Risk assessment of the entry of Pantoea stewartii subsp. stewartii on maize seed imported by the EU from the USA

Abstract

Following a request from the European Commission, the EFSA Panel on Plant Health performed a risk assessment of the entry of Pantoea stewartii subsp. stewartii on maize seed imported by the EU from the USA. This pest is a Gram-negative bacterium which causes Stewart's vascular wilt and leaf blight of maize (including sweet corn), a disease responsible for serious crop losses throughout the world. The following scenarios were considered: scenario A0 (current practice), scenario A1 (US request for modification of EU conditions for derogation), and scenario A2 (EU conditions for derogation). Results from the quantitative seed pathway model presented here show that, despite the low rates of plant-to-seed and seed-toseedling transmission that have been reported in the literature for Stewart's wilt, given the amount of traded seed, and in the case of voluntary (i.e. not mandatory) inspections of seed production fields at the origin (i.e. scenario A0), the frequency of introducing the disease is in the order of magnitude of some hundred introductions per year (median number). The EU conditions for derogation would lead to a decrease in the likelihood of entry compared to scenarios A0 (about 10,000 times fewer introductions) and A1 (about 2,000 times fewer introductions). This protective effect is mainly due to the requirement that only genotypes resistant to Stewart's wilt are traded, with the additional field inspection (two instead of one per season) providing additional reassurance. The Panel also concluded that seed lot inspections, as currently carried out (e.g. with a sample of 400 seeds) are not likely to lead to a relevant reduction in the level of infected imported maize seed, given the low prevalence of Stewart's wilt at the origin. If, however, there is aggregation in infection among consignments, inspection would work towards identifying the highly infected consignments. Recently, outbreaks of Stewart's wilt have occurred in Italy (Emilia Romagna, Friuli, Lombardy and Veneto). A review is provided of the available information to assess the possible role of seed imports in these outbreaks.

Risk assessment of Xanthomonas citri pv. viticola for the EU

“…The scenario with additional RROs (A2) was not called A1 to be consistent with previous EFSA PLH PRAS (e.g. EFSA PLH Panel, 2019b ), where A2 was the scenario with additional RROs, and A1 was the deregulation scenario.…”

Status and Recent Developments of Pantoea stewartii subsp. stewartii Causes the Wilt Disease in Maize in Indonesia: A Review

“…In addition to its widespread, Stewart's wilt seriously impacts the world economy. In the United States, this disease causes considerable losses to the sweet corn and seed industry (Bragard et al, 2019). These losses arise as a result of the sustainable use of sweet corn hybrid seeds known to be susceptible but planted in areas where there are vectors of the disease.…”

“…This information is evidence that vectors have a major role in spreading and conserving pathogens in nature. However, it is known that the spread of disease between countries and continents is more on movement through trade in source seeds (Bragard et al, 2019).…”

“…Wilt disease in maize seriously threatens sustainable food production and ecosystems worldwide (Strange and Scott, 2005;Bragard et al, 2019). Disease management is currently mostly done using synthetic materials.…”

Degree of certainty in scientific advice: implications for risk management and communication

“…As part of its commitment to transparency, the European Food Safety Authority (EFSA) has been developing improved approaches to assessing uncertainty and expressing the degree of certainty in its scientific outputs (EFSA Scientific Committee 2018a, 2018b, EFSA 2019 and is increasingly implementing them in its work, starting with the non-regulated areas.…”