Analysis of resistance in tomato and sweet pepper against the greenhouse whitefly using electrically monitored and visually observed probing and feeding behaviour

Different types of plant resistance against the greenhouse whitefly, Triale urodes vaporariorum, were distinguished according to the tissue location of the resistance factors. The effects of resistance factors were compared by measuring the electrically monitored and visually observed probing and fee ding behaviour of whiteflies on two resistant tomato genotypes (82207 and 8 2216), a susceptible tomato cultivar, and a non-host plant, sweet pepper. O n sweet pepper, whiteflies displayed very short first probes, very long pat hway probing and spent much time on non-feeding activities such as walking and standing still. Also, a high percentage of whiteflies rejected sweet pe pper without ingesting substances from the phloem vessel. These data sugges t a strong resistance that is based on the factors present in surface/epide rmis and/or mesophyll layers of this plant. The behaviour of whiteflies on tomato 82207 was very different from that on sweet pepper. On tomato 82207 whiteflies apparently did not perceive resistance factors on the leaf surfa ce and in the mesophyll. Resistance factors appeared to be present in the p hloem tissue, because a higher number of phloem phases, longer phloem saliv ation periods and shorter phloem ingestion periods were observed when compa red with the susceptible tomato cultivar. Tomato 82216 showed no clear resi stance factor in the phloem. The importance of combined EPG and behavioural research for host-plant resistance studies are discussed.