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Title: TRANSGENIC SUGAR BEET CLONES CARRYING ANTIMICROBIAL GENES ARE MORE SUSCEPTIBLE TO CERCOSPORA LEAF SPOT DISEASE THAN THE REL-1, THE PARENT GENOTYPE

Author
item Kuykendall, Larry

Submitted to: Current Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cercospora-induced leaf spot disease is a devastating problem in sugar beet production throughout most of the U.S. growing areas. Recently, researchers developed sugar beets that carry genes from barley and potato that are important for resisting microbial attack. However, when two of these new genotypes and their parent germplasm were evaluated for Cercospora leaf spot resistance, they were more susceptible. Clearly, more research is needed. The results will be of interest to everyone working to improve disease resistance crops.

Technical Abstract: The relative susceptibility to Cercospora leaf spot of two different transgenic Beta vulgaris genotypes and their parent REL was tested under both high humidity and temperature in a plant-growth chamber. The two new transgenic clones were OOT that carries both the potato osmotin and the barley a-thionin genes each controlled by an osmotin promoter, and OP2, carrying the pathogenesis protein S gene also controlled by the osmotin promoter. These transgenics, along with the parental line Rel-1 (hereafter REL) for comparison, were infected with Cercospora beticola, and disease progression was quantified at 3 weeks post-infection in terms of both the number of lesions and the area of necrosis. Cercospora leaf spot lesions per leaf on each of the two transgenic sugar beet clones tested were significantly more numerous compared with the number formed on the parental genotype. Moreover the area of necrosis on leaves of genotypes OP2 and OOT was 30- and 200-fold larger, respectively, compared with the area of necrosis on infected leaves of REL. The presence of introduced chimeric genes encoding antimicrobials reduced rather than increased Cercospora resistance in these particular transgenic sugar beets. Either gene silencing or somoclonal variation can be considered as possible explanations.