Volume 75, Issue 3
March 1972, pages 105-154
pp 105-110 March 1972
The effect of L-tyrosine, DL-phenylalanine, shikimic acid and chlorogenic acid on sporulation was studied with six isolates ofPyricularia from different gramineous hosts. In general, the isolates from cultivated Gramineae sporulated better than the isolates from the wild grasses. The effect of the compounds on sporulation varied with the isolate. Possible genetic differences among the isolates are invoked to explain the results.
pp 111-116 March 1972
Discosiella cylindrospora H. and P. Sydow, the type species of the genusDiscosiella H. and P. Sydow, is redescribed from a study of type material. It is concluded that the conidial appendages of this fungus are mucoid in nature, a fact not mentioned by the Sydows in their diagnosis and description. The diagnosis ofDiscosiella is suitably emended. From the original description ofD. longiciliata Agnihothrudu, supplemented by a study of the type material of this species, it is concluded that it cannot be retained in the genusDiscosiella as emended in this paper and is now accommodated in a new genusDiscosiellina asD. longiciliata (Agnihothrudu) comb. nov.
pp 117-128 March 1972
An earlier report of chromosome numbers of 2n=22 andn=11 is confirmed forGliricidia sepium (Jacq.) Steud. A supernumerary isofragment chromosome (SIF) in 32·41% of the nuclei at diakinesis and 30·00% of the PMCs at metaphase I is reported in the genus for the first time. The occurrence of the SIF was not consistant even in the PMCs of the same anther. Often the SIF exhibited inter-arm (fold back) pairing and behaved irregularly during meiosis probably due to a very weak centromeric activity. There seems to be a certain affinity between the SIF and one of the two nucleolar bivalents. It is hypothesized that the SIF could have arisen as a result of a disarticulation at the secondary constriction of a chromosome of one of the two nucleolar bivalents. The SIF has originated probably during one of the pre-meiotic mitoses in the sporogenous tissue since it was absent in some PMCs of an anther and in the somatic cells (of root tips and leaf tips). The SIF was mostly subjected to meiotic elimination through the formation of micronuclei (15·2%). In the other PMCs it is probably included in the microspore nuclei. The presence of the SIF or a deficient nucleolar chromosome in the pollen grains is considered to be responsible for about 8·15% of pollen sterility in excess to the normal. Neither uniform nor significant effects of the SIF have been noticed on meiosis nor does it produce any discernible morphological effects.
pp 129-139 March 1972
Christisonia subacaulis, a member of the Orobanchaceae, is a total leafless root parasite onThemeda cymbaria.
The anther is bisporangiate and monothecous. The microsporangial wall includes epidermis, one or two middle layers and endothecium. The pollen grains are 2-celled, tricolpate and spheriodal.
The ovary is bicarpellary syncarpous, unilocular with many unitegmic tenuinucellate ovules attached on the four placentae. The placentation is parietal.
The hypodermal archesporial cell directly functions as megaspore mother cell, It undergoes meiotic divisions resulting in a linear tetrad of megaspores. The chalazal megaspore functions and the micropylar megaspores degenerate. After three free nucellar divisions in the functional megaspore, a 8-nucleate embryo sac is formed. The mature female gametophyte consists of an egg apparatus with two synergids and an egg. The antipodal cells are large and persistent. The secondary nucleus lies near the egg.
The endosperm isab initio cellular. The micropylar haustorium is 2-celled and uninucleate while chalazal haustorium is unicellular and uninucleate.
pp 140-144 March 1972
Sporulation ofPyricularia isolates were generally depressed by most of the phenolic compounds under the experimental conditions. However, many of the compounds tended to induce conidial formation in the otherwise non-sporulating isolate fromB. mutica. Caffeic acid and guaiacol for the isolate fromO. sativa, coumarin for the isolate fromE. coracana and cinnamic acid for the isolate fromP. repens were stimulatory for sporulation. As judged by their growth response, the isolates fromO. sativa andB. mutica tolerated a wider variety of phenols than the isolates fromL. hexandra andP. repens. The isolates fromE. coracana andS. italica showed an intermediate response.
pp 145-154 March 1972
Except for the isolate fromS. italica, all other isolates ofPyricularia sporulated best on detached injured leaves ofT. vulgare andS. italica as compared to their natural host leaves in light. The observed results are ascribed to heterokaryosis and production/selection of sporulating biotypes rather than to the stimulation of sporulationper se of the isolates by special pre- or post-inoculation compounds in the detached leaves.