Abstract
The Zimbabwean genotype TGR-1551 had been found to be resistant to Bemisia tabaci Genn. in previous studies. In order to have a better knowledge of this resistance and determine the most suitable character to evaluate the genetic resistance to B. tabaci, three whitefly life-parameters have been tested in a RIL population (F 7 ) derived from a cross between 'TGR-1551' and the susceptible Spanish cultivar 'Bola de Oro'. Plants of each parent, their F 1 and 62 RIL were grown in a greenhouse under natural conditions of whitefly infestation. In each plant, the number of adults of B. tabaci, ovoposition and number of empty pupal cases were recorded. Significant differences were found between parents for each whitefly life-parameter: TGR-1551 showed a high level of resistance whatever the parameter was considered, and 'Bola de Oro' behaved as highly susceptible to B. tabaci. The low number of adults and low ovoposition found on leaves of TGR-1551 suggested the presence of non-preference mechanisms in this genotype. In the F 1 population, the number of adult whiteflies and the ovoposition was similar to 'Bola de Oro', while the number of empty pupal cases was similar to the number found in TGR-1551. These results pointed to the existence of antibiotic mechanisms in the resistant genotype which impede B. tabaci to reach its adult stage. Highly significant differences among RIL were observed for the three parameters, mainly for the number of empty pupal cases, explaining the 43 % of the variance observed. Some RIL behaved like TGR-1551 and some like the F 1 , which suggested a different genetic control of antixenosis and antibiosis mechanisms in TGR-1551. Dominance effects seem to be involved in antibiosis, while antixenosis, measured as ovoposition, should be regulated by recessive factors. These results confirm the usefulness of the number of empty pupal cases in the selection of B. tabaci resistance and for genetic studies.
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