Transfer of amiprophosmethyl resistance from a Nicotiana plumbaginifolia mutant by somatic hybridisation

Transfer of resistance to the phosphorothioamidate herbicide, amiprophosmethyl (APM), from the P-tubulin mutant of Nicotiana plumbaginifolia to the interspecific N, plumbaginifolia (+) N, sylvestris is and to the intertribal N, plumbaginifolia (+) Atropa belladonna somatic hybrids has been demonstrated. Transfer to the recipient species was accomplished by: (1) symmetric hybridisation and (2) asymmetric hybridisation using gamma-irradiation of donor protoplasts. Cytogenetic analysis confirmed the hybrid origin of the hybrids obtained. It was established that most of them typically inherited no more than three donor chromosomes, although it was possible to obtain symmetric hybrids in the case of symmetric fusion. Immunofluorescent microscopy analysis has shown that protoplasts of the mutant, and of the N. plumbagini-folia (+) N. sylvestris and N. plumbaginifolia (+) A. belladonna hybrids, retained the normal structure of interphase microtubule (MT) arrays and mitotic figures after treatment with 5 mu M APM, whereas MTs of protoplasts of the recipients were destroyed under these conditions. It was also shown that hybrid clones contained an altered beta-tubulin isoform originating from the N. plumbaginifolia mutant. The selected hybrid clones were characterised by cross-resistance to trifluralin, a dinitroaniline herbicide with the same mode of anti-MT action. Some of the somatic hybrids which could flower were fertile. It was established that seeds of some fertile hybrids were able to germinate in the presence of 5 mu M APM. The results obtained thus support the conclusion that the technique of somatic hybridisation, especially asymmetric fusion, can be used to transfer APM resistance from the N. plumbaginifolia mutant to different (related and remote) plant species of the Solanaceae, including important crops.

Exogenous RNA interference exposes contrasting roles for sugar exudation in host-finding by plant pathogens

Plant parasitic nematodes (PPN) locate host plants by following concentration gradients of root exudate chemicals in the soil. We present a simple method for RNA interference (RNAi)-induced knockdown of genes in tomato seedling roots, facilitating the study of root exudate composition, and PPN responses. Knockdown of sugar transporter genes, STP1 and STP2, in tomato seedlings triggered corresponding reductions of glucose and fructose, but not xylose, in collected root exudate. This corresponded directly with reduced infectivity and stylet thrusting of the promiscuous PPN Meloidogyne incognita, however we observed no impact on the infectivity or stylet thrusting of the selective Solanaceae PPN Globodera pallida. This approach can underpin future efforts to understand the early stages of plant-pathogen interactions in tomato and potentially other crop plants.