Use of RNA interference and overexpression of purple acid phosphatase genes in management of parasitic plants
Alakonya, Amos E.
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Parasitic plants are major contributors to food insecurity in poverty stricken Sub Saharan Africa; To date, there is no effective parasitic plant control strategy that has been adopted by the majority of small scale farmers in the region leading to continued parasite spread and hence food insecurity. This study evaluated a variety of strategies against the parasitic plants Cuscuta pentagona, Striga hermonthica and Orobanche eaegyptica. The efficacy of RNA interference and intercropping with phosphorus efficient species was evaluated against C. pentagona and S. hermonthica. Further the effect of overexpressing purple acid phosphatases genes in tomato on 0. eaegyptica management was also evaluated. First, this study established that C. pentagona KNOX genes were involved in haustoria development. Targeting C. pentagona KNOX genes by interspecific RNA silencing through transgenic Nicotiana tabaccum as the host caused haustoria distortion and suppressed C. pentagona growth. Contrary to the results obtained in C. pentagona KNOX gene silencing study, targeting of the C. pentagona plasma membrane H+-ATPase through transgenic Medicago sativa did not suppress C. pentagona nor silence the H+ATPase gene. Instead, the parasite elicited a hypersensitive reaction and changed its mode of obtaining nutrients from symplastic to apoplastic transfer. In addition, this study showed that intercropping of maize with a P fixing legume Lupinus albus does not mobilize enough phosphorus in the rhizosphere for access by maize although it enhances cereal biomass accumulation and suppression of S. hermonthica emergence. Furthermore, it was shown that intercropping L. alb us and maize does not affect arbuscular mychorrhiza fungi colonization in maize roots. Of further interest was the confirmation that soil phosphorus level and arbuscular mychorrhiza fungi colonization have an inverse relationship in S. hermonthica tolerant and susceptible maize and sorghum cultivars evaluated. Finally, the overexpression of purple acid phosphatases from L. albus and Medicago truncatula in tomato resulted in low Orobanche emergence, enhanced root branching, improved tomato vigor and low arbuscular mychorrhiza fungi colonization. It was concluded that RNA interference, intercropping of maize with phosphorus efficient species like L. albus and overexpression of purple acid phosphatases from L. albus and M truncatula can reduce parasitic plant infestation and establishment. These findings lay the foundation for further studies in food crops like maize and Sorghum which have been greatly impacted by Striga.