ABSTRACT
Histological studies were carried out to investigate the impact of some pathogenic organisms on infected cassava root after different periods of incubation. Cassava roots inoculated with Aspergillus niger, Rhizopus stolonifer, Aspergillus flavus, and Trichoderma viride showed progressive depletion of the starch grains in the cells and tissue maceration of the cassava root as the period of incubation increased. Cassava root inoculated with A. flavus showed tissue necrosis and slight fragmentation of the starch grains whereas, cassava tissues infected with A. niger showed tissue necrosis and general maceration of the starch grains within the tissue thereby creating empty spaces within the cells with no clear arrangement of the starch grains. Inoculation of the cassava tissues with R. stolonifer resulted in rapid loss of the starch grains and erosion of surrounding cell boundaries. Cassava tissue colonized by T. viride showed tissue necrosis and maceration of the starch grains. Healthy (uninoculated) cassava root tissue showed intact cells packed with large starch grains suggesting that in the host-parasite relationship, the pathogens established themselves inter and intracellularly in the parenchymatous cells of the cortex of the cassava root clearing them of starch grains, and resulting to poor yield and nutritional value of cassava and also economic loss.
ABSTRACT
Investigations were carried out on the use of the water and ethanolic extracts of Piper guineense, Ocimum graticimum, Casia alata, and Tagetes erecta in the management of postharvest deterioration of cassava root caused by Aspergillus flavus and Rhizopus stolonifer. Water and ethanolic extracts of the plant materials had significant differences (p≤0.5) in their rates of fungitoxicity on the pathogenic organisms. Water and ethanol extracts of C. alata and T. erecta respectively at 50% concentration gave the same highest radial growth inhibition of 80.20% on A. flavus in vitro followed by ethanol extracts of C. alata, O. graticimum, and P. guineense. The ethanolic extract of T. erecta at 50% concentration gave the highest inhibitory effect of 53.50% on R. stolonifer followed by ethanol extracts of C. alata, O. graticimum, and P. guineense whereas the least growth inhibition of 0.17% was recorded by aqueous extract of P. guineense on R. stolonifer. In vivo test of the plant extracts applied before and after inoculation with spore suspension (1x105 spores/ml of distilled water) of test fungi showed significant reduction in root rot incidence and severity. The lowest incidence and severity of cassava root rot of 16.5% and 1.45 respectively were recorded with T. erecta ethanol extracts applied before inoculation of A. flavus indicating that the extracts of the plant materials could be better used as protectant than eradicant in the control of post harvest fungal deterioration of cassava root. R. stolonifer showed stronger resistance to the extracts of the plant materials than A. flavus during pathogenesis in vivo.
ABSTRACT
Colletotrichum destructivum was isolated from infected seeds and pods of cowpea (Var. IAR-48) with typical symptoms of anthracnose disease. The fungus during the pathogenesis, reduced the protein, fat, ash, crude fibre, carbohydrate, calcium and phosphorus, and increased the amount of iron, sodium, zinc, magnesium and potassium in the infected seed and husk. The carbohydrate, protein and phosphorus contents in the healthy husk reduced from 55.05%, 11.21% and 171.85 mg to 39.94%, 8.92% and 42.92 respectively in the infected sample whereas potassium and sodium contents in the healthy pod increased from 1.03 mg and 78.29 to 2.90 mg and 100.65 mg respectively in the infected husk. The potassium, sodium, magnesium and iron increased from 1292.25 mg, 0.19 mg, 0.09 mg and 11.00 mg in the healthy seeds to 1536.03 mg, 0.28 mg, 0.21 mg and 13.19 mg respectively in the infected seeds. The fungus caused the depletion of phosphorus from 498. 06 mg in the healthy to 430.17 mg in the infected seed, protein from 24.09% to 17.86%, carbohydrate from 57.02% to 34.35%, fat from 1.70% to 1.33% and crude fibre from 3.94% to 2.61%. The average loss of the major nutrient values; protein, carbohydrate and fat were 28.95% and 22.55% for seed and husk respectively after 8 weeks of planting.