ABSTRACT

 This research was on the evaluation and control of some pathogenic organisms of sweet potato tuber rot in storage using plant extracts. The study was carried out carried out to test the efficacy of some plant extracts and' to evaluate the preferred method of storage for the control ofAspergillus niger, Botryodiplodia theobromae and Rhizopus stolonifer. The rotcausing organisms were isolated from rotted tissues of sweet potato tubers obtained from Umudike in Umuahia Abia State, Nigeria. The evaluation ofdifferent storage methods were for ash, crate, grass and sand storage and it was a complete randomized design (CRD). The extracts used were obtained from leaves, seeds and bulbs ofAzadirachta indica, Jatropha curcas, Piper guinensis and Allium sativum respectively. Extracts of the four test plant materials were said to be fungitoxic against' test pathogens, while some of the storage methods helped to prevent these test pathogens from causing total rot on sweet potato tubers during the experimental period. From the results of statistical analysis, different storage methods proffered the growth inhibition of these organisms. Ash storage method was the most effective of all with an average of 71.16% and it affected the growth rate of B.theobromae on sweet potato tubers with incidence and severity rates of 68.30% and 6.33 more than A.niger: 74.70% , 6.77; Rstolonifer: 85.50%, 7.55 respectively. This was followed by Sand storage method which had an average of 80.13% with incidence and severity rates of 70.20% and 6.50 on the growth rates of B.theobromae. The values for others were A.niger: 80.90%, 6.88 and Rstolonifer: 89.30, 7.33 respectively. Grass and crate storage methods were the least effective in controlling these rot organisms on tubers of sweet potato. Water extracts of A.indica and J.curcas were found to possess the potentials for controlling the growth rate ofrot organisms ofB.theobromae and Rstolonifer on sweet potato tubers during the period ofstorage. A.indica was able to control the growth rates ofB. theobromae and Rstolonifer up to the 18lh day with severity of 4.66 and 4.25 at p=0.05 levels of probability, and was best when compared with other plant extracts evaluated. This result was followed closely by J.curcas with severity of 4.91 and 4.86 at p=0.05 levels of probability for B.theobromae and Rstolonifer respectively, at the 18th day of storage. The extracts with least inhibitory effects on growth rates ofthese rot organisms were Asativum and P.guinensis, they effected a varying degree of control but differed significantly from the results ofA.indica and J.curcas. Ash and sand methods of storage showed marked superiority over other storage methods in checkmating rot developments in sweet potato tubers during the period ofstorage, and are considered to be more affordable and relatively available to local farmers for effective control ofA.niger, B.theobromae and Rstolonifer during storage. Also leaf extracts ofA.indica and J.curcas could be used in the control ofB.theobromae and Rstolonifer which causes rot in sweet potato during storage.