African Plant Protection - latest Issue

Citrus green mould, caused by Penicillium digitatum, is a serious postharvest disease which affects oranges during storage and in transit. The disease is mainly managed by application of postharvest fungicides. Some plant extracts have been shown to effectively inhibit P. digitatum growth. The aim of the study was to determine the efficacy of methanolic extracts of Monsonia burkeana and Euphorbia ingens on P. digitatum growth and citrus green mould severity under laboratory conditions. M. burkeana and E. ingens samples were collected from Sekhukhuni district in Limpopo, dried under shade and extracts were prepared using methanol. The final extract powder was used to amend growth medium and to prepare a water-based spray for artificial fruit infection. Both tested plant extracts inhibited P. digitatum growth in vitro. All concentrations of E. ingens had an equally significant effect on the pathogen growth when compared with the control. M. burkeana concentrations displayed varying suppressive effect on pathogen growth. Extracts of both plants were also able to significantly reduce disease severity in artificially infected citrus fruits when compared with the control. In conclusion, these results showed both extracts of M. burkeana and E. ingens had suppressive effects against P. digitatum.

The relative seasonal abundance of indigenous heteropterans occurring on Litchi chinensis Sonn. was studied in the Mpumalanga province of South Africa. Litchi appears to be a good host for these insects as 669 individuals from 22 species were recovered during the study period lasting approximately 15 months. The coconut bug Pseudotheraptus wayi Brown was not the dominant stink bug as was expected, but rather Coenomorpha nervosa Dallas and Pseudatelus raptorius (Germar) which represented nearly 80% of the individual insects that were recovered. Not only were these two species numerically dominant, they were also the only species that were able to breed in this crop. Additionally, both species were also abundant when fruit was available on the trees. None of the other heteropterans were able to breed in litchis as only adults were recovered. These insects also occurred in low numbers and were abundant during autumn and winter when no fruit were available on the trees. This implies possible competitive displacement of lesser important heteropterans by C. nervosa. Damage previously ascribed to P. wayi may actually be caused by C. nervosa and possibly P. raptorius. P. wayi overwintered on litchis and could be controlled on this crop during this time in order to reduce their impact in adjoining alternative subtropical fruit tree hosts.