Fusarium species associated with damping-off of rooibos seedlings and the potential of compost as soil amendment for disease suppression

Fusarium species associated with damping-off of rooibos in the Western Cape Province of South Africa were recovered from 12 nurseries during the 2007 to 2009 seasons. All 121 isolates obtained, morphologically resembled Fusarium oxysporum. Of the 58 representative isolates identified through sequence analyses of the EF-1α gene area, 25 were F. foetens and 33 F. oxysporum, and these two species were obtained from 11 and 12 of the nurseries, respectively. Two strongly supported clades (Clades 2 and 3) of the Fusarium oxysporum species complex were recovered in this study, while a well-supported clade corresponded to the clade reported as F. foetens. Twenty isolates of each Fusarium sp. were evaluated for their ability to cause damping-off of rooibos, and the rotation crops, lupin and oat, under glasshouse conditions. Both Fusarium spp. caused significant damping-off of rooibos seedlings, but not of lupin or oat. However, both species could be reisolated from lupin, but not from oat. This is the first report of these two Fusarium spp. as pathogens of rooibos seedlings, and also the first report of F. foetens in South Africa. Two commercial composts (compost A and compost B) from independent suppliers were evaluated for disease suppression under glasshouse conditions. Both composts significantly suppressed damping-off caused by both Fusarium spp., but in a few instances, compost B was more effective than compost A in disease suppression of individual isolates of both species.