Cassava mosaic disease resistant clones’ growth and yield are prone to early drought stress

Open Access JournalThis study was conducted to evaluate the growth and yield stability of cassava mosaic disease (CMD) resistant breeding populations clones against early drought. Field trials were planted using 200 CMD resistant clones and 7 local landraces in a randomised complete block design with 3 replicates at the International Institute of Tropical Agriculture (IITA) station, Sendusu in Namulonge (Central Uganda) during the second rains of 2006 (2006B) and the first rains of 2007 (2007A). The 2007A crop suffered from drought stress in the first 4 months after planting (MAP). Data were taken on the leaf lobe length and width at 6 MAP and plant height at 12 MAP. Harvest was done at 12 MAP during which the number of storage roots per plant and storage root yield were recorded. Data were analysed using the Mann-Whitney U test to compare crop performance between the 2 seasons. The 2006B crop had significantly (P<0.01) longer leaf lobes, taller plant heights, higher number of storage roots per plant and higher storage root yield than the 2007A crop. There was no significant difference in the leaf lobe width. In this experiment, it was observed that the CMD resistant breeding clones were susceptible to early drought and thus it was recommended that selections should be done for higher water use efficiency

Efeito da duração da fragmentação e concentração do micélio na virulência de Mycosphaerella fijiensis em bananeirat

Mycelia from 3 isolates of Mycosphaerella fijiensis (Mak 01, Mak 02 and Kaw 10) were fragmented for 3 and 1 minutes, and tested at 5 mg mL-1, 10 mg mL-1 and 15 mg mL-1 for virulence in the screen house. Disease severity was found to depend on the level of fragmentation and concentration. Inoculation of Gros Michel plantlets with mycelia fragmented for 3 minutes resulted in significantly higher levels of disease severity (AUDPC) than fragmentation for 1 minute for all the isolates. For both times of fragmentation, AUDPC increased with concentration. The highest and lowest AUDPCs for both times of fragmentation were achieved with concentrations of 15 and 5 mg mL-1, respectively. Overall, all the three isolates demonstrated high levels of virulence, with Mak 01 causing the highest severity (AUDPC - 98.5) when compared to Mak 02 (AUDPC - 93.5) and Kaw 10 (AUDPC - 92.2) for 3-minute fragmentation and concentration of 15 mg mL-1. Collectively, our data demonstrate that a potent inoculum of Mycosphaerella fijiensis for in vitro studies can be reliably prepared by fragmenting weighed mycelia in a blender.Los micelios de 3 aislamientos de Mycosphaerella fijiensis (Mak 01, Mak 02 y Kaw 10) se trituraron durante 3 y 1 minutos y se probaron a 5 mg mL-1, 10 mg mL-1 y 15 mg mL-1 para la virulencia en el hogar. pantalla. Se encontró que la gravedad de la enfermedad depende del nivel de fragmentación y concentración. La inoculación de plántulas de Gros Michel con micelio triturado durante 3 minutos resultó en niveles significativamente más altos de gravedad de la enfermedad (AUDPC) que la trituración durante 1 minuto para todos los aislamientos. Para ambos tiempos de fragmentación, el AUDPC aumentó con la concentración. Las AUDPC más altas y más bajas para ambos tiempos de fragmentación se obtuvieron con concentraciones de 15 y 5 mg mL-1, respectivamente. En general, los tres aislamientos demostraron altos niveles de virulencia, con Mak 01 causando la mayor gravedad (AUDPC - 98,5) en comparación con Mak 02 (AUDPC - 93,5) y Kaw 10 (AUDPC - 92,2) para fragmentación de 3 minutos y concentración de 15 mg ml-1. Colectivamente, nuestros datos demuestran que un potente inóculo de Mycosphaerella fijiensis para estudios in vitro se puede preparar de manera confiable triturando micelios pesados ​​en una licuadora.Micélios de 3 isolados de Mycosphaerella fijiensis (Mak 01, Mak 02 e Kaw 10) foram fragmentados por 3 e 1 minutos, e testados em 5 mg mL-1, 10 mg mL-1 e 15 mg mL-1 para virulência na casa de tela. Verificou-se que a gravidade da doença depende do nível de fragmentação e concentração. A inoculação de plântulas de Gros Michel com micélio fragmentado por 3 minutos resultou em níveis significativamente mais altos de severidade da doença (AUDPC) do que a fragmentação por 1 minuto para todos os isolados. Para ambos os tempos de fragmentação, AUDPC aumentou com a concentração. As maiores e menores AUDPCs para ambos os tempos de fragmentação foram obtidas com concentrações de 15 e 5 mg mL-1, respectivamente. No geral, todos os três isolados demonstraram altos níveis de virulência, com Mak 01 causando a maior gravidade (AUDPC - 98,5) quando comparado com Mak 02 (AUDPC - 93,5) e Kaw 10 (AUDPC - 92,2) para fragmentação de 3 minutos e concentração de 15 mg mL-1. Coletivamente, nossos dados demonstram que um inóculo potente de Mycosphaerella fijiensis para estudos in vitro pode ser preparado de forma confiável fragmentando micélios pesados em um liquidificador

Combining Ability Analysis of Dry Matter Content, Reducing Sugars and Yield of Potato (Solanum tuberosum L.) Genotypes in Uganda

Potato (Solanum tuberosum L.) in Uganda is a major food and cash crop mainly grown in the highland regions by small-scale farmers. The increasing importance of potato as a processed product requires new varieties possessing quality processing attributes with acceptable yield. The objectives of this study were to estimate the combining ability effects for dry matter content, reducing sugars, and yield related traits in potato. Nineteen F1 families generated from eight parents using a half diallel mating design were evaluated for dry matter content, reducing sugars, average weight per tuber and total tuber yield at Kachwekano research station. Additive genetic effects were predominant for dry matter content while non-additive effects for the other traits. The GCA/SCA ratios were 0.58, 0.28, 0.17 and 0.44 for dry matter content, reducing sugars, average weight per tuber and total tuber yield respectively. Broad sense heritability estimates were 50.6% for dry matter content, 77.8% for reducing sugars, 90.3% for average weight per tuber and 29.5% for total tuber yield. Parents NAROPOT 3 and 395096.2 had desirable GCA effects for both dry matter content and reducing sugars. Families of nkrk19.17 x Rutuku had desirable SCA effects for dry matter content while Rutuku x 393077.54 and nkrk19.17 x 392657.8 had desirable SCA effects for reducing sugars. Additive genetic effects for dry matter content imply that, genetic gains can be achieved through different selection methods and trait transferred to the respective progenies. The selected parents and families will be subjected to further clonal evaluation and selection

Pseudocercospora fijiensis mycelia-based infection system enhances investigational efficacy of P. fijiensis-banana pathosystem

Screening procedures for black Sigatoka have limitations. Thus, there is need for alternative screening procedure. A robust controlled-environment methodology for testing reaction of banana genotypes to Pseudocercospora fijiensis is, thus, still required. The objective of this study was, therefore, to assess the effect of P. fijiensis fragmented mycelia-based inoculum on black Sigatoka development in banana under screen house conditions with the view of developing a procedure for early assessment of resistance. Black Sigatoka severity increased significantly (P &lt; 0.05) over time in all genotypes apart from Kayinja. Significant differences (P &lt; 0.05) in severity were also recorded among the genotypes at 3, 4, 5 and 6 weeks after inoculation. All east African highland banana and plantain genotypes tested exhibited susceptible reaction, characterized by rapid progression of symptoms to necrotic lesions. Kayinja and M9 hybrids exhibited resistant reactions, characterized by small necrotic specks and chlorotic or brown blotches, respectively. The fragmented mycelia-based infection system classified the banana genotypes into resistant and susceptible clones, making it a reliable and efficient infection technique to assess black Sigatoka disease damage. The infection system is recommended for early screening for black Sigatoka resistance

Flowering problems and their possible solution in cassava breeding

Six elite cassava clones were chosen from cassava breeding program at the National Crops Resource Research Institute (NaCRRI) based on their flowering characteristics and seed set. The clones were planted in randomized complete block experimental design with 3 replications. The floral biology of these cassava clones were studied, focusing on morphological traits and developmental timing. Since cassava develops branches in levels, data was sourced from the 1st level of branching through the 4th level of branching. The result indicated that days to branching generally varied among all the genotypes studied, indicating the need to use different planting dates for different genotypes to ensure synchronization of flowering. The time difference among genotypes from branching to visible inflorescence was not larger than one and a half days and this difference did not seem to be a factor for synchronization. The general number of female flowers was low in all genotypes across branching levels. This suggests there is a need to apply techniques that could enhance flowering in cassava. Conversely, the number of male flowers outnumbered the female flowers, suggesting that male flower production may not be a limiting factor to hybrid seed production. The male flower opened 20 to 30 days later after the opening of the female flowers. This calls for delayed planting of the early flowering genotypes when used as female parent. It was recommended that in order to synchronize flowering, the late flowering genotypes have to be planted ahead of the early flowering genotypes. In addition, applying techniques such as growth regulators, red light and finding the most optimal locations for flowering is recommended for further study as a way of enhancing flowering among cassava genotypes

Inheritance of resistance to common bacterial blight in four selected common bean (\u3ci\u3ePhaseolus vulgaris\u3c/i\u3e L.) genotypes

Common bacterial blight (CBB) is the most serious bacterial disease of common bean in Uganda. It causes severe yield losses of up to 62%. Genetic resistance is the most effective option for controlling CBB in smallholder common bean production systems. This study was carried out to determine the inheritance pattern of CBB resistance in leaf and pod of four new resistance sources. The four resistant and four susceptible genotypes were crossed in a half-diallel mating design. F1 individuals were advanced to F2 and evaluated with the parents, in a randomized complete block design replicated twice. Combining ability analysis was performed according to Griffing\u27s (1956) method IV and model 1 using Genstat 12th. General combining ability effects were significant whereas specific combining ability was not suggesting that resistance to CBB in leaf and pod was primarily controlled by additive genes effects. The estimated narrow sense coefficient of genetic determination was moderately high (0.65) for the resistance in leaf and high (0.83) for resistance in pod suggesting that early-generation selection would be effective. Baker’s ratio estimates were relatively high for resistance in leaf (0.79) and pod (0.9) suggesting that hybrids’ performance can be predicted based on the parents’ general combining ability (GCA) effects

Genotype by environment interaction effects on grain yield of highland maize (Zea mays L) hybrids

Maize varieties adapted to highland environments are generally scarce in East and Central Africa (ECA) since most breeding efforts have focused on mid-altitude maize. As a result, farmers in the highlands of Uganda mainly grow varieties that are bred for the mid-altitude zones. Since these maize varieties are not adapted to highland conditions, their productivity in this region rarely exceeds 2 t ha-1. This study was aimed at determining the effect of genotype by environment interactions (GEI) on the grain yield of highland maize hybrids. The study was conducted in three highland locations of Uganda in the maize growing season of March to October 2015. Thirty-six F hybrids and two checks were arranged in a 2 x18 (0, 1) alpha lattice design with two replications. Hybrid by location interaction had highly significant differences (P ≤ 0.001) and explained 46.2% of phenotypic variance. Genotype by environment interactions (GEI), thus, had a strong effect on grain yield. Analyses revealed two maize mega- environments, with AMH701-9/AMH703-22 hybrid emerging the best genotype in Kachwekano and Kalengyere (6.69 t ha-1 and 14.30 t ha-1), and AMH701-9/AMH701-20 hybrid being the best in Buginyanya (14.39 t ha-1). Efforts to breed for high yielding maize cultivars for the highland areas of Uganda should therefore focus more on specific adaptation than broad adaptation