Monitoring Tomato Root Microorganisms

Root diseases pose a serious threat to tomato production with occasional severe outbreaks in the UK in recent years affecting both soil and hydroponic crops. Early identification of pathogens and an increased understanding of rhizosphere microbial populations could increase opportunities to manage root diseases more effectively. Two molecular methods were used to investigate root microorganisms in commercial tomato crops. During 2009 and 2010, samples of young roots from 20 long-season crops grown on their own roots (except soil crops) were examined by T-RFLP. Over 80 fungal and oomycete taxa were detected with Colletotrichum coccodes, Fusarium spp., Plectosphaerella cucumerina and Pythium spp. occurring at a high frequency. Microbial population diversity differed significantly with plant age and growing medium. In 2013 a microarray developed for detection of 75 fungal, oomycete and bacterial species previously recorded on tomato roots was used to regularly monitor root microbial populations in parallel with visual assessment of crop health. Root samples from three tomato crops grown on a Maxifort rootstock on rockwool slabs were examined every 2-3 weeks. The total number of taxa detected ranged from 26-42, with more diverse populations on sites where irrigation solution was recycled. Some fungi and oomycetes were very common in all crops on all sample occasions; others did not occur until many weeks after planting, others occurred at one site only. Despite the presence of several root-infecting pathogens, none of the three crops developed wilting, yellowing or other symptoms of poor growth commonly associated with root disease. These results suggest that tomato crops grown on a Maxifort rootstock can tolerate a level of root infection by some fungal and oomycete pathogens.