Application of marker-assisted selection for ahFAD2A and ahFAD2B genes governing the high-oleic acid trait in South African groundnut cultivars (Arachis hypogaea L.)

One of the major shortcomings in cultivated groundnut in South Africa is the short shelf-life of the product due to rancidity of the oil rich seeds. Polyunsaturated fatty acids are more susceptible to oxidation than mono-unsaturated residues. Thus, it would be preferable to adjust the oleic acid: linoleic acid ratio to a more favourable one. The high-oleic acid trait in groundnut was reported to be dependent on two homeologous oleoyl-PC desaturase genes, ahFAD2A and ahFAD2B. Breeding of new cultivars with this characteristic can be time-consuming and expensive when doing fatty acid analysis in every generation for selection of the progeny with the highest oleic acid: linoleic acid ratio. Marker-assisted selection was applied to the local groundnut breeding program with the utilization of real-time polymerase chain reaction (PCR). The inheritance of the high oleic trait was followed in the 4th backcross progeny and revealed that all combinations of the two genes were found, except the ol2ol2 homologous mutant. The highest oleic acid percentage was found in progeny with all four mutant alleles (ol1ol1ol2ol2).Keywords: High-oleic, real-time PCR, oleoyl PC desaturase, marker-assisted selectionAfrican Journal of Biotechnology Vol. 12(27), pp. 4283-428

Genetic diversity in South African maize (Zea mays L.) genotypes as determined with microsatellite markers

One thousand and forty three (1043) maize genotypes including white and yellow maize inbred lines as well as hybrids from the public germplasm collection were characterized with 80 microsatellite markers distributed throughout the genome. A total of 1874 alleles were amplified and used in the genetic diversity analysis. Principal coordinate analysis confirmed the geographical distribution of the breeding lines. Cluster analysis using Rogers distance measures placed the breeding lines in several clusters and corresponded well with known pedigrees. Lines with mixed origin were classified in separate clusters and duplicate entries in the collection were identified. These mixed lines could not be placed in known heterotic groups, but could rather be used to identify new groups to be used in the breeding program. The genetic distances determined in the study can be applied to plan a more focused breeding program.Keywords: Genetic distances, maize, microsatellitesAfrican Journal of Biotechnology Vol. 12(2), pp. 123-13

Plant-parasitic nematodes associated with weeds in subsistence agriculture in South Africa

Twenty-nine plant-parasitic nematode species belonging to 15 genera, as well as two fungus-feeding nematode genera and one species, were identified from soil and root samples of weeds collected from 67 localities situated in subsistence production regions of South Africa during a survey from 2005-2006. Of these, 16 nematode species from four genera were reported for the first time to infect or to be associated with weeds. The predominant endo- and semi-endoparasites identified both from soil and root samples were Meloidogyne species, Pratylenchus zeae, Helicotylenchus dihystera and Rotylenchus unisexus. Based on PCR technology, three Meloidogyne species, M. hapla, M. incognita and M. javanica, have been identified in roots of weeds sampled. Thirty weed species representing 26 genera were identified as hosts of Meloidogyne species, while 38 belonging to 35 genera were associated with various other plant-parasitic nematodes. Meloidogyne species were predominant in the roots of Chloris virgata, Cynodon dactylon and Amaranthus hybridus. The frequency of occurrence of Meloidogyne species, H. dihystera and R. unisexus was significantly and positively correlated with localities in terms of % clay and % silt. The same trend was evident for these three taxa in terms of rainfall, while the opposite was observed in terms of their frequency of occurrence and pH. Principal component analysis results substantiated the latter. It also suggested that all four predominant plant-parasitic nematode species tend to occur more frequently at localities where maize was mono-cropped as well as where maize and vegetables were planted in rotation. Cynodon dactylon, Cyperus rotundus, Datura stramonium, Tagetes minuta and Eleusine corocana had the highest frequency of occurrence of weeds sampled. Identification of weeds that maintain plant-parasitic nematodes, particularly Meloidogyne species, suggested that these pathogens can have a negative impact on crop production when not controlled timely and effectively. Copyright © Koninklijke Brill NV, Leiden, 2012.status: publishe