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The tomato gene Mi-1.2 confers resistance against root-knot nematodes and some isolates of potato aphid. Resistance to the whitefly Bemisia tabaci previously has been observed in Mi-bearing commercial tomato cultivars, suggesting that Mi, or a closely linked gene, is responsible for the resistance. The response of two biotypes of B. tabaci to tomato carrying the cloned Mi was compared with that of the isogenic untransformed tomato line Moneymaker. Our results indicate that Mi-1.2 is responsible for the resistance in tomato plants to both B- and Q- biotypes. Mi-1.2 is unique among characterized resistance genes in its activity against three very different organisms (root-knot nematodes, aphids, and whiteflies). These pests are among the most important on tomato crops worldwide, making Mi a valuable resource in integrated pest management programs.
Additional keywords: Bemisia argentifolii, Macrosiphum euphorbiae, Meloidogyne spp., Mi gene, plant resistance, transgenic plants.
Plants have evolved sophisticated mechanisms to perceive biotic stresses caused by potential pathogens, and to translate that perception into an adaptive response (Dangl and Jones 2001). Plant resistance, mediated by specific genes, is included among the methods for biological control of pests and diseases (Gabriel and Cook 1990; Whitehead 1998), which is considered one of the most significant approaches to plant health management currently and in the near future (Cook 2000).
Whiteflies are major pests of both greenhouse and open-field horticultural crops. The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) causes severe damage to commercial tomato Lycopersicon esculentum L. worldwide. Two biotypes of B. tabaci, which differ in their pattern of random amplified polymorphic DNA polymerase chain reaction (PCR), have been described in Spain (Guirao et al. 1997): the B-biotype, identical to B. argentifolii Bellows & Perring from California, and the Q-biotype, whose populations lately are increasing in southern Spain. Damage by B. tabaci is caused directly through phloem feeding and indirectly by the transmission of 100 different plant viruses to a wide range of plants in tropical and subtropical zones. Tomato yellow leaf curl viruses (TYLCVs), which constitute one of the most important groups of geminiviruses, are transmitted by B. tabaci (Bedford et al. 1994; Blua and Toscano 1994; Brown 1994; Brown and Bird 1992, 1996; Carnero et al. 1990; Markham et al. 1996; Moriones et al. 1993; Schuster et al. 1996).