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Alexis K. Nagel, Hetal Kalariya, and Guido Schnabel

The Gastrodia antifungal protein (GAFP-1) is a monocot mannose-binding lectin found in the Asiatic orchid Gastrodia elata. Transgenic plum (Prunus domestica var. ‘Stanley’) lines (4J and 4I) expressing GAFP-1 exhibit enhanced disease resistance to the stramenopile pathogen Phytophthora cinnamomi and the root-knot nematode Meloidogyne incognita. Rootstocks created from such transgenic lines might be more readily accepted by consumers if it can be shown that foreign gene products are not migrating into a grafted, nontransgenic scion on which fruit is produced. In this study, wild-type (WT) plum tissue was budded onto transgenic plum lines 4J and 4I to create chimeric-grafted trees. Tissues from chimeric-grafted trees were analyzed for gafp-1 transcripts (leaf and root) and protein (leaf, soft shoot, and root) by reverse transcription–polymerase chain reaction and immunodetection, respectively. Transcripts of gafp-1 were detected consistently in the root tissues but not within the leaves of the grafted, WT scions. Similarly, the GAFP-1 lectin was identified within the roots, but not in the soft shoot or leaf tissues of the grafted, WT scions. These results suggest that gafp-1 mRNA and protein are not moving into the WT scion tissues of chimeric-grafted plum trees.

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Alexis K. Nagel, Guido Schnabel, Cesar Petri, and Ralph Scorza

The Gastrodia antifungal protein (GAFP) is a monocot mannose-binding lectin isolated from the Asiatic orchid Gastrodia elata. This lectin has previously been shown to provide increased resistance in transgenic Nicotiana tabacum against taxonomically unrelated root pathogens Phytophthora nicotianae, Rhizoctonia solani, and Meloidogyne incognita, but its potential to confer disease resistance in tree species is not known. Agrobacterium tumefaciens-mediated transformation yielded three gafp-1 expressing plum lines (Prunus domestica) designated 4J, 4I, and 5D. These lines possessed one, two, and four copies of the gafp-1 gene, respectively, as demonstrated by DNA blotting. Lines 4J and 4I were not phenotypically different from the nontransformed control line, but line 5D showed significant divergence in leaf morphology and growth habit. Compared with the inoculated control line, lines 4J and 4I exhibited increased tolerance to Phytophthora root rot (PRR) caused by P. cinnamomi. When inoculated with the root-knot nematode, Meloidogyne incognita, the 4J and 4I lines showed a significantly lower degree of root galling than the inoculated control line. Nematode reproduction, as measured by the presence of egg masses and the number of eggs produced per gram fresh root, was significantly reduced in line 4J compared with the inoculated control line. The results of this study suggest that the expression of gafp-1 in the roots of a woody plant may confer some level of resistance to PRR and root-knot nematode. Long-term field trials will be necessary to confirm this hypothesis.

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Andrew P. Nyczepir, Alexis K. Nagel, and Guido Schnabel

The expression of gastrodianin antifungal protein (GAFP) in a form of its VNF isoform increases tolerance to Phytophthora root rot (Phytophthora cinnamomi) and the root-knot nematode (Meloidogyne incognita) in transgenic plum lines. However, nothing is known about the potential of the GAFP lectin to confer disease resistance to the ring nematode, Mesocriconema xenoplax, in plum. Three transgenic plum lines (4I, 4J, and 5D) expressing gafp-1 under the control of CaMV 35S promoter sequence were evaluated for their response to M. xenoplax in the greenhouse. All plum lines were rated as hosts of M. xenoplax. Among the individual plum lines tested, the number of M. xenoplax per gram of dry roots was lowest in the rhizosphere of transgenic line 5D, intermediate in that of the nontransformed control line, and greatest in line 4J. The results of this study indicate that the comparisons of the final soil densities (Pf) of adult and juvenile M. xenoplax expressed as nematodes per gram of dry roots provide a better measure of the nematode carrying capacity by the tested lines than Pf values referred to as number of M. xenoplax/100 cm3 soil.