b'Maraldi Sementis red baby leaf lettuce. rial pathogens of lettuce, Pectobacterium carotovorum andance against these races. Xanthomonas axonopodis pv. vitians can be considered relatively And, although resistance to Nasonovia was introduced in important. Whereas the first one can cause head rot or softlettuce varieties by Rijk Zwaan in 1997, in 2007 a new variant (bio-rot, X.a.vitians is the causal agent of leaf spot disease in lettuce.type 1) appeared in Europe and broke through the resistance. Splashing water from rain or overhead irrigation facilitate diseaseThis biotype is also causing problems in Australia and spread and development. California, Schut reports. Resistance to this new biotype was Maraldi seeds is a medium-small company, with quite youngfound in wild lettuce but is not yet available in cultivated lettuce.research and in the last 10 years we worked hard to be competi-Although new races of existing diseases or the movement tive and offer varieties with a strong package of resistances, saysof existing diseases to new geographic areas do happen with Zaccaria.lettuce, Prakash says appearance of completely new diseases is Her company focused a lot on the introgression of resistancevery uncommon. genes for the current main pathogens for baby lettuce, BremiaBut it does happen, he says. For example, in 2011 a new lactucae and Fusarium.virus disease was discovered in lettuce which was named Lettuce Today Maraldi offers a wide range of baby lettuces with aNecrotic Leaf Curl Virus (LNLCV) of the genus Torradovirus. full Bremia resistance (actually Bl:16-36EU) and we are workingUntil then, no Torradoviruses that can infect lettuce were known. to increase the level of Fusarium tolerance in our materials bothAlthough this disease is not of major importance, it is important for race 1 and for the new one 4. Looking at the future surely, weto continuously monitor for new disease occurrences. The impact want to improve and expand our resistances package, she adds. of a disease in a crop can change as a result of new cultivation practices, increasing crop pressure and reducing crop area, limi-Emerging Threats tations in the use of crop protection products such as seed treat-New threats to lettuce come from both new diseases and evolv- ments and fungicide sprays, and changing climate conditions. ing forms of existing pathogens.Its therefore important to have new disease symptoms always On the Fusarium front, Schut explains that the well-knowndiagnosed by a phytopathology specialist. Race 1 has spread more widely during the last two decades and Zaccaria says to address new pathogens/pests or new forms is still the main race worldwide. However, Race 4 was found fiveof existing ones, the research of new germplasm as source of years ago in the Netherlands, he says. It has spread, also to thenew resistance genes is very important. Also, the research for neighbouring countries, and is causing problems mainly in indoormolecular markers to speed up the selection of new resistance lettuce. We are introducing more and more varieties with resist- genotypes plays an important role.SWFEBRUARY 2021SEEDWORLD.COM /59'