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Key messageCarrizo transgenic plants overexpressing methionine-gamma-lyase produced dimethyl sulfide. The transgenic plants displayed more resistance to nematode attacks (Tylenculus semipenetrans) and may represent an innovative strategy for nematode control.Abstract Tylenchulus semipenetrans is a nematode pest of many citrus varieties that causes extensive damage to commercial crops worldwide. Carrizo citrange vr. (Citrus sinensis L. Usb × Poncirus trifoliate L. Raf) plants overexpressing Brevibacterium linens methionine-gamma-lyase (BlMGL) produced the sulfur volatile compound dimethyl sulfide (DMS). The aim of this work was to determine if transgenic citrus plants expressing BlMGL showed increased tolerance to T. semipenetrans infestation and to determine the effect on the content of key amino acids. While transgenic lines emitted dimethyl sulfide from leaves and roots, no sulfur-containing volatiles were detectable in wild-type Carrizo in the same tissues. Significant changes detected some key amino acids from leaves of transgenic plants such as aspartate, lysine, glycine, leucine and threonine with no changes in the amounts of methionine and α-ketobutyrate. In roots only glycine showed significant changes across all transgenic lines in comparison to wild-type plants. Transgenic plants expressing BlMGL and emitting DMS had less T. semipenetrans aggregation and more biomass than infected WT control plants, indicating that they may represent an innovative management alternative to pesticide/nematicide-based remedies.Electronic supplementary materialThe online version of this article (doi:10.1007/s11103-017-0666-9) contains supplementary material, which is available to authorized users.

Nematode-free micropropagated o wn-rooted English cultivars 'Vina' and 'Chandler' and seedling rootstocks Northern California black (NCB) and Paradox hybrid were planted into a 0.5 m 3 hole of sandy loam soil containing 100 Pratylenchus vulnus and two Meloidogyne incognita per 250 cm 3 of soil volume. Trees were farmed using micro-sprinkler irrigation with a 3 m by 4 m plant spacing. Trees were removed from the field site after 7 months and all new root growth partitioned into three size groupings including fleshy root tips, secondary roots (<7 mm diameter), and primary roots (>7 mm diameter). These two nematodes preferred the fleshy root tips supporting 172, 293, 369 and 882/gram of root on NCB, Paradox, 'Vina', and 'Chandler', respectively. Secondary roots supported 22, 117, 204 and 239/gram of root on NCB, Paradox, 'Vina', and 'Chandler', respectively. Few nematodes were present in primary roots although these roots were produced in the presence of inoculum. All Juglans spp. tested were susceptible or highly susceptible to P. vulnus. NCB was a poor host and non-galled by M. incognita, Paradox was intermediate, and the two J. regia cultivars proved susceptible. When present, the root knot galls were normal-sized and occurred across the root system, but never on the fleshy root tips. Paradox and J. regia cultivars occasionally developed 3 to 5 cm diameter galls on their secondary roots. Planting into high populations of these nematodes can greatly restrict early root exploration by Juglans spp. Total tree biomass at termination of the experiment ranged from 3.9 kg/tree for the more vigorous Paradox to 2.3 kg/tree for own-rooted 'Vina'. This difference was significant at P = 0.05 with other growth differences being intermediate and non-significant.

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