Evaluation of wild perennial Glycine species for resistance to soybean cyst nematode and soybean rust

The genetic base for soybean cultivars is narrow compared to most other crop species. Twenty-seven wild perennial Glycine species comprise the tertiary gene pool to soybean that may contain many genes of economic importance for soybean improvement. We evaluated 16 accessions of G. argyrea, G. clandestina, G. dolichocarpa, and G. tomentella for resistance to Heterodera glycines (HG), also known as the soybean cyst nematode, and to multiple isolates of Phakopsora pachyrhizi, the causal fungus of soybean rust. All 16 accessions were classified as resistant to H. glycines HG Type 2.5.7, based on number of cysts per root mass with plant introductions (PIs) 483227, 509501, 563892, and 573064 (all G. tomentella) void of any cysts indicating no reproduction by this pest. All 16 accessions had an immune reaction to one isolate of P. pachyrhizi. Regardless of isolate, no sporulating uredinia were observed on G. argyrea (PI 505151) and G. tomentella (PIs 483227, 509501, and 573064). These results demonstrate that some accessions within the perennial Glycine species harbour resistance to both H. glycines and P. pachyrhizi and would be good candidates for wide hybridization programs seeking to transfer potentially unique multiple resistance genes into soybean.     

Influence of Congeneric Aquaculture on Hard Clam (Mercenaria spp.) Population Genetic Structure

Throughout their range, hard clams of the genus Mercenaria support important commercial fisheries, and hard clam aquaculture is rapidly developing in several regions, including Florida, USA. Commercial hard clam aquaculture in Florida waters originated in the Indian River Lagoon during the late 1970s, but by the early 1990s the focus of the industry had shifted to Cedar Key on the west coast of the state. There, the species Mercenaria campechiensis predominates the natural hard clam population, whereas Mercenaria mercenaria is predominant in the local aquaculture industry. The two species hybridize extensively. The present study was conducted to estimate the genetic implications of M. mercenaria aquaculture on the natural population of M. campechiensis that occupies Cedar Key waters. We sampled a variety of marine and estuarine habitats surrounding Cedar Key and collected 257 hard clams for analysis of species-specific diagnostic allozyme loci, age, and the presence and stage of gonadal neoplasia. Results indicate that the composition of the hard clam population has changed since the advent of aquaculture (i.e., post-aquaculture). Members of the species M. mercenaria were practically nonexistent prior to the 1993 initiation of aquaculture in the area but increased significantly in abundance post-aquaculture, as did hybrid hard clams. There was no significant difference in the abundance of M. campechiensis pre- versus post-aquaculture. All genotype classes had a high incidence (>80%) of gonadal neoplasia, although it is not clear if this high incidence is a reflection of the introduction of aquaculture into the area or if neoplasia was a common feature of the population prior to 1993. Regardless, this finding is not consistent with previous reports that neoplasia is more common in hybrid hard clams. Overall, the results of this study provide clear evidence that culture of M. mercenaria can influence the genotype composition of naturally occurring congeneric populations in the vicinity of the culture operation. The long-term implications of that influence remain to be seen.     

Depletion of isoeugenol residues from the fillet tissue of AQUI-S™ exposed rainbow trout (Oncorhynchus mykiss)

There is a critical need in U.S. public aquaculture and fishery management for an approved sedative that allows for the immediate release of fish after sedation. AQUI-S^TM is a fish anesthetic/sedative approved for use in several countries and until recently was being developed in the U.S. as a sedative for immediate release of fish after sedation. The U.S. National Toxicology Program reported that isoeugenol (the active ingredient in AQUI-S^TM) exposed male mice showed clear evidence of carcinogenicity, therefore efforts within the U.S. Department of Interior to develop AQUI-S^TM as a sedative that allows for immediate release ceased. Despite the ruling, AQUI-S^TM still has the potential to be approved as an anesthetic with a short withdrawal time. Among the data required to gain approval for use in the U.S. are data describing the composition and depletion of all AQUI-S^TM residues from fish fillet tissue. A total residue depletion study for AQUI-S^TM was conducted by exposing market-sized rainbow trout, Oncorhynchus mykiss (mean weight, 502.7 ± 54 g; s.d.) to 8.9 mg/L of ¹⁴C-[URL]-isoeugenol for 60 min in 17 °C water. The ¹⁴C-[URL]-isoeugenol was mixed with a surfactant resulting in a mixture that mimicked AQUI-S^TM. Groups of fish (n = 6) were sampled immediately after the exposure (0-h sample group) and at 0.5, 1, 2, and 4 h thereafter. Total isoeugenol-equivalent residue concentrations in the fillet tissue were determined by oxidizing triplicate subsamples of homogenized skin-on fillet tissue from each fish to ¹⁴CO₂ and enumerating the radioactivity by static liquid scintillation counting. Isoeugenol concentrations in fillet tissue were determined by extracting homogenized fillet tissue with solvents and determining the isoeugenol concentrations in the extracts with high performance liquid chromatography techniques. The mean total isoeugenol-equivalent residue concentrations in the 0, 0.5, 1, 2, and 4-h sample groups were 55.4, 32.0, 19.8, 11.3, and 4.9 µg/g, respectively. The primary chemical residue in fillet tissue from all exposed fish was isoeugenol. The mean isoeugenol concentrations in the 0, 0.5, 1, 2, and 4-h sample groups were 48.9, 26.5, 15.3, 7.2, and 2.2 µg/g, respectively. The percents of the total radioactivity classified as isoeugenol in the 0, 0.5, 1, 2, and 4-h tissue extracts were 95, 73, 73, 64, and 48%, respectively.     

The dynamics of Themeda Triandra tillers in relation to burning in the natal Drakensberg

Abstract

Marked tillers of Themeda triandra were sampled regularly over a two year period in Highland Sourveld burnt annually in winter, biennially in spring and after a single summer and early winter burning treatment. Parameters recorded were height of shoot apex, tiller mass, number of new lateral tillers and time of flowering. Monitoring of marked tillers before and after each burn enabled the life history of populations of tillers to be followed.

There were no significant differences in survivorship between tillers in the annual winter and biennial spring burn treatments but winter burning stimulated the development of a greater number of daughters per parent. Both populations exhibited a constant death rate over the two year period. Only 8% of the marked T. triandra tillers survived the single summer burning treatment.     

Aspects of the biology of three benthic-feeding teleosts from King’s Beach,Algoa Bay

The lengths, abundance patterns and feeding habits of three species of benthic-feeding teleosts, Lithognathus mormyrus, Lithognathus lithognathus and Umbrina capensis from King’s Beach, Algoa Bay are presented. Multiple regression analysis was used to elucidate the influence of the physical environment on the abundance of L. mormyrus. The feeding habits of these species were analysed on a quantitative basis by means of gravimetry and the frequency of occurrence of prey items.     

Observations on the reproductive cycles of Cellana capensis (Gmelin, 1791) and Patella concolor Krauss, 1848 (Gastropoda: Prosobranchia: Patellidae)

The reproductive periodicities of the patellid limpets Cellana capensis and Patella concolor were determined from changes in macro-and microscopic appearance of the gonads over a 14-month period. Both species appear to have protracted breeding periods with several peaks in spawning activity. Problems encountered with the application of standard sampling and analytical methods to species with such cycles are discussed.     

Characteristics of mature oocytes from four species of marine teleosts

The morphology and histology of the digestive tract of the branchiuran crustacean, Chonopeltis australis Box shall, 1976 are described from serial sections. The foregut is differentiated into a preoral cavity, containing the mandibles and tongue, an ascending oesophagus, with an H-shaped lumen invested with longitudinal, circular and dilator muscles, a horizontal oesophagus with a star-shaped lumen and lacking longitudinal and dilator muscles, and an oesophageal funnel consisting of inner and recurrent walls. The midgut is differentiated into anterior and posterior chambers, separated by an S-shaped muscular tube. The arborescent midgut glands open laterally into the anterior part of the anterior midgut. Columnar epithelial cells line the anterior midgut whereas tall, papilliform cells are present in the epithelium of the posterior midgut. The transition from posterior midgut to hindgut is marked by the presence of very tall epithelial cells. The terminology describing the various parts of the digestive tract of branchiurans is discussed.     

The prevalence of Proctoeces (Trematoda: Fellodistomidae) metacercarial infections in the brown mussel Perna perna (Bivalvia: Mytilidae) around the southern African coast

Unencysted trematode metacercariae of the genus Proctoeces were found embedded in the mantle tissue and visceral mass of the intertidal mussel Pema pema. Data on the prevalence and intensity of infection in southern African populations of Pema are presented. Results from a geographic survey indicated that Proctoeces infections were more prevalent in the region Port Elizabeth to Isilaka. At the majority of sites both prevalence and intensity of infection increased in conjunction with host size. Detailed studies of mussels from Dwesa failed to show seasonal changes in metacercarial infection. A strong relationship, however, was found between sex of host and parasitic infection, with female mussels harbouring the most metacercariae. The most heavily infected mussels examined came, ironically, from two nature reserves situated on a stretch of coastline where otherwise unprotected mussel stocks are subjected to intense exploitation by man. The possible pathogenic effects of Proctoeces on such highly stressed mussel populations clearly merits further attention.