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

Abstract

Balogun M., Maroya N., Augusto J., Ajayi A., Kumar L., Aighewi B., Asiedu R. (2017): Relative efficiency of positive selection and tissue culture for generating pathogen-free planting materials of yam (Dioscorea spp.). Czech J. Genet. Plant Breed., 53: 9-16.Yams are staples in West Africa. They are propagated from tubers in an informal seed system. This encourages a build-up of diseases, and necessitates the rapid development of a formal seed system where certified seeds are functional. Although few reports exist on the use of meristem culture to generate pathogen-free yam, the success rate for the most economically important species in the sub-region, Dioscorea rotundata, for the most prevalent viruses is inadequate. To generate pathogen-free yam planting materials, the relative efficiency of tissue culture and positive selection was compared. Twenty-one asymptomatic yam plants were positively selected from 8187 stands of five landraces. Five of these stands were tested virus-negative by multiplex polymerase chain reaction (PCR) for Yam mosaic virus (YMV), Yam mild mosaic virus (YMMV) and Cucumber mosaic virus (CMV), and by PCR for the genus Badnavirus (BV), giving 0.08% success. Single nodes of the positively selected stands were used to establish in vitro plantlets, which were screened onto bacteriological indexing medium. The same was done for meristem-and node-derived plantlets of the improved variety TDr 95/19158. Incidence of endophytes ranged from 18 to 32% in the nodal plantlets while it was 0% in the meristem-derived plantlets. The effect of meristem culture combined with thermotherapy on the virus infection status was determined using virus-tested, one week old in vitro plantlets of eight improved genotypes. These in vitro plantlets were incubated at 36 ± 0.5°C and 16 h photoperiod for 21 days, after which meristems were excised, regenerated into plantlets and re-tested for viruses. Seventy-three percent of the samples were recovered from YMV but the effect on BV was inconsistent. Positive selection can be used as a palliative in generating quality declared seed but meristem culture combined with thermotherapy is more efficient for generating certified seed tubers of yam.

A method for generating virus-free cassava plants to combat viral disease epidemics in Africa

“…Tolerant and resistant plants were cleaned in the first cycle, which took only about 8–10 months. Cleaning of vegetatively-propagated crops like cassava in this study and bananas, potatoes, sweetpotatoes, sugarcane and other crops by others has been done before [21,22,24]. However, cleaning and germplasm exchange at regional level is the first of its kind to our knowledge for any vegetatively-propagated crop and sets an example to follow for other crops for better disease control, improved yields and food securities.…”

“…These protocols have long been used for generating virus-free plants in several other crop plants including the main root and tuber crops of Africa such as cassava, yams and sweetpotatoes. In a recent study, up to 73% of the yam plants were confirmed to be free from Yam mosaic virus following tissue culture and heat therapies, and while the results for other viruses were inconsistent [21]. Such protocols are also adapted by the regulatory bodies in Ethiopia and Tanzania for generating certified seeds of sweetpotatoes [22].…”

Tissue culture and next-generation sequencing: A combined approach for detecting yam (Dioscorea spp.) viruses

“…Studies by Aighewi et al and IITA showed that aeroponics and temporary immersion bioreactor systems (TIBs) produce improved multiplication rates and higher-quality planting material compared with techniques using ware and seed tubers (including the minisett technique) or vine cuttings [39,40]. These in vitro culture techniques can potentially deliver high-quality, clean, clonal plant material and may therefore represent a sustainable solution for the rapid production of pathogen-free planting material [39,41].…”

“…Yam tissue culture is currently used in the exchange of genetic material between countries, and in scientific research, such as rapid increase of planting material for phenotyping to various biotic and abiotic stresses, in the efficient transformation of yam lines, for the production of virus-free yam lines, and other applications. Techniques and applications for the in vitro propagation of members of the genus Dioscorea have been widely researched [38,[41], [42], [43], [44], [45], [46], [47]], and revealed that in vitro propagation and virus indexing for the two most important yam species, D. alata and D. rotundata , still need improvements.…”

Phytosanitary Interventions for Safe Global Germplasm Exchange and the Prevention of Transboundary Pest Spread: The Role of CGIAR Germplasm Health Units

“…The other viruses detected in yam either cause mild mottling or no symptoms at all. Many yam viruses are not regulated, although the IITA uses protocols to generate virus-free in vitro plants for conservation and distribution [ 66 ]. Virus elimination is achieved by selecting asymptomatic plants for thermotherapy and regeneration of in vitro plants from meristem explants.…”