b'Spinach breeder Johan Rijk. Source: KWS Vegetables There is good news, however, says Bart Geraats, senior sci- banned, and crop rotation is also too narrow. Geraats also sees entist phytopathology (lettuce and spinach) at BASF, that newdamping off pathogens as currently problematic, especially now resistance sources have been introduced by breeding companies.that seed treatment possibilities have diminished. In addition, The increased variation of resistance genes counteracts the evo- Johan Rijk says that under specific conditions, leafspot-causing lution of new isolates that break resistances. Its thought thatpathogens are on the rise. the ability of the DM pathogen to overcome multiple resistanceIn the Stemphylium front, Johansen notes that several sub-genes at the same time comes with a fitness penalty, he says,species have been identified. Johan Rijk adds that using molecu-and thus such new isolates are believed to become less virulent.lar diagnostics, we can now observe that different subspecies of At Syngenta, resistance is being achieved by combiningexisting pathogens can cause similar disease phenotypes.resistant genes in hybrids. At BASF, besides routine screening of breeding material for all known DM races, the development of new races is continuously monitored on a global scale. In addi-tion, new ways of resistance testing are regularly investigated.MORE AND MORE, SOIL-PATHOGEN At KWS, says senior spinach breeder Johan Rijk, weRELATED PROBLEMS APPEAR IN work with different universities all around the globe to under-stand more and more about DM to try to unravel all its secrets.SPINACH. BECAUSE MORE ANDHopefully one day this knowledge will help us to find a longer- MORE SEED-TREATMENTS ARE term solution. At the moment, various techniques and scenarios are being investigated and checked, but its not easy nor obvious. BANNED, AND CROP ROTATION ISFarmers, adds Johansen, can also do their part to help con- TOO NARROW.trol DM. Improved rotation practice is in our view a pre-condi-tion to reduce the speed of new races appearing. Geraats says in addition, farmers should manage DM with an Integrated Pest Management approach. Kumari Sharma advises growers to plant a mixture of varieties with different resistance profiles to secureGENETIC DIVERSITY their crop but also to make it difficult for the pathogen to quicklyAccording to Kumari Sharma, spinach has a relatively narrow break the resistance. genetic diversity. She says almost all breeders hunt for new sources of resistance from wild germplasm/genebank materials, OTHER THREATSmaking it a level playing field. The differences in genetic diversity There are many other diseases of concern in this crop besideat various breeding companies, she says are about how long have downy mildew, notes Ben Hunter, lead of the Global Spinachyou been hunting and being able to enrich the genetic diversity Collaborative Breeding Pipeline Team at Bayer Crop Science.within your own program by other available methods. There are These include Colletotrichum, Cladosporium, Stemphylium,two wild spinach species, Spinacia turkestanica and Spinacia Fusarium, Pythium, white rust (Albugo occidentalis) andtetrandra, that are mainly used as new germplasm sources.Verticillium. Johan Rijk reports that samples of these species have been Johan Rijk reports that more and more, we see soil-path- collected by KWS during collection missions of the Dutch Centre ogen related problems such as damping-off caused by differentfor Genetics Resources (CGN), and his team also uses new tech-Pythium species, and root rot caused by Fusarium. Two ofnologies to discover new resistance sources and types. In Laans the reasons for this is that more and more seed-treatments areview, of the CGNs collecting missions of these wild species, the 28IEUROPEAN SEEDIEUROPEAN-SEED.COM'