Browsing by Author "Mulwa, Richard M. S."

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Assessment of clonal stability of in vitro regenerated shoots of Macadamia tetraphylla by RAPD analysis
(Egerton University, 2007) Mulwa, Richard M. S.; Bhalla, Prem L.
Macadamia nuts constitute an important part of the world nut industry and are highly valued for their health- promoting properties. Macadamia is an open-pollinated crop that takes 8–12 years to bear fruit when multiplied via seeds. The yield and nut quality in seedling plantations are often highly variable, and grafting is currently the most common method for producing nursery trees with reduced variability. We have previously reported on the tissue-culture propagation of macadamia, and in the present study we assessed the clonal integrity of the regenerated shoots. The RAPD proﬁles of 3 macadamia stock plants and 10 in vitro regenerated lines from each stock plant were analysed to assess the clonal integrity of the shoots regenerated in vitro for micropropagation purposes. The extent of genetic variation between the stock plants and 9 randomly selected seedlings was also assessed. There was no difference in clonal identity between the stock plants and their micropropagated progeny, indicating that clonal micropropagation was possible using enhanced axillary proliferation in macadamia. In contrast, there was a large genetic variation among the seedlings and between the seedlings and stock plants, with genetic distance estimates ranging from 0.121 to 0.637 among seedlings, indicating rampant out-crossing of the macadamia plant.
Development and Characterization of Wheat Germplasm with Combined Resistance to Russian Wheat Aphid and Stem Rust (Race “Ug99”) in Kenya
(Scientific Research, 2013-04) Amulaka, Fredrick O.; Maling’a, Joyce N.; Cakir, Mehmet; Mulwa, Richard M. S.
Wheat is the second most important cereal in Kenya. However, production is severely constrained by both abiotic and biotic stresses. Of the biotic stresses a devastating pest (Russian wheat aphid (RWA)) and a serious disease (stem rust race TTKS (“Ug99”)) are currently the biggest problem for wheat producers in Kenya. Severe infestations by RWA may result in yield losses of up to 90% while “Ug99” infected fields may suffer 100% crop loss. The two pests com- bined are seriously affecting wheat farmers’ incomes because of the heavy reliance on pesticides that increase the cost of production. This study attempted to develop and characterize wheat lines that are resistant to both RWA and “Ug99” by pyramiding two major resistance genes. Three wheat varieties: “Kwale”, a Kenyan high yielding variety but suscep- tible to both RWA and “Ug99”; “Cook”, an Australian variety carrying stem rust resistance gene Sr36 conferring im- munity to “Ug99”; and “KRWA9”, a Kenyan line with resistance to RWA but of poor agronomic attributes were used. A double cross F1 (DC F1) was obtained by crossing the F1 of “Kwale × Cook” and the F1 of “Kwale × KRWA9”. The DC F1 population was subjected to sequential screening for both RWA and “Ug99” resistance. Surviving DC F1 proge- nies were left to self pollinate to obtain the F2 of the double cross (DC F2). The DC F2 progenies were sequentially screened against RWA and “Ug99” to yield a population that was resistant to both RWA and “Ug99”. Genotyping of the DC F2:3 families were conducted to select homozygous resistant plants. Data indicated that the RWA and “Ug99” resistance genes were successfully pyramided. Though races with virulence for Sr36 have been reported, the gene pro- vides immunity to race “Ug99” and can still be effectively used as a component for “Ug99” resistance breeding together with other Sr genes.
In vitro plant regeneration from immature cotyledon explants of macadamia (Macadamia tetraphylla L. Johnson)
(Egerton University, 2006-07) Mulwa, Richard M. S.; Bhalla, Prem L.
The macadamia tree, an Australian native, is highly valued for its nuts. Macadamia improvement pro- grams so far have relied on conventional breeding and selec- tion. The production of improved cultivars required to meet future demands could be accelerated by the application of modern biotechnological techniques, but this requires an efficient and reproducible regeneration system that has not yet been established for macadamia. We report here shoot regeneration from immature cotyledon explants of macadamia. Adventitious buds were induced on the cotyle- don explants from fruits collected at 140 and 190 days af- ter full bloom (DAFB) on MS medium supplemented with either 10 or 15 µM TDZ. The addition of 2% coconut milk (CM) to 10 µM TDZ containing media resulted in enhanced adventitious bud induction from 190 DAFB ex- plants. Further shoot development from the induced buds was depressed in media containing TDZ + CM; the addi- tion of 0.001 µM IAA to this combination doubled shoot development, from 1.9–3.9 shoots per explant. The trans- fer of bud clumps to media supplemented with 8.8 µM BA alone or in combination with either 0.14 µM GA3 or 0.001 µM IAA significantly increased shoot production from the previously induced explants by 1.5–2 times of that observed in TDZ + CM medium.