fungi, and a conspicuous central and other vacuoles. The sporangial wall consists of an outer homogeneous layer and an inner vesicular layer, prominent in the apical region. Peripheral cytoplasmic vacuoles are frequent, particularly where the vesicular layer is well developed. In old sporangia, which lose the ability to germinate indirectly (i.e. to produce zoospores), there is no vesicular layer and there is a change in the nature of the storage material of the vacuoles. When young sporangia are stimulated to indirect germination by low-temperature treatment the central storage vacuole disappears and there is a marked elongation of mitochondrial cristae, consistent with an increased rate of respiration. The sporangial wall becomes three-layered with the development of an inner homogeneous layer which separates the plasma membrane from an increasingly prominent vesicular layer. In the region of the papilla the vesicular layer shows a striking increase in thickness; it is suggested that this layer and the inner homogeneous layer play an important part in zoospore discharge.

The nuclear phenomenon of Phytophthora capsici Leonian in connection with the two types of sporangial germination

Nuclear phenomenon of the fungus, Phytophthora capsici Leonian, has been examined at the sporangial stage in two types of germination. Nuclei in sporangia, in germ-tubes, and in zoospores stained well with a modified HCl-Giemsa technique. Distinct differences with regard to the appearance of nuclei (DNA) in the germinating stage were observed. There are two groups of sporangia which differ in form and number of the nuclei. In one group, the nuclei are globate and large, varying between 3 and 28 in number. In the other group, the nuclei are more elongate and small, varying from 23 to 49 or more in number. In the former group, there is a high correlation between the number of globated and large-sized nuclei and the length of sporangia, but it is not so in the latter group.Number of zoospores in the former group sporangium ranges from 8 to 28. When zoospores are released from sporangium, they are still uninucleate. These may result in indirect germination. In the other group of sporangia, however, zoospores retain polynuclear condition for a long time, and this seems to cause direct germination. The occurrence of these large and small nuclear types is in a proportion of 83.9:16.2.These facts are in accord with the data given by numerous studies relating an appearance of the two types of sporangial germination. The two types of sporangial germination proved the inherent nature of their occurrence having for their rates 83.9 and 16.1 for indirect and direct germination of sporangium, respectively.