Influence of Inoculum Sources of Pyrenochaeta terrestris on Pink Root Disease Development, Growth and Bulb Yield of Onion

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Date
2015-06-15
Authors
Adam Mirghani Dafaallah Kafi, Kafi
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Publisher
uofk
Abstract
This study was carried out during the period January 2007 to May 2008. Its main objectives were to isolate and identify the causal organism of pink root disease of onion in Zalingei area and to evaluate the influence of the inoculum sources (infected onion transplants versus infested soil) on disease development, growth and bulb yield of onion. The isolated causal organism of Zalingei onion pink root disease was identified as Pyrenochaeta terrestris (Hansen) Gorenz, Walker and Larson, and was designated as Zalinge isolate. It could be grouped under the sterile type since it failed to produce pycnidia under both dark and florescent light. Both sources of inoculum (transplants and soil) resulted in 100% infection and significantly reduced the root development, leaf growth and bulb weight of cv.‘ Kamlin yellow’ when assessed two months after transplanting and at maturity. The impact of transplants’ inoculum on disease severity and plant growth was significantly greater than that of the soil inoculum. The influence was greatest when both sources of inoculum were combined together. The results demonstrated that root infection was absent in the control (healthy transplants grown in non-infested soil), severe in infected transplants grown in non-infested soil (~66.3% and ~ 75% assessed at two months after transplanting and at maturity, respectively) and more severe when both sources of inoculum were present (~87% and ~91% assessed at two months after transplanting and at maturity, respectively). The disease severity in healthy transplants grown in infested soil was significantly lower than that in infected transplants grown in non-infested soil (~17.5% and~ 37% at the two harvest periods, respectively). The bulb weight produced by the healthy transplants was significantly higher (~2 and ~3.5 times as much) than that of the infected ones assessed at two months after transplanting and at maturity, respectively. The bulb weight of onion plants raised in non-infested soil (~20g and ~ 109g) was significantly higher than that raised in contaminated soil (~14g and ~61g) assessed at the harvest periods mentioned above. Based on these results, healthy onion transplants could be included as a major component of pink root disease management program since its performance was obviously superb in non-infested soil and second to the best if planted in contaminated soils. These findings have practical significance and can easily be applied in the field by farmers irrespective of their economic and financial status or educational background. Healthy transplants can be produced even in contaminated lands if certain measures are taken and adopted in a small area (i.e. a nursery). These findings were discussed, few perspectives emerging from the results were pointed out and the future prospectives were suggested
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Influence of Inoculum Sources of Pyrenochaeta terrestris on Pink Root Disease Development, Growth and Bulb Yield of Onion
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