b'resistance genes, he says, there are less Bremia problems in growers fields than 20 years ago. Besides Bremia and Fusarium, Bejo focuses on breeding for resistance to bacterial diseases; Meridiem on pink rib, a virus disease called Lettuce Big Vein and the currant-lettuce aphid (Nasonovia ribisnigri); Rijk Zwaan on Lettuce Mosaic Virus (LMV), Nasonovia bacterial leaf spot and Big Vein. BASF and Syngenta focus on all of these diseases as well as Nasonovia. Prakash notes that although Nasonovia causes the most damage in the lettuce sector, multiple aphid species can attack the crop. The root-infecting aphid Pemphigus bur-sarius can cause significant losses in some lettuce markets, he explains. And, besides causing direct damage to the let-tuce plant, aphids can spread numerous Potyviruses such as LMV. LMV can also be transmitted from infected seeds into a new crop, and the presence of aphids can quickly multiply the number of infected plants.Prakash points to another group of viruses that can impact certain lettuce markets, the Tospoviruses, specifically Tomato Spotted Wilt Virus (TSWV) and Impatiens Necrotic Spot Virus (INSV). Although Tospoviruses are not seed-transmitted, they can be transmitted by thrips insects, he says. Among the bac-terial pathogens of lettuce, Pectobacterium carotovorum and Xanthomonas axonopodis pv. vitians can be considered rel-atively important. Whereas the first one can cause head rot or soft rot, X.a.vitians is the causal agent of leaf spot disease in lettuce. Splashing water from rain or overhead irrigation facili-tate disease spread and development.Maraldi seeds is a medium-small company, with quite young research and in the last 10 years we worked hard to be competitive and offer varieties with a strong package of resist-ances, says Zaccaria. Her company focused a lot on the intro-gression of resistance genes for the current main pathogens for baby lettuce, Bremia lactucae and Fusarium. Today Maraldi offers a wide range of baby lettuces with a full Bremia resistance (actually Bl:16-36EU) and we are working to increase the level of Fusarium tolerance in our materials both for race 1 and for the new one 4. Looking at the future surely, we want to improve and expand our resistances package, she adds. EMERGING THREATSNew threats to lettuce come from both new diseases and evolv-ing forms of existing pathogens. On the Fusarium front, Schut explains that the well-known Race 1 has spread more widely during the last two decades and is still the main race worldwide. However, Race 4 was foundLettuce Breeder Lisa Zaccaria. Source: Maraldi Sementifive years ago in the Netherlands, he says. It has spread, also to the neighbouring countries, and is causing problems mainly in indoor lettuce. We are introducing more and more varietiestance, it is important to continuously monitor for new disease with resistance against these races.occurrences. The impact of a disease in a crop can change as And, although resistance to Nasonovia was introduced ina result of new cultivation practices, increasing crop pressure lettuce varieties by Rijk Zwaan in 1997, in 2007 a new variantand reducing crop area, limitations in the use of crop protec-(biotype 1) appeared in Europe and broke through the resist- tion products such as seed treatments and fungicide sprays, and ance. This biotype is also causing problems in Australia andchanging climate conditions. Its therefore important to have California, Schut reports. Resistance to this new biotype wasnew disease symptoms always diagnosed by a phytopathology found in wild lettuce but is not yet available in cultivated let- specialist. tuce. Zaccaria says to address new pathogens/pests or new forms Although new races of existing diseases or the movementof existing ones, the research of new germplasm as source of of existing diseases to new geographic areas do happen withnew resistance genes is very important. Also, the research for lettuce, Prakash says appearance of completely new diseases ismolecular markers to speed up the selection of new resistance very uncommon. But it does happen, he says. For example, ingenotypes plays an important role, she notes. 2011 a new virus disease was discovered in lettuce which wasThere will be more information on how new techniques and named Lettuce Necrotic Leaf Curl Virus (LNLCV) of the genustechnologies are being used in lettuce breeding in the February Torradovirus. Until then, no Torradoviruses that can infect let- issue.tuce were known. Although this disease is not of major impor-EUROPEAN-SEED.COMIEUROPEAN SEED I 9'