Douglas Powell

Reduced PAL gene suppression in Verticillium-infected resistant tomatoes

In tomato, resistance to the wilt fungus Verticillium albo-atrum is determined primarily by the Ve locus. When two tomato near-isolines which differ at this locus and in their susceptibility to the pathogen were compared, more rapid suberin coating in the xylem of resistant plants correlated closely with a more rapid increase in the activity of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), an enzyme which is essential to the suberization process. In contrast, levels of mRNA did not increase proportionally to the measured enzyme activities; rather, there was a substantial suppression of mRNA levels in the susceptible tomato line, consistent with a much lower elevation of PAL activity and significantly less vascular coating. The suppression was absent or substantially reduced in the resistant line. The results indicate that the pathogen can suppress defense genes in susceptible plants but suggest that their expression is altered in resistant hosts and that post-transcriptional regulation plays a significant role.

Time course of wall-coating secretion in Verticillium-infected tomatoes

Abstract Massive infusion of conidia of Verticillium albo-atrum induced synchronous secretion of vascular coating in the petiolar xylem vessels of tomato. Controls were infused with water. Light microscope quantification of samples taken at 6 h intervals (12–42 h) showed that the frequency of responding vessels in colonized petioles was consistently higher in a resistant (CR) than in a susceptible (CS) near-isoline. The response was initiated at 8–12 h post-inoculation in both CR and CS but developed differently. In susceptible plants secretion was delayed in colonized vessels but initiated in surrounding uncolonized ones suggesting that the immediate presence of the fungus has a suppressive effect. Further evidence for pathogen suppression was found in the observation that higher levels of coating induction can be stimulated in both isolines by similar inoculation with non-pathogenic root flora. It is proposed that the presence of the dominant allele at the Ve -locus confers resistance to a pathogen-produced suppressor of the coating response.

Food safety and the consumer – perils of poor risk communication

The potential for stigmatisation of food is enormous. Well-publicised outbreaks of foodborne pathogens and the furore over agricultural biotechnology are but two current examples of the interactions between science, policy and public perception. Current risk management research indicates that it is essential for risk managers to show that they are reducing, mitigating or minimising a particular risk. Those responsible must be able to effectively communicate their efforts and must be able to prove they are actually reducing levels of risk.The components for managing the stigma associated with any food safety issue involve the following factors:• effective and rapid surveillance systems;• effective communication about the nature of risk;• a credible, open and responsive regulatory system;• demonstrable efforts to reduce levels of uncertainty and risk; and,• evidence that actions match words.Appropriate risk management strategies, such as on-farm food safety programs, are essential to demonstrate to consumer...

The SPS Agreement: Addressing historical factors in trade dispute resolution

The World Trade Organization Agreement on the Application of Sanitary andPhytosanitary Measures (the SPS Agreement) isa product of international efforts to blendtrade liberalization with standards of publichealth protection. One of the aims of theAgreement is to facilitate the pre-emption andmanagement of food safety related tradedisputes. An examination of nineteenth-centuryand modern-day trade disputes illustrates howthe SPS Agreement is positioned to carry outthis remit. Historical research andcontemporary experience vindicate the Agreementas a necessary treaty to address severalfactors that influence food safety relatedtrade disputes: economic considerations, riskperception, and regulatory coordination.