Volume 68, Issue 3
September 1968, pages 111-168
pp 111-130 September 1968
Detailed study was made of the effect of (i) various inorganic and organic sources (potassium nitrate, ammonium sulphate, ammonium nitrate, asparagine, urea) and (ii) various levels of nitrogen (280, 700, 1,400 and 2,100 mg. N per litre) on growth and metabolism ofD. sorokiniana. Observations on mat weight, spore numbers, shift in pH of the medium, nitrogen accumulated in the mat, residual nitrogen (total, nitrate and ammoniacal nitrogen) and residual sugar in the medium were made after incubation for varying periods. The results are presented in detail and discussed.
pp 131-142 September 1968
Five chemical mutagens, namely, pyrogallol, pyrocatechol, quinol, acenaphthene and coumarin were employed to induce mutations in sugarcane. Settlings and setts of Co. 419 were treated with these chemical agents. Three different methods were adopted to administer the mutagens. The L.D.50 value for pyrogallol and pyrocatechol seemed to differ a hundred-fold when buds were treated, whereas they appeared to be the same when the settlings were subjected to treatments. The optimum strength for induction of mutations and tissue damage appeared to be between 0·01 M and 0·001 M for pyrogallol, pyrocatechol and quinol. Mutations for shortened internodes and glabrous leaf-sheath were induced by pyrogallol and pyrocatechol. Tissue damage such as partially dissected lamina occurred when treatments with pyrogallol, pyrocatechol and acenaphthene were applied. Pyrocatechol and acenaphthene induced profuse tillering whereas quinol and coumarin suppressed tiller formation. The vast scope for chemical mutagenesis in sugarcane is indicated.
pp 143-149 September 1968
pp 150-162 September 1968
It had been shown previously that the resistance of sugarcane variety Co. 453 to root rot caused byPythium graminicolum, is associated with the presence in its rhizosphere of a high proportion of bacteria and actinomycetes capable of inhibiting the growth ofP. graminicolum, in vitro, as also of antagonistic fungi likeTrichoderma viride andPenicillium rugulosum which inhabit the rhizosphere of this variety by virtue of their ability to parasitise mycelia of certain Mucorales. Conversely, this type of microflora is absent from the rhizosphere of the susceptible variety, Co. 419.
Root interaction is known to profoundly affect the growth of plants. A study was undertaken to see if root proximity of the root rot resistant and susceptible varieties, Co. 453 and Co. 419 respectively, would affect their reaction to the disease and if so, whether the latter would be correlated with the effects on the rhizosphere microflora of the two varieties. In mixed cultivation, Co. 419 acquired a degree of resistance, but Co. 453 did not lose its resistance. There was a quantitative increase in the numbers of bacteria, actinomycetes and fungi in the rhizosphere of each of the components of the mixture as compared with uniculture in each of two soils used in the study. The proportion of antagonistic actinomycetes in the rhizosphere of Co. 453 increased, while the proportion in that of Co. 419 remained about equal to that in uniculture. Although the numbers of bacteria increased, there was little change in the proportion of antagonistic members.
In mixed culture, there were striking changes in the species of fungi occurring in the rhizosphere of each of the two varieties. Certain Mucorales likeRhizopus stolonifer andCunninghamella bertholettiae and the antagonistic fungi,Trichoderma viride andPenicillium rugulosum characteristic of the rhizosphere of Co. 453 in uniculture were found to occur in that of Co. 419 while others characteristic of Co. 419 likeFusarium moniliforme andDrechslera oryzae moved into the rhizosphere of Co. 453.
In the absence of bacteria and actinomycetes, interchange of fungal species between the rhizospheres of the varieties occurred as in their presence. No interchange of antagonistic bacteria and actinomycetes was apparent in the presence or absence of fungi, but intensification of the rhizosphere effect on bacteria and actinomycetes occurred irrespective of the presence or absence of fungi.
It was shown that Co. 419 became resistant toPythium root rot under the influence of mixed culture with Co. 453, only in the presence of the fungal component of the rhizosphere and not in the presence of the bacteria and actinomycetes alone in the absence of fungi. On the other hand, it was seen that Co. 453 owed its resistance to the fungi as well as to the bacteria and actinomycetes.
pp 163-168 September 1968
The two isolates ofFusarium solani f.aurantifoliae responsible for lime twig disease were found to utilise carbon from a wide variety of compounds. In general, monosaccharides proved to be better than other sources tested for growth and sporulation though maltose exhibited best growth.
In both the isolates mannose supported best growth among hexoses. Pentoses were less readily utilized than the hexoses. Among disaccharides, maltose proved to be the best carbon source out of all the 14 different compounds tested. As compared to dextrin, starch proved to be the better source. Alcohols did not prove to be satisfactory sources for both the isolates.