Some plants nurture soil bacteria that keep them healthy

THE bacteria which inhabit human beings, particularly the guts of those beings, have been found in recent years to be important for fending off disease. That something similar happens in other animal species is doubtless true as well. But work by Seon-Woo Lee at Dong-A University and Jihyun Kim at Yonsei University, both in South Korea, suggests that it is not only animals which benefit from such bacterial shielding. Their study, just published in , shows that plants do, too. And that may have important implications for agriculture.Crop plants of the nightshade family, such as potatoes and tomatoes, are susceptible to a soil bacterium called . This enters their roots and spreads through their water-transport systems, causing them to wilt. Infection is usually lethal; the disease costs potato farmers alone $1bn a year. Some apparently suitable plants, though, seem exempt from ’s attentions. In particular, a variety of tomato called Hawaii 7996 does not suffer from such bacterial wilt. Dr Lee and Dr Kim wondered if the explanation for this exceptionalism lay with other bacteria in the soil.