Spelling suggestions: "subject:"downy milder diseases"" "subject:"owny milder diseases""
11 |
Response to selection for downy mildew (Peronosclerospora sorghi) and maize streak virus resistance in three quality protein maize populations in Mozambique /Mariote, David. January 2007 (has links)
Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2007. / Submitted to the African Centre for Crop Improvement. Full text also available online. Scroll down for electronic link.
|
12 |
Investigation of heterotic patterns and genetic analysis of Downy mildew resistance in Mozambican lowland maize (Zea mays L.) germplasm.Fato, Pedro. January 2010 (has links)
In Southern Africa and Mozambique, tropical lowland accounts for 22% and 65%,
respectively, of area under maize production, but grain yield is compromised by downy
mildew disease (DM, which is caused by Peronosclerospora sorghi (Weston and Uppal)
Shaw), and lack of appropriate varieties, especially hybrids. Among other factors,
productivity can be enhanced by deploying DM resistant hybrids, which are higher yielding
than open pollinated varieties. Development of a viable hybrid-breeding programme
requires knowledge of genetic effects governing yield and DM resistance in inbreds, and
effective germplasm management requires heterotic groups and heterotic patterns to be
established. In addition, knowledge of farmer-preferred traits is required. Currently, such
information is not available to the hybrid-breeding programme in Mozambique. The
objectives of this study were, therefore; i) to identify farmers’ preferred variety traits and
major production constraints, ii) to determine combining ability effects of inbred maize S4
lines for grain yield and DM resistance, iii) to determine heterotic groups and heterotic
patterns among the elite inbred maize lines, and iv) to investigate gene effects governing
resistance to DM in breeding source inbred maize lines from the breeding programme in
Mozambique.
During 2007/08, 142 households were involved in a survey conducted in three
districts representing two maize agro-ecological zones in Mozambique. Formal surveys and
informal farmer-participatory methods were employed and data subjected to analysis in the
SPSS computer programme. Results indicated that there was a low utilization of improved
varieties, especially hybrids, with grain yield estimated at 0.7 t ha-1. Farmers were aware of
the major production constraints and could discriminate constraints according to their
importance for their respective communities. For the lowland environment, farmers
identified downy mildew, drought, and cutworm and stem borer damage as the main
constraints. In contrast, for the high altitude environments, they ranked ear rot, seed and
fertilizer availability, turcicum leaf blight, grey leaf spot diseases and low soil fertility among
the major constraints limiting productivity. The most important variety selection criteria were
grain yield, short growth cycle, white and flint grain with stress tolerance to drought, low soil
fertility, diseases, and grain weevils. These afore mentioned traits, would be priority for the
breeding programmes for the lowland and mid altitude environments in Mozambique.
To determine combining ability for downy mildew resistance, heterotic groups and
heterotic patterns, two testers (open-pollinated varieties) ZM523 (Z) and Suwan-1 (S), were
crossed with 18 lines to generate 36 top crosses for evaluation. Crosses were evaluated at
two sites under DM. Preponderance of GCA effects indicated that additive gene effects were
more important than non-additive gene effects in governing both grain yield and downy
mildew resistance in the new maize lines. Based on specific combining ability (SCA) data,
lines for yield were classified into two heterotic groups, S and Z; whereas based on
heterosis data, lines were fitted into three heterotic groups (S, Z and SZ).
Further heterotic patterns and gene action for yield were determined by subjecting
nine inbred lines and the two testers, S and Z, to an 11 x 11 diallel-mating scheme. The
diallel crosses, three hybrid checks and the two testers were evaluated in six environments
in Mozambique. Results revealed that non-additive gene effects were predominant for yield
components. In addition, high levels of heterosis for yield was observed and three heterotic
groups identified (Z, S and S/Z), and five exceptional heterotic patterns among the inbred
elite maize lines were observed. Topcrosses with yield levels comparable to single cross
hybrids were also identified, and these would be advanced in the testing programme with
potential for deployment as alternative cheaper and sustainable technology to conventional
hybrids for the poor farming communities in Mozambique.
To determine gene effects for downy mildew resistance in potential breeding lines,
two maize populations were derived from crosses between downy mildew susceptible line
LP67, and resistant lines DRAC and Suwan-L1. To generate F2 and backcross progenies
(BCP1 and BCP2), F1 progenies were self-pollinated and simultaneously crossed to both
inbred parents (P1 and P2). All the six generations (P1, P2, F1, F2, BCP1, and BCP2) of
the populations were evaluated at two sites under downy mildew infection. A generation
mean analysis was performed in SAS. It was revealed that downy mildew resistance was
influenced by genes with additive and dominance effects, plus different types of epistatic
effects such as additive x additive, and dominance x dominance. Overall results indicated
that genes with predominantly non-additive effects controlled resistance in DRAC, whereas
resistance in Suwan-L1 was largely influenced by additive gene effects. These findings
have serious implications on the effective use of these downy mildew resistance sources in
breeding programmes that aim to generate varieties with downy mildew resistance.
Overall, results suggested that inbreeding and selection within heterotic groups,
followed by hybridization between inbreds within and across heterotic groups would be
effective to generate new hybrids. The breeding programme will consider development of
conventional hybrids, such as single crosses and three way crosses, and top crosses.
Implications of the findings of the study and recommendations are discussed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
|
13 |
Marker-assisted selection for maize streak virus resistance and concomitant conventional selection for Downy Mildew resistance in a maize population.Mafu, Nothando Fowiza. January 2013 (has links)
Maize streak virus (MSV) disease, transmitted by leafhoppers (Cicadulina mbila, Naude), and maize downy mildew (DM) disease caused by Peronosclerospora sorghi (Weston and Uppal) Shaw, are major contributing factors to low maize yields in Africa. These two diseases threaten maize production in Mozambique, thus the importance of breeding Mozambican maize varieties that carry resistance to these diseases. Marker-assisted selection (MAS) was employed to pyramid MSV and DM disease resistant genes into a single genetic background through simultaneous selection. Firstly, it was essential to determine the genetic diversity of MSV disease resistance in 25 elite maize inbred lines to aid in the selection of suitable lines for the introgression of the msv1 gene; and subsequently, to introduce the msv1 resistance gene cluster from two inbred lines, CM505 and CML509, which were identified as the ideal parental lines for the introgression of MSV disease resistance into a locally adapted Mozambican inbred line LP23 that had DM background resistance. Pyramiding the resistance genes by the use of simple sequence repeat (SSR) molecular markers to track the MSV gene cluster was investigated in 118 F3 progeny derived from crosses of CML505 x LP23 and CML509 x LP23. High resolution melt (HRM) analysis using the markers umc2228 and bnlg1811 detected 29 MSV resistant lines. At the International Maize and Wheat Improvement Centre (CIMMYT) in Zimbabwe, MSV disease expression of the 118 F3 progeny lines was assessed under artificial inoculation conditions with viruliferous leafhoppers and the effect of the MSV disease on plant height was measured. Thirty-seven family lines exhibited MSV and DM (DM incidence ≤50) disease resistance. Individual plants from a total of 41 progeny lines, that exhibited MSV disease severity ratings of 2.5 or less in both locations within each of the F3 family lines, were selected based on the presence of the msv1 gene based on SSR data, or field DM disease resistance, and were then advanced to the F4 generation to be fixed for use to improve maize hybrids in Mozambique for MSV resistance. Simultaneous trials were run at Chokwe Research Station in Mozambique for MSV and DM disease assessment, under natural and artificial disease infestation, respectively. Thus the MSV and DM genes were effectively pyramided. Lines with both MSV and DM resistance were advanced to the F4 generation and will be fixed for use to improve maize hybrids in Mozambique for MSV and DM resistance, which will have positive implications on food security in Mozambique. This research discusses the results of combined selection with both artificial inoculation and the three selected SSR markers. It was concluded that a conventional maize breeder can successfully use molecular markers to improve selection intensity and maximise genetic gain. / Thesis (M.Sc.Agric)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
|
14 |
Species of Pythium associated with barley in South Australia / by J.I. BratoloveanuBratoloveanu, J. I. January 1985 (has links)
Bibliography: leaves 140-158 / ix, 158 leaves, [23] leaves of plates : ill., 1 map ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1985) Dept. of Plant Pathology, University of Adelaide
|
15 |
Response to selection for downy mildew (Peronosclerospora sorghi) and maize streak virus resistance in three quality protein maize populations in Mozambique.Mariote, David. January 2007 (has links)
Quality protein maize (QPM) has high nutritional value, but production is threatened by downy mildew (DM) and maize streak virus disease (MSVD) among other constraints. There are few studies of DM and MSVD resistance in QPM cultivars. The objective of this study was to improve resistance to DM and MSVD in three QPM populations. This was realized through ascertaining farmers’ key production constraints and special preferences for cultivars; determining the utility of recurrent selection method for improvement of three QPM populations (SussumaS2, ZM521Q and Pop62SRQ); and determining grain yield potential. The study was conducted in Mozambique for DM and in Zimbabwe for MSV, during 2003 to 2006. Surveys were conducted in Manica and Angonia districts in Mozambique to ascertain farmers’ perceptions and preferences for maize varieties, especially QPM. Participatory rural appraisal tools that included semi-structured questionnaires and focus group discussions were used to collect data. Results showed that farmers predominantly grew open pollinated varieties and fewer normal maize hybrids (non-QPM), and grain yield was estimated to be very low (0.2 to 0.6 t ha-1). Results showed that drought and insect pests were the dominant constraints to maize productivity in Mozambique, while diseases were ranked third. Downy mildew disease and MSVD were considered to be the most important diseases reducing maize productivity. Farmers also showed high preference for high yielding and early maturity cultivars in all areas. Predominantly, farmers were still using their local landraces because of sweet taste, particularly for home consumption and flint grain for storage. Farmers’ access to improved cultivars was limited due to high seed prices on the local market. Research priorities as perceived by the farmers included breeding for resistance to drought, grain weevils and diseases and sweetness. Generally, farmers showed little knowledge of QPM varieties and the importance of this trait, but they observed that the few QPM varieties they knew had some weaknesses such as poor storability and susceptibility to DM and MSVD which required improvement. These results should be considered in breeding new cultivars, both normal and QPM. To improve DM and MSV disease resistance in QPM varieties, S1 recurrent selection was conducted in three QPM populations, Sussuma, ZM521Q and Pop62SRQ at Umbeluzi Research Station in Mozambique and at CIMMYT-Harare Research Quality protein maize (QPM) has high nutritional value, but production is threatened by downy mildew (DM) and maize streak virus disease (MSVD) among other constraints. There are few studies of DM and MSVD resistance in QPM cultivars. The objective of this study was to improve resistance to DM and MSVD in three QPM populations. This was realized through ascertaining farmers’ key production constraints and special preferences for cultivars; determining the utility of recurrent selection method for improvement of three QPM populations (SussumaS2, ZM521Q and Pop62SRQ); and determining grain yield potential. The study was conducted in Mozambique for DM and in Zimbabwe for MSV, during 2003 to 2006. Surveys were conducted in Manica and Angonia districts in Mozambique to ascertain farmers’ perceptions and preferences for maize varieties, especially QPM. Participatory rural appraisal tools that included semi-structured questionnaires and focus group discussions were used to collect data. Results showed that farmers predominantly grew open pollinated varieties and fewer normal maize hybrids (non-QPM), and grain yield was estimated to be very low (0.2 to 0.6 t ha-1). Results showed that drought and insect pests were the dominant constraints to maize productivity in Mozambique, while diseases were ranked third. Downy mildew disease and MSVD were considered to be the most important diseases reducing maize productivity. Farmers also showed high preference for high yielding and early maturity cultivars in all areas. Predominantly, farmers were still using their local landraces because of sweet taste, particularly for home consumption and flint grain for storage. Farmers’ access to improved cultivars was limited due to high seed prices on the local market. Research priorities as perceived by the farmers included breeding for resistance to drought, grain weevils and diseases and sweetness. Generally, farmers showed little knowledge of QPM varieties and the importance of this trait, but they observed that the few QPM varieties they knew had some weaknesses such as poor storability and susceptibility to DM and MSVD which required improvement. These results should be considered in breeding new cultivars, both normal and QPM. To improve DM and MSV disease resistance in QPM varieties, S1 recurrent selection was conducted in three QPM populations, Sussuma, ZM521Q and Pop62SRQ at Umbeluzi Research Station in Mozambique and at CIMMYT-Harare Research. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.
|
Page generated in 0.0801 seconds