Characterization of some fungal pathogens causing anthracnose disease on yam in Cross River State, Nigeria.

Yam anthracnose is one of the most serious fungal diseases affecting white and water yam production. Screening of available landraces for new sources of durable resistance to the pathogen is a continuous process. In the present study, the pathogens causing anthracnose in Dioscorea alata and Dioscorea rotundata farms in Cross River State yam belt region were characterized. Diseased yam leaves with anthracnose symptoms collected from the farms were used in the isolation, purification and, identification of C. alatae strains using morphological, cultural, and molecular methods. Leaf chlorosis, leaf edge necrosis, blights, dark brown to black leaf spots, shot holes, necrotic vein banding and vein browning were the predominantly observed symptoms. Seven isolates of C. alatae, Ca5, Ca14, Ca16, Ca22, Ca24, Ca32 and Ca34, and one isolate of Lasidioplodia theobromae, Lt1 were found to be associated with yam infection in Cross River State, with Lt1 as the most prevalent, occurring in all the locations. These isolates were classified into four forms which included the slow-growing grey (SGG), the fast-growing grey (FGG), the fast-growing salmon (FGS), and the fast-growing olive (FGO). Sequence analysis of the ITS region revealed <80% nucleotide identity between the isolates and the reference C. gloeosporioides. Pathogenicity test showed that all the isolates displayed typical symptoms of anthracnose disease as were observed in the field, but Lt1 was the most virulent. Inoculation of 20 D. alata and 13 D. rotundata landraces with isolate Lt1, showed that 63.64% of the landraces were susceptible while 36.36%were resistant. D. alata landraces were the most susceptible. This study revealed that anthracnose is prevalent and may assume an epidemic dimension in the yam growing communities of the state. There is need for increased effort in the breeding of yam for anthracnose resistance.

Strategies to combat the problem of yam anthracnose disease: Status and prospects.

Yam (Dioscorea spp.) anthracnose, caused by Colletotrichum alatae, is the most devastating fungal disease of yam in West Africa, leading to 50%-90% of tuber yield losses in severe cases. In some instances, plants die without producing any tubers or each shoot may produce several small tubers before it dies if the disease strikes early. C. alatae affects all parts of the yam plant at all stages of development, including leaves, stems, tubers, and seeds of yams, and it is highly prevalent in the yam belt region and other yam-producing countries in the world. Traditional methods adopted by farmers to control the disease have not been very successful. Fungicides have also failed to provide long-lasting control. Although conventional breeding and genomics-assisted breeding have been used to develop some level of resistance to anthracnose in Dioscorea alata, the appearance of new and more virulent strains makes the development of improved varieties with broad-spectrum and durable resistance critical. These shortcomings, coupled with interspecific incompatibility, dioecy, polyploidy, poor flowering, and the long breeding cycle of the crop, have prompted researchers to explore biotechnological techniques to complement conventional breeding to speed up crop improvement. Modern biotechnological tools have the potential of producing fungus-resistant cultivars, thereby bypassing the natural bottlenecks of traditional breeding. This article reviews the existing biotechnological strategies and proposes several approaches that could be adopted to develop anthracnose-resistant yam varieties for improved food security in West Africa.

Efficient elimination of Yam mosaic virus (YMV) from white yam (Dioscorea rotundata Poir.) by cryotherapy of axillary buds.

Dioscorea rotundata is an economically important food crop in many tropical countries as many people in this region depend on it for food and livelihood. Viral diseases, especially Yam mosaic virus (YMV), constitute a major constraint in the cultivation of this crop as they perpetuate through generations in the vegetatively propagated planting materials. Getting resistant or at least virus-free planting materials for farmers thus becomes crucial. This study was aimed at eliminating YMV in Dioscorea rotundata by cryotherapy of axillary buds. Enlarged axillary buds of YMV-infected TDr 2269 were frozen in liquid nitrogen for 1 h, re-warmed at 40 °C and cultured to regenerate plantlets. Approximately 76.33% plantlet regeneration and 100% YMV eradication were obtained for cryo-treated buds, against 95% and 0% obtained respectively for non-treated buds. RT-PCR and RT-qPCR analyses did not reveal detectable quantity of YMV in treated plants but did in control plants. Plants from cryo-treated buds showed no mosaic symptoms and produced slightly more tubers, and heavier mini-tubers (20.48±3.11 g) under greenhouse conditions contrary to non-treated plants that showed severe mosaic symptoms with significantly smaller tubers (1.91±0.39 g) (P < 0.05). This is the first report showing the elimination of YMV from infected white yam stock plant by cryotherapy and would be useful for producing clean planting materials.

Effect of processing on proximate composition, anti-nutrient status and amino acid content in three accessions of African locust bean (Parkia biglobosa (jacq.) benth.

Proximate composition, amino acid levels and anti-nutrient factors (polyphenols, phytic acid and oxalate) in the seeds of Parkia biglobosa were determined at three stages: raw, boiled and fermented. The highest anti-nutrient factor present in the raw state was oxalate, while phytic acid was the least. The amino acid of the raw seeds matched favourably to the World Health Organization reference standard. After processing, boiling increased fat, crude fibre and protein, while it reduced moisture, ash and the anti-nutrient content in 64% of the cases examined. Fermentation reduced ash, crude fibre and carbohydrate in all the accessions. It increased the moisture, fat and protein, while reducing the anti-nutrient factors in 78% of the cases. The high levels of protein, fat and amino acids coupled with the low levels of the anti-nutrients in the boiled and fermented seeds make Parkia a good source of nutrients for humans and livestock.