RESUMO
BACKGROUND AND OBJECTIVE: Regeneration of plant through tissue culture technique is a critical process in transformation of plants. This study sought to establish the effect of genotype and auxin concentration on callus induction from different sweet sorghum genotypes (IESV92008DL, IESV92001DL, IESV92021DL, ICSV700 and ICSV93048). MATERIALS AND METHODS: In this study, MS medium supplemented with five levels of the hormone 2,4-D (0, 1, 2, 4 and 6 mg L-1) to assess the effect of the hormone 2,4-D on callus induction and regeneration was used. RESULTS: The highest callus induction frequency was observed at 2 mg L-1 2,4-D for all the genotypes, IESV92008 gave the highest callus induction frequency among all the genotypes at 2 mg L-1 2,4-D. The lowest callus induction frequency was observed 0 and 6 mg L-1 for all the genotypes, the two genotypes ICSV700 and IESV92021 were observed to give the lowest callus induction frequency among all the genotypes used in this study. Embryogenic callus induction frequency was observed to be higher at 2 mg L-1 2,4-D and the genotype IESV92008 gave the highest callus induction frequency among all the genotypes used. Induction of shoots was achieved in MS medium supplemented with 3 mg L-1 6BA and 1 mg L-1 IAA, the highest regeneration efficiency was obtained from the three genotypes ICSV93048, IESV92008 and IESV92001, respectively. CONCLUSION: This study discovers the importance of the auxin 2,4-D on callus induction and regeneration of sweet sorghum and this will help the researcher to develop protocols for transformation of sweet sorghum.
RESUMO
KEY MESSAGE: We report success of host-induced gene silencing in downregulation of aflatoxin biosynthesis in Aspergillus flavus infecting maize transformed with a hairpin construct targeting transcription factor aflR. Infestation of crops by aflatoxin-producing fungi results in economic losses as well as negative human and animal health effects. Currently, the control strategies against aflatoxin accumulation are not effective to the small holder farming systems in Africa and this has led to widespread aflatoxin exposure especially in rural populations of sub-Saharan Africa that rely on maize as a staple food crop. A recent strategy called host-induced gene silencing holds great potential for developing aflatoxin-resistant plant germplasm for the African context where farmers are unable to make further investments other than access to the germplasm. We transformed maize with a hairpin construct targeting the aflatoxin biosynthesis transcription factor aflR. The developed transgenic maize were challenged with an aflatoxigenic Aspergillus flavus strain from Eastern Kenya, a region endemic to aflatoxin outbreaks. Our results indicated that aflR was downregulated in A. flavus colonizing transgenic maize. Further, maize kernels from transgenic plants accumulated significantly lower levels of aflatoxins (14-fold) than those from wild type plants. Interestingly, we observed that our silencing cassette caused stunting and reduced kernel placement in the transgenic maize. This could have been due to "off-target" silencing of unintended genes in transformed plants by aflR siRNAs. Overall, this work indicates that host-induced gene silencing has potential in developing aflatoxin-resistant germplasm.
