Lee A. Calvert

Morphological and mitochondrial DNA marker analyses of whiteflies (Homoptera : Aleyrodidae) colonizing Cassava and beans in Colombia

Abstract Morphology of the third antennal segment and compound eyes of adults of the whitefly species Bemisia tabaci (Gennadius), B. argentifolii Bellows & Perring, B. tuberculata (Bondar), Trialeurodes vaporariorum (Westwood), T. variablilis (Quaintance), and Aleurotrachelus socialis (Bondar) were studied using scanning electron microscopy to aid in identification of adult whiteflies in cassava and beans in Colombia. Random amplified polymorphic DNA polymerase chain reaction markers proved complementary to the morphological identification of whitefly species and the only rapid method to distinguish individuals in the Bemisia tabaci species complex. From each species of whitefly, a region of the mitochondrial 16S rDNA gene was amplified, cloned and the sequence determined. Parsimony and distance analyses were performed and the results were similar to those based on morphology. The distance between the two species of Trialeurodes was greater than expected for two species within the same genus. The combination of morphological and molecular traits is useful in understanding the diversity and evolution of these whitefly species.

Harmonizing the agricultural biotechnology debate for the benefit of African farmers

The intense debate over agricultural biotechnology is at once fascinating, confusing and disappointing. It is complicated by issues of ethical, moral, socio-economic, political, philosophical and scientific import. Its vocal champions exaggerate their claims of biotechnology as saviour of the poor and hungry, while, equally loudly, its opponents declare it as the doomsday devil of agriculture. Sandwiched between these two camps is the rest of the public, either absorbed or indifferent. Biotechnology issues specific to the African public must include crop and animal productivity, food security, alleviation of poverty and gender equity, and must exclude political considerations. Food and its availability are basic human rights issues—for people without food, everything else is insignificant. Although we should discuss and challenge new technologies and their products, bringing the agricultural biotechnology debate into food aid for Africa where millions are faced with life-or-death situations is irresponsible. Agricultural biotechnology promises the impoverished African a means to improve food security and reduce pressures on the environment, provided the perceived risks associated with the technology are addressed. This paper attempts to harmonize the debate, and to examine the potential benefits and risks that agricultural biotechnology brings to African farmers. Key words : Agriculture, biotechnology, biotechnology debate, biotechnology and Africa, biotechnology issues, food security, poverty alleviation. African Journal of Biotechnology Vol.2(11) 2003: 394-416

Differentiation of Bemisia tabaci (Genn.) (Hom., Aleyrodidae) populations in Colombia

We obtained evidence for genetic differentiation (detected by electrophoresis) of geographical populations of the whitefly, Bemisia tabaci (Genn.), in Colombia. The differences are undetectable by conventional taxonomic characters but are expressed at an esterase marker locus. There was no indication of host‐race formation.

Major QTLs control resistance to Rice hoja blanca virus and its vector Tagosodes orizicolus

Rice hoja blanca (white leaf) disease can cause severe yield losses in rice in the Americas. The disease is caused by the rice hoja blanca virus (RHBV), which is transmitted by the planthopper vector Tagosodes orizicolus. Because classical breeding schemes for this disease rely on expensive, time-consuming screenings, there is a need for alternatives such as marker-aided selection. The varieties Fedearroz 2000 and Fedearroz 50, which are resistant to RHBV and to the feeding damage caused by T. orizicolus, were crossed with the susceptible line WC366 to produce segregating F2:3 populations. The F3 families were scored for their resistance level to RHBV and T. orizicolus. The F2:3 lines of both crosses were genotyped using microsatellite markers. One major QTL on the short arm of chromosome 4 was identified for resistance to RHBV in the two populations. Two major QTL on chromosomes 5 and 7 were identified for resistance to T. orizicolus in the Fd2000 × WC366 and Fd50 × WC366 crosses, respectively. This comparative study using two distinct rice populations allowed for a better understanding of how the resistance to RHBV and its vector are controlled genetically. Simple marker-aided breeding schemes based on QTL information can be designed to improve rice germplasm to reduce losses caused by this important disease.