Crop Protection & Environmental Biology
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Item Relative efficiency of positive selection and tissue culture for generating pathogen-free planting materials of yam (dioscorea spp.)(2017) Balogun, M.; Maroya, N.; Augusto, J.; Ajayi, A.; Kumar, L.; Aighewi, B.; Asiedu, R.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 tis¬sue 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 deter¬mined 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.Item A somatic embryogenesis-based system for the production of fluted pumpkin (telfairia occidentalis hook F.) planting materials(The Society for In Vitro Biology, 2015) Awosika, D. O.; Uchendu, E.; Balogun, M. O.; Adetimirin, V. O.Fluted pumpkin (Telfairia occidentalis Hook. f.) is traditionally propagated by seeds, which have low viability after pod harvest, low percentage germination, and poor root development and often germinate during storage. The competition between use of seeds for consumption and propagation causes scarcity of propagules, necessitating development of more efficient propagation systems. Efficient protocols were developed for the induction of somatic embryos (SEs) and conversion into plantlets using cotyledons from mature zygotic embryos. This study evaluated the effects of 2,4- dichlorophenoxyacetic acid (2,4-D) and kinetin (25 combinations) on the induction of SEs, and of indole-3-acetic acid (IAA), 2,4-D, and kinetin (7 combinations) on conversion of SEs into plantlets. Significantly more SEs (381.7; p<0.01) were obtained on medium with 0.5 mg l−1 2,4-D and 0.1 mg l−1 kinetin than from the other 24 treatments after 4 wk of cotyledon culture. All SEs were obtained through an intermediary callus. For the production of SE-derived plantlets, treatments with 0.01 mg l−1 IAA and 0.02 mg l−1 kinetin resulted in significantly more shoots and roots than other treatments (p<0.001 for each) and gave 100% conversion of SEs to plantlets. The mean numbers of roots and shoots on this treatment were 3.7 and 1.3, respectively, and the mean shoot length was 2.2 cm. The plantlets had broad leaves and good vigor, similar to the parent cultivar. Nearly all plantlets (98–100%) survived acclimatization. The production of SEs from cotyledons and the high rate of conversion into quality plants will allow development of a mass production system for Telfairia planting material to meet the increasing demand for this crop.Item A somatic embryogenesis-based system for the production of fluted pumpkin (telfairia occidentalis hook F.) planting materials(The Society for In Vitro Biology, 2015) Awosika, D. O.; Uchendu, E.; Balogun, M. O.; Adetimirin, V. O.Fluted pumpkin (Telfairia occidentalis Hook. f.) is traditionally propagated by seeds, which have low viability after pod harvest, low percentage germination, and poor root development and often germinate during storage. The competition between use of seeds for consumption and propagation causes scarcity of propagules, necessitating development of more efficient propagation systems. Efficient protocols were developed for the induction of somatic embryos (SEs) and conversion into plantlets using cotyledons from mature zygotic embryos. This study evaluated the effects of 2,4- dichlorophenoxyacetic acid (2,4-D) and kinetin (25 combinations) on the induction of SEs, and of indole-3-acetic acid (IAA), 2,4-D, and kinetin (7 combinations) on conversion of SEs into plantlets. Significantly more SEs (381.7; p<0.01) were obtained on medium with 0.5 mg l−1 2,4-D and 0.1 mg l−1 kinetin than from the other 24 treatments after 4 wk of cotyledon culture. All SEs were obtained through an intermediary callus. For the production of SE-derived plantlets, treatments with 0.01 mg l−1 IAA and 0.02 mg l−1 kinetin resulted in significantly more shoots and roots than other treatments (p<0.001 for each) and gave 100% conversion of SEs to plantlets. The mean numbers of roots and shoots on this treatment were 3.7 and 1.3, respectively, and the mean shoot length was 2.2 cm. The plantlets had broad leaves and good vigor, similar to the parent cultivar. Nearly all plantlets (98–100%) survived acclimatization. The production of SEs from cotyledons and the high rate of conversion into quality plants will allow development of a mass production system for Telfairia planting material to meet the increasing demand for this crop.Item Relative effects of uniconazole-p and other growth regulators on micropropagation ratio of yam (dioscorea spp.) plantlets at different growth phases(Indian Society for Root Crops, 2014) Balogun, M. O.; Ng, S. Y.; Fawole, I.; Shiwachi, H.; Kikuno, H.Scarcity of planting materials, pest and diseases are major constraints to yam production. The tissue culture techniques, meristem culture combined with heat therapy has been used to produce high-yielding virus-tested plantlets of root crops, which are later multiplied through micropropagation. This procedure, however has low regedaration and multiplication rates in yam. We investigated effects of different plant growth regulators on rate of growth of yam plantlets when applied at different growth phases. Three concentrations each of uniconazole-p (UP), gibberellic acid (GA3), jasmonic acid(JA) and naphthalene acetic (NAA) acids were applied at single node and primary nodal complex (PNC) formation phases in a split-plot design using two genotypes each of white and water yam. Number of nodes per plantlet was recorded after 16 weeks. Results showed that number of new nodes varied significantly with genotype by growth phase interaction and the main effect of PGRs. After 16 weeks, the control, 1.7 μM UP and 0.03 μM JA showed highest means of 7, 9 and 8 nodes per plantlet respectively compared to 2-3 nodes in the GA treatments. We demonstrated that 4900, 8100 and 6400 plantlets could be obtained in one year using 100 nodes by sub-culturing them four times. Addition of PGRs at PNC doubled the number of nodes per plantlet. However the effect of stage of treatment varied with genotypes. The GA and its inhibitor, UP influenced the multiplication rate of yam.