Application of simple sequence repeats (SSRs) markers to study the resistance of locally adapted maize hybrids to damaging maize streak virus disease

Simple sequence repeat markers were used to study S6 recombinant inbred lines originating from a single cross between two inbred lines OSU 23i and EM12-210, for resistance to maize streak virus disease. A total of 115 recombinant inbred lines belonging to three families previously selected using conventional methods were screened using 52 SSR markers contained between Bin 1.04 and 1.05 of maize chromosome 1. Of these, only three markers were chosen on the basis of their polymorphism content for use in the study. This paper discusses the results of combined selection with both artificial inoculation and the three selected SSR markers. The use of artificial inoculation detected 78 resistant lines and 36 susceptible lines. On the other hand, the SSR markers detected 40 resistant lines, and 74 susceptible lines. But a combination of both the artificial inoculation and SSR marker selection reduced the number of resistant lines to 29 and increased the number of susceptible lines to 85. With these findings it was concluded that, a conventional maize breeder requires the use of molecular markers inorder to improve selection intensity and maximize genetic gai

Application of simple sequence repeats (SSRs) markers to study the resistance of locally adapted maize hybrids to damaging maize streak virus disease

Simple sequence repeat markers were used to study S6 recombinant inbred lines originating from a single cross between two inbred lines OSU 23i and EM12-210, for resistance to maize streak virus disease. A total of 115 recombinant inbred lines belonging to three families previously selected using conventional methods were screened using 52 SSR markers contained between Bin 1.04 and 1.05 of maize chromosome 1. Of these, only three markers were chosen on the basis of their polymorphism content for use in the study. This paper discusses the results of combined selection with both artificial inoculation and the three selected SSR markers. The use of artificial inoculation detected 78 resistant lines and 36 susceptible lines. On the other hand, the SSR markers detected 40 resistant lines, and 74 susceptible lines. But a combination of both the artificial inoculation and SSR marker selection reduced the number of resistant lines to 29 and increased the number of susceptible lines to 85. With these findings it was concluded that, a conventional maize breeder requires the use of molecular markers in order to improve selection intensity and maximize genetic gai

The influence of low frequency sea surface temperature modes on delineated decadal rainfall zones in Eastern Africa region

Influence of low frequency global Sea Surface Temperatures (SSTs) modes on decadal rainfall modes over Eastern Africa region is investigated. Fore-knowledge of rainfall distribution at decadal time scale in specific zones is critical for planning purposes. Both rainfall and SST data that covers a period of 1950–2008 were subjected to a ‘low-pass filter’ in order to suppress the high frequency oscillations. VARIMAX-Rotated Principal Component Analysis (RPCA) was employed to delineate the region into decadal rainfall zones while Singular Value Decomposition (SVD) techniques was used to examine potential linkages of these zones to various areas of the tropical global oceans. Ten-year distinct decadal signals, significant at 95% confidence level, are dominant when observed in-situ rainfall time series are subjected to spectral analysis. The presence of variability at El Niño Southern Oscillation (ENSO)-related timescales, combined with influences in the 10–12 year and 16–20 year bands were also prevalent. Nine and seven homogeneous decadal rainfall zones for long rainfall season i.e. March-May (MAM) and the short rainfall season i.e. October-December (OND), respectively, are delineated. The third season of June–August (JJA), which is mainly experienced in western and Coastal sub-regions had eight homogenous zones delineated. The forcing of decadal rainfall in the region is linked to the equatorial central Pacific Ocean, the tropical and South Atlantic Oceans, and the Southwest Indian Ocean. The high variability of these modes highlighted the significant roles of all the global oceans in forcing decadal rainfall variability over the region

The use of simple sequence repeats markers to study genetic diversity in maize genotypes resistant to gray leaf spot disease

Genetic diversity in maize (Zea mays L.) is an important tool for progress in selection for traits of interest. The objective of this study was to screen genotypes for presence of markers linked to plantdefense against fungal diseases, and to study the genetic diversity in gray leaf spot resistant maize genotypes. Forty-one genotypes comprising of collections from Kenya, International Maize and WheatImprovement Centre, the International Institute for Tropical Agriculture and South Africa were identified to be resistant to gray leaf spot in Kenya in 2004. The genotypes were analyzed for variability by usingtwenty-eight microsatellite markers covering the entire maize genome. The results indicated diversity among lines for selected markers. Based on the diversity tree, ten clusters were observed. All genotypes occurred in clusters, except for genotypes EC573- (R12) C8S3-14-1, REGN 99/6, H623 and VHCY. The data indicated that, at least one line in each cluster showed a relationship in a locus with a corresponding parent. Occurrence of related lines also implied that there were common alleles that could have contributed to the gray leaf spot resistance

Sensitivity of Anopheles gambiae population dynamics to meteo-hydrological variability: a mechanistic approach

<p>Abstract</p> <p>Background</p> <p>Mechanistic models play an important role in many biological disciplines, and they can effectively contribute to evaluate the spatial-temporal evolution of mosquito populations, in the light of the increasing knowledge of the crucial driving role on vector dynamics played by meteo-climatic features as well as other physical-biological characteristics of the landscape.</p> <p>Methods</p> <p>In malaria eco-epidemiology landscape components (atmosphere, water bodies, land use) interact with the epidemiological system (interacting populations of vector, human, and parasite). In the background of the eco-epidemiological approach, a mosquito population model is here proposed to evaluate the sensitivity of <it>An. gambiae </it>s.s. population to some peculiar thermal-pluviometric scenarios. The scenarios are obtained perturbing meteorological time series data referred to four Kenyan sites (Nairobi, Nyabondo, Kibwesi, and Malindi) representing four different eco-epidemiological settings.</p> <p>Results</p> <p>Simulations highlight a strong dependence of mosquito population abundance on temperature variation with well-defined site-specific patterns. The upper extreme of thermal perturbation interval (+ 3°C) gives rise to an increase in adult population abundance at Nairobi (+111%) and Nyabondo (+61%), and a decrease at Kibwezi (-2%) and Malindi (-36%). At the lower extreme perturbation (-3°C) is observed a reduction in both immature and adult mosquito population in three sites (Nairobi -74%, Nyabondo -66%, Kibwezi -39%), and an increase in Malindi (+11%). A coherent non-linear pattern of population variation emerges. The maximum rate of variation is +30% population abundance for +1°C of temperature change, but also almost null and negative values are obtained. Mosquitoes are less sensitive to rainfall and both adults and immature populations display a positive quasi-linear response pattern to rainfall variation.</p> <p>Conclusions</p> <p>The non-linear temperature-dependent response is in agreement with the non-linear patterns of temperature-response of the basic bio-demographic processes. This non-linearity makes the hypothesized biological amplification of temperature effects valid only for a limited range of temperatures. As a consequence, no simple extrapolations can be done linking temperature rise with increase in mosquito distribution and abundance, and projections of <it>An. gambiae </it>s.s. populations should be produced only in the light of the local meteo-climatic features as well as other physical and biological characteristics of the landscape.</p

Performance of Three-Way Cross Hybrids for Agronomic Traits and Resistance to Maize Streak Virus Disease in Kenya

Maize Streak virus (MSV) disease is a major disease in many parts of Africa, and is the most important viral pathogen of maize in Kenya. A study was conducted in 2004 to evaluate the agronomic performance and maize streak virus (MSV) resistance of maize ( Zea mays L.) three-way crosses developed in Kenya. Twenty hybrids and one check were grown under normal conditions in a randomized complete block design, in two replications at Embu, 1540 masl; and Muguga, 2093 masl). In a parallel trial in Muguga, hybrids were also evaluated in two replications under artificial inoculation with MSV. The analyses of variance combined across environments showed significant differences (P<0.05) among genotypes for grain yield, days to 50% pollen shed, days to mid-silk and ear height. Genotype x environment interaction was significant (P<0.01) for grain yield and days to mid-silk, indicating some hybrids were more adapted in some environments. Grain yield for MU03-025 (10.04 t ha-1) was significantly better (P<0.05) than the check, H513 (7.53t ha-1). In the disease inoculated experiment, the best hybrids for disease resistance were MU03-012 and MU03-006 (score of 1.75), while H513 had a mean score of >3.0. The highest yielding hybrid under disease inoculation, MU03-026 showed yield gain of 5.2 t ha-1 above that of H513. The results indicate adoption of disease resistant hybrids would result in a higher maize yields in the mid-altitude areas of Kenya

Plant regeneration from immature embryos of Kenyan maize inbred lines and their respective single cross hybrids through somatic embryogenesis

Field grown, self pollinated maize genotypes were planted in KARI (Kiboko and Kabete) research stations between January 2004 and May 2005. Immature maize embryos from twelve parental inbred lines andtheir respective single cross hybrids were evaluated for their ability form callus, somatic embryos and subsequent regeneration into plants. The embryos were excised from surface sterilized kernelsharvested at different physiological stages, namely 10 - 24 days after pollination (DAP). They were used as explants to initiate callus on solid N6 basal media with varying level of 2,4-D (0 - 20 mg L-1) andregenerated on hormone free MS media. Optimal induction of primary callus at 2 mg L-1 averaged 83% and 67 in hybrids and inbred lines respectively. Somatic embryo competence was demonstrated in 6inbreeds and 4 hybrids. However, plant regeneration was only achieved in 4 inbreeds and 3 hybrids. 90% percent of regenerants were normal and fertile. The successful regeneration of some of the inbredlines and/or hybrids provides a basis for development of genetic transformation using Agrobacterium tumefaciens to improve priority traits such as enhanced insects/pest and drought tolerance