norwich scientists are on the trail of（跟踪，追赶） some of the most economically damaging organisms that infect crops worldwide. their latest targets are the 1（寄生的） water 2 that causes powdery 3（白粉病） and the water molds（水霉） that cause late 4（枯萎病，荒芜） in potatoes and tomatoes and downy mildew（霜霉病） in cruciferous（十字花科的） vegetables and other crops. "we have been studying the late blight pathogen for a while," said professor sophien kamoun, head of the sainsbury laboratory on the norwich research park. "in separate research we are trialling plant 5 that 6 blight resistance, while in this latest study we have learnt more about how the pathogen itself evolved and which genes we should focus on to tackle it."
the scientists compared the genome of the potato blight pathogen to the genomes of four sister species that infect plants as diverse as morning glory and the 7 four o-clock. these closely related pathogens are from mexico, the centre of origin of the late blight pathogen.
the analysis showed that some sections of the genome are slow to evolve and are highly similar between the sister species. other sections are more dynamic and allow the pathogen to quickly jump hosts to infect and adapt to new plant species.
"our aim is to develop resistance to genes from the stable, slowly-evolving region of the pathogen's genome," said professor kamoun.
"this should be more disruptive to the pathogen's ability to evolve new races."
published in the same edition of the journal science are two studies focusing on 8. like the late blight pathogen, the 9 that causes downy mildew is a kind of water mold or oomycete. the oomycetes are fungal-like organisms that have evolved from 10 11. downy mildew causes yellow patches and fuzzy white mould on the leaves of many crops including crucifers, 12, grapes and 13. powdery mildew is a fungal disease of 14 that is most damaging in cool, wet climates.
"a major focus of our research is sustainable agriculture," said john innes centre director professor dale sanders.
"we need to help breeders and farmers generate good quality food and other agricultural products in an environmentally sustainable way. one way of doing so will be to develop crops that are 15 to pathogens and pests. such crops will reduce the need to spray 16 and fungicides and they will give better yields, as less will be lost to disease."
the genomes of the 17 have been sequenced in separate research collaborations, one involving john innes centre scientists and the other the sainsbury laboratory. the genomes were compared with those of closely related species.
analysis revealed that the parasites have discarded many genes. they have become specialised to live 18 on their plant host and have 19 with（免除，省掉） the genes that would be needed to survive elsewhere. instead they have focussed on genes that help them stealthily take control of host cells. the genome sequences reveal large numbers of effector proteins, the 20 that invade plant cells to suppress plant 21.
收听单词发音 
