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

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Evaluation of SPAD chlorophyll fluorescence for on-site nitrogen assessment in drip fertigated sweet corn
(2013-04) Kitonga-Mwanza, Lydia L.M.; Swiader, John; Mulwa, Richard M.S.
This study was conducted over two growing seasons to evaluate the potential use of the Minolta SPAD-502 chlorophyll meter for rapid onsite determination of plant N status in a drip-fertigated nitrogen cropping regime of sweet corn. Four N fertilizer rates (0, 84, 168, and 336 kg N ha-1) were applied to two sweet corn cultivars (‘Kandy Plus’ and ‘Sugar Ace’) in a factorial split-plot design. Leaf SPAD and leaf total N concentration were measured at 4 different growth stages (seventh leaf stage (V7), tenth leaf stage V10), silking (R1) and milking (R3) in season one and three sampling stages (V6, V10 and R1) in 2002. In season two, leaf N concentrations and leaf ‘SPAD chlorophyll’ measurements increased early in the season up to silking (R1 growth stage) and declined thereafter. Leaf N concentrations and leaf SPAD readings were positively correlated. Critical SPAD values (readings associated with the lowest N fertilizer rate and providing the highest marketable ear yield) were estimated as 52.8, 52.1 and 59.0 at V7, V10 and R1 in season one; in season two the values were 51.0, 49, and 56.5 receptively. Regressing N rate on yield placed maximum ear yields at 13.8 tons ha-1 with 174.8 kg N ha-1 in season one and 9.7 tons ha-1 with 306.2 kg ha-1 in season two. Increase in leaf SPAD readings at silking reflects a strong sink/source relationship among leaves for absorbed N. The positive relationship between leaf SPAD readings and leaf N status is due to the responsiveness of SPAD-chlorophyll to N fertilizer application. These results indicate that the SPAD meter can be used effectively to assess sweet corn N status early in the season, and at this time it is possible to correct any N deficiencies that might compromise yields.
Occurrence and estimated losses caused by cassava viruses in Migori County, Kenya
(Egerton University, 2016-04) Masinde, Emily Atieno; Ogendo, Joshua Ondura; Maruthi, Midatharahally N.; Hillocks, Rory; Mulwa, Richard M.S.; Arama, Peter Futi
A farm survey was conducted in Kuria East and Suna West sub-counties to determine the incidence, severity and estimated losses of cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) on cassava crops in farmers’ fields. The results showed that cassava is the second most important staple crop after maize in Migori County. CMD incidence ranged from 0.0 to 56.7%) in Kuria East and 10.0 to 55.0% in Suna West. CBSD incidences were much higher at 5.0 to 74.0% in Kuria East and 10.0 to 77.5% in Suna West. Both CMD and CBSD had an effect on yield reduction and total root loss ranged from 10.7 to 47.2% in Kuria East and 11.5 to 33.2 in Suna West. The percent mean total root loss in Kuria East was 25.9%; equivalent to 1299.6 US dollars/ha while in Suna East was 24.7%; equivalent to 1259.5 US dollars/ha. The best performing variety with regards to low CBSD and CMD incidence, low root losses and high yield were TMS 30572 and MH95/0183. The findings of this study are expected to provide impetus for the development and promotion of new high yielding, locally adapted and resistant cassava varieties.
Plant Regeneration via Somatic Embryogenesis from Leaf and Floral Explants of ‘Chancellor’ Wine Grape
(Egerton University, 2006) Mulwa, Richard M.S.; Norton, Margaret M.A.; Skirvin, Robert M.
Abundant embryogenic callus was obtained from leaf and floral explants of ʺChancellorʺ grape by continuous culture for 12 weeks on Nitsch and Nitsch basal medium supplemented with 9 μM 2, 4‐D + 17 μM IASP + either 1 μM BA or 1 μM TDZ (ECIM) in darkness. They were successfully maintained by a five to six week subculture interval on NN medium containing 2 μM 2, 4‐D + 0.2 μM TDZ + 4 μM IASP (LTMM). Near synchronous embryo developed from embryogenic callus on medium containing 10 μM IASP + 8 μM NOA + 1 μM TDZ + 1 μM ABA + 2.5 g/l AC (EDMM). Individually separated somatic embryos were germinated on both NN and half strength of MS containing 0.5 μM BA + 0.025 μM NAA, respectively; normal plantlet conversion from embryos was low (35%). Whole fruiting plants were obtained. Aberrant embryo development was characterized by failure to form functional shoot meristems following the initial cotyledon expansion during germination. These observations indicate that the embryo conversion stage of the regeneration is difficult and remains a limiting factor requiring more empirical experimentation for improvement in grape tissue culture.