The Response of White Yam (Dioscorea rotundata Poir) Tuber Portions to Positive Selection for Quality Seed Yam Production

Abstract

The production of yams is constrained by high cost and unavailability of clean planting materials, pests and diseases. Vegetative propagation has also caused a build of up diseases, reported to cause up to 80% yield reduction due to scarcity of quality declared seeds. Planting of disease-free material has been found to be effective in reducing disease problems in plants. This study was conducted to produce clean seed yam by reducing yam diseases through positive selection method. In this method, apparently healthy yam plants were identified, tagged (positive selection), assessed for yam mosaic virus incidence and severity using the scale 0 or 1 and 1-5 respectively. The harvested clean tubers from tagged plants were planted the following season so as to determine the rate of response of each genotype and tuber portion to positive selection. At the end of two cycles of positive selection, analysis of variance for percentage number of positive yam plants, YMV incidence, YMV severity and tuber yield shows significant difference (p ≤ 0.05) between positive selection and no selection for both field and screen house plants. It was observed that positively selected plants performed significantly (p ≤ 0.05) better than no selection plants. For field experiment, Number of positively selected plants was highest in positive TDr89/02665 with mean value of 75.00% while no selection Ogoja had the least number of positive plants (17.8%). A yield increase of 1.80 t/ha was recorded due to the application of positive selection method in two cycles. For screen house experiment, result followed a similar trend; however with a reduction in YMV incidence and severity. It is worthy to note that tail portions of yam were lest infected with YMV, hence more healthy plants were selected from the tail portion.

Enhancing productivity of farmer-saved seed yam in Ghana: Positive selection and neem leaf powder factors

“…Apart from reduction in incidence of mosaic disease, yields of seed yam significantly increased in PS compared to FP options. This agrees with findings of Aihebhoria et al (2017) who worked on the response of white yam tuber portions to Positive Selection for quality seed yam production in Nigeria and found out that in addition to reductions in YMV incidence and severity, fresh tuber weight was significantly higher than control plots. In their study, the authors found out that PS fields recorded a tuber yield of 6.03 t ha -1 compared with 4.99 t ha -1 for FP plots.…”

“…3) can be attributed to the accumulation of viruses in farmer saved-seed over multiple cycles of vegetative propagation, the possible exchange of yam materials between farmers and from market sources. This result agrees Aihebhoria et al (2017) that farmer saved seed yam harbor disease pathogens. Galling incidence and index were greater in FP seeds than with PS seeds.…”

Low Soil Nutrient Tolerance and Mineral Fertilizer Response in White Guinea Yam (Dioscorea rotundata) Genotypes

“…The planting materials used in our trial, including the local variety, were visually selected disease-free tubers from disease-free plants. Work done in IITA on a positive selection with seed yam showed a significant decrease in virus incidence and disease severity score while maintaining reasonably good yields (Aihebhoria et al, 2017). However, we did not index the virus status of the planting materials in our trial and acknowledge the sub-optimal yield of local variety could be a confounded effect of the health status of the variety used in the trial.…”

Relative efficiency of positive selection and tissue culture for generating pathogen-free planting materials of yam (Dioscorea spp.)

“…Among plants raised from the same mother tuber, some stands were positive for viruses and others were negative. Aiheiboria (2015) reported that plants raised from the head portions of tuber had the highest mean value for incidence and severity of YMV infection while the tail portions were least infected and discussed that as photosynthates flow down to the tuber, they carry along the virus particles. Thus, virus concentration varied with tuber portion, and by extension, it suggests that the smaller the seed tuber portion, the higher the probability of uniformly virus-free progenies from it.…”