Plant Pathology Commons^™

Studies On The Biology Of Striga Aspera (Scrophulariaceae) In Nigeria, Emmanuel Izaka Aigbokhan

Biological Sciences Theses & Dissertations

Studies on Striga aspera are few and little information exists on its relationship with the morphologically similar and much studied S. hermonthica. Both species are sympatric in West Africa and if they hybridize, may serve as virulent gene reservoirs for each other.

The primary focus of this study was on the biology of S. aspera in Nigeria. The research focussed on its distribution, phenology, cytology, hybridization, seed dormancy, viability and germination in relation to S. hermonthica. Related studies involving the hybrids include genetic and morphological variability, pathogenicity and the simultaneous dual infection of a maize plant by both species.

In …

Biosystematics And Diversification In The Genus Striga Lour. (Scrophulariaceae) In Africa, Kamal-Eldin Ibrahim Mohamed

Biological Sciences Theses & Dissertations

Of the 34 taxa of Striga (29 species) that occur in Africa, 25 are endemic. Species diversity differs from region to region. The subtropical zone has 74% of the taxa including 41% endemics. Within this region, the West African part (from Senegal to eastern Nigeria) has 62% of the total taxa including 24% endemics. South of the equator the number of taxa is 56% of the total with 21% endemics, a proportion slightly less than that for West Africa. I recognize 29 species based on extensive herbarium and field studies. A new species from Angola is described. Striga yemenica previously …

Studies On The Giant Mealie Witchweed, Striga Forbesii Benth., In Zimbabwe, David Allen Knepper

Biological Sciences Theses & Dissertations

Of the seven species of Striga found in Zimbabwe, S. forbesii Benth. is currently the most destructive in terms of crop damage. Owing to its limited occurrence worldwide as a pest of crops, relatively little work has been done on this species.

Striga forbesii has been found to be a consistent problem on both maize and sorghum in the Hunter's Road District of KweKwe, Zimbabwe. Results of a pot study and field observations, indicate S. forbesii can successfully parasitize Urochloa panicoides Beauv., Sorghum arundinaceum (Desv.) Stapf, and Rottboellia cochinchinensis (L.) L.f., all of which are widespread weeds of arable land. …

The Pollen Exostructure Of Striga (Scrophulariaceae), Mark A. Deleonardis

Biological Sciences Theses & Dissertations

In this survey, the pollen exostructure of 13 Striga species was examined using light microscopy and scanning electron microscopy. Two of the 13 species were also observed by transmission electron microscopy to assess major differences in exine composition. Striga pollen is consistently spherical to oblate, isopolar, tectate, and three or four colpate. Sculpturing may be psilate, psilate-perforate, finely rugulate, or coarsely rugulate. The equatorial width of the species surveyed ranged from 15 to 30 micrometers. It is concluded that variation in Striga pollen sculpturing, aperture structure, and size support the current taxonomy of the genus.

Germination And Host Range Of Branched Broomrape (Orobanche Ramosa) From Texas, Robert D. Coffin

Biological Sciences Theses & Dissertations

The effect of temperature on the germination of Orobanche ramosa L., branched broomrape, was investigated by dividing the physiological stages leading to germination into discrete events: pretreatment, a period when the seed becomes receptive to stimulant, and posttreatment, when stimulant application (GR-24) induces germination. Seed was pretreated and posttreated at 16 different temperature combinations. Optimal pretreatment was at 15°C and 18°C, maximum posttreatment at 18°C. Highest germination was obtained by pretreating and posttreating seed at 18°C, lowest at 24°C. The effect of different pretreatment regimes was tested. Seeds were pretreated over moist filter paper and in soil for Oto …

Germination And Haustorial Development In Orobanche Minor Smith (Orobanchaceae), David L. Spelce

Biological Sciences Theses & Dissertations

Orobanche minor Smith is an introduced root parasite that is known to attack some commercial crops. Germination occurs only after a preconditioning period involving moisture which must be followed by a chemical stimulant produced by the host root. Strigol and strigol analogs (GR-compounds} have been reported to germinate some species of Orobanche. Statistical tests indicate a significant difference between the effectiveness of strigol, GR-7 and GR-45 (P = 0.001).

The embryo is an undifferentiated mass of cells. During germination, the radicular pole of the embryo differentiates into the radicle, while the plumular pole remains undifferentiated. The radicle forms the primary …