Abstract:
Guava wilt disease (GWD), caused by Nalanthamala psidii, is a serious disease occurring in the guava-producing
areas of the Mpumalanga and Limpopo provinces of South Africa. Two resistant guava rootstocks, TS-G1 and
‘TS-G2’, were developed by the ARC-ITSC in 1995. In 2009, a renewed outbreak of GWD was reported, which also
affected the resistant ‘TS-G2’ cultivar, placing the guava industry under threat again. The aim of this study was to
seek resistant guava selections by means of in vitro screening of guava seedlings and subsequently testing the
most promising selections in inoculation studies with N. psidii. A culture filtrate of N. psidii was used to screen
guava seedlings in vitro. Promising selections were multiplied in tissue culture, hardened-off and planted in bags
before inoculation with the GWD fungus in a shadehouse trial. The number of plants surviving nine months after
inoculation was recorded. Although none of the selections showed complete resistance, selection MS44 showed
some tolerance against the G2 isolate of the pathogen obtained from diseased ‘TS-G2’ trees, whilst selection MS70
showed some tolerance against the G1 isolate obtained from diseased TS-G1 trees. These selections were also
resistant to the original Fan Retief isolate of the pathogen.
