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Use of Polyethylene Glycol (PEG) 8000 for Rapid Screening of Potato (Solanum tuberosum L) Genotypes for Water Stress ToleranceSuharjo, Usman Kris Joko January 2004 (has links) (PDF)
No description available.
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Evaluation of selected sweetpotato (Ipomoea batatas) accessions for drought toleranceOmotobora, Babajide Olusegun 06 1900 (has links)
Sweetpotato (Ipomoea batatas) is a major staple food in Africa and the rest of the world where they are discovered to be a good source of carbohydrates, vitamin A, vitamin C and protein. The maximum production potential of the crop is being hampered by severe drought which ravages most parts of Africa.
The main aim of this project therefore is to screen collected accessions of sweetpotatofor drought tolerance in a quick screening method with a view to identify cultivars that can perform well under water stress conditions.
Fifty selected sweetpotato accessions consisting of cultivars and breeding lines collected from the ARC-VOPI gene bank were planted for drought screening in the glass house for 6 weeks during which water was withheld to induce stress. Observations were made on number of dead plants and days to wilting point, the results were analyzed and 12 best performing cultivars were selected for field trials.
The field trial was carried out in Lwamondo, Thohoyandou for 6months under rain-fed conditions. The experiment was conducted in a complete randomized block design with 6 replicates.Yield data and growth parameters were collected every 8 weeks during the trial period and the data collected was analyzed using ANOVA. The best performing cultivars were Zapallo, Tacna, Ejumula, 2004-9-2 and Ndou. They were therefore recommended for further evaluation in other drought prone areas of the country. / Agriculture and Animal Health / M. Sc. (Agriculture)
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Breeding sweetpotato (Ipomoea batatas [L.] Lam.) for drought tolerance in Kenya.Kivuva, Benjamin Musembi. January 2013 (has links)
Sweetpotato (Ipomoea batatas (L.) Lam.) is an important food crop in East Africa including
Kenya. The crop incurs high yield losses in production due to biotic (insect pests and diseases)
and abiotic (drought, and heat) constraints. Among abiotic constraints, drought is the most
important. Prolonged periods of drought in arid and semi-arid areas of Kenya have led to
reduced quantity and quality of sweetpotato storage roots and in severe cases caused total crop
failure. The objectives of this study were to: 1) determine sweetpotato production system
constraints and farmers’ coping strategies; 2) evaluate sweetpotato clones for yield performance
and drought tolerance; 3) analyse genotype x environment interaction and stability for storage
root yield of selected clones, 4) determine mechanisms of drought tolerance in sweetpotato, and
5) determine combining ability and heterosis for yield and drought tolerance traits under
managed drought stress conditions.
To determine the production constraints and farmers’ coping strategies, a survey was
conducted in central, eastern and western Kenya. Out of 345 farmers interviewed, 60% were
women, and 40% men. Farm sizes ranged from 0.4-0.8 ha, with 90% of sweetpotato cultivated
on 0.2 ha or less. The main sweetpotato varieties were Vitaa, Kabonde and Bungoma and the
majority of farmer’s used their own conserved planting material which was conserved by leaving
them in the field after harvest. About 35% of the farmers identified weevils as the major pest,
and sweetpotato virus disease (SPVD) as the major disease, while 28% of the farmers identified
drought as a major constraint. The farmers used clean seed, high yielding varieties, high
planting density, and manure application as the main strategies to cope with sweetpotato
production constraints.
Eighty four sweetpotato clones were evaluated under managed drought stress environments at
KARI-Kiboko and KARI-Thika. Drought reduced the fresh weight of storage roots (FSR)
(72.5%), fresh biomass weight (FB) (74.0%), marketable fresh storage root (MFSR) (80.7%),
number of storage roots (NSR) (24.5%), days to permanent wilting point (DPWP) (0.3%), but
seemed to increase percent root dry matter (% RDM) (-4.7%), harvest index (HI) (-2.6%), and
chlorophyll content (CC) (-2.7%). Across the environments, genotypes 194555.7 (1.06), 421066
(1.05), Chingovu (0.94), 420014 (0.91), Excel (0.9), 199062.1 (0.87) and Unawazambane06-01
(0.81) gave higher FSR yields (kg plant-1) than the local checks. Genotypes Nyarmalo and
Polista were among the lowest yielding in the irrigated and non-irrigated conditions. Clones
W119, 441725, and Xiadla-xa-kau were the highest yielding under the drought stress
conditions.
The performance of 24 improved clones was evaluated in replicated trials at KARI-Thika and
KARI-Kiboko using 24 sweetpotato clones grown under managed drought stress conditions for
two seasons. AMMI, GGE biplots and regression analyses were conducted to determine
stability of the clones. Mean FSR was significantly different (P < 0.001) in the two research sites
with the environment contributing to 92.7% of the total variation, genotype 1.8%, and
interactions 0.4%. AMMI and GGE biplots, and regression indicated the most stable clones to
be 441725, Unawazambane06-01 and 189150.1, while Xiadla-xa-kau was the least stable.
To gather more information on drought tolerance mechanisms expressed in the sweetpotato
genotypes, an experiment was conducted in the greenhouse using clones expressing different
levels of drought tolerance in the field. The results showed more under-developed roots (pencil
roots) in the drought stressed regimes than in the irrigated regimes and in the drought
susceptible genotypes. Drought tolerant genotypes produced more FSR and NSR. The number
of vine branches (NVB), vine tip pubescence (VTP) and mature leaf pubescence (MLP)
increased with reduction of drought stress however, drought tolerant clones had reduced NVB.
Drought stressed clones had shorter basal vine length (BVL), reduced CC, and reduced leaf
growth (LG). Drought stress reduced growth of vines in terms of internodes length, internodes
diameter, vine length, petioles length, and leaf CC. Overall, for the first time, the study
demonstrated that drought stress in the first three months after planting, leads to the
proliferation of non-edible pencil roots, which do not become edible storage roots even when
drought stress is removed. Therefore, water is critical during this period for improved
sweetpotato storage root yield, probably as a drought tolerant mechanism.
Combining ability for yield and drought tolerance of 15 F1 sweetpotato families generated
through a half diallel mating of six parents was evaluated at KARI-Kiboko in 2012. Significant
(P≤0.05) general combining ability (GCA) and specific combining ability (SCA) effects were
recorded for root yield in both drought stress and no stress conditions, indicating that both
additive and dominance gene effects were important in the inheritance of resistance to drought
stress. Progenies from families G2, G5, G7, G8, G10, G12 and G15 had good SCA for fresh
storage root yield, total biomass, number of days to permanent wilting point (DPWP), harvest
index, and drought stress index (DSI). Progeny 8 from family G4, 5 and 8 from G15, had the
highest mid and best parent heterotic effect (117-270%) for fresh storage root yield in both
drought stress and no stress conditions. Progeny 6, and 7 from family G10, had the highest mid
and best parent heterotic effect (165-234%) for fresh total biomass yield under no drought
stress conditions. In conclusion, the progenies from families G2, G5, G7, G8, G10, G12 and
G15 that had high yield and biomass specific combining ability under drought and no drought
stress indicated that they could be having drought tolerant genes, and therefore could be
incorporated into advanced drought screening trials with the aim of releasing the best
performing drought tolerant varieties. Secondly, the findings in this study lay a foundation for
sweetpotato breeding programmes on drought tolerance. Thirdly, for the first time, this study
uniquely combines yield performance, combining ability estimates, days to permanent wilting
point and heterosis under contrasting moisture regimes to unmask the gene action of drought
tolerance in sweetpotato, a milestone in science. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Evaluation of selected sweetpotato (Ipomoea batatas) accessions for drought toleranceOmotobora, Babajide Olusegun 06 1900 (has links)
Sweetpotato (Ipomoea batatas) is a major staple food in Africa and the rest of the world where they are discovered to be a good source of carbohydrates, vitamin A, vitamin C and protein. The maximum production potential of the crop is being hampered by severe drought which ravages most parts of Africa.
The main aim of this project therefore is to screen collected accessions of sweetpotatofor drought tolerance in a quick screening method with a view to identify cultivars that can perform well under water stress conditions.
Fifty selected sweetpotato accessions consisting of cultivars and breeding lines collected from the ARC-VOPI gene bank were planted for drought screening in the glass house for 6 weeks during which water was withheld to induce stress. Observations were made on number of dead plants and days to wilting point, the results were analyzed and 12 best performing cultivars were selected for field trials.
The field trial was carried out in Lwamondo, Thohoyandou for 6months under rain-fed conditions. The experiment was conducted in a complete randomized block design with 6 replicates.Yield data and growth parameters were collected every 8 weeks during the trial period and the data collected was analyzed using ANOVA. The best performing cultivars were Zapallo, Tacna, Ejumula, 2004-9-2 and Ndou. They were therefore recommended for further evaluation in other drought prone areas of the country. / Agriculture and Animal Health / M. Sc. (Agriculture)
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Screening sweetpotato (Ipomoea batatas L.) for drought tolerance and high β-carotene content in Mozambique.Ricardo, José January 2011 (has links)
Sweetpotato (Ipomoea batatas, L.) is one of the important sources of carbohydrates and
economic income in Mozambique. As with most of the food crops in Mozambique, it is
usually produced by small-scale farmers under dryland conditions. Despite the importance
of the crop, the storage root yields are still low and it is difficult to keep planting material
(vines) for the next planting season. One of the major challenges to production is drought
stress. Drought stress affects sweetpotato by retarding aboveground growth, reducing total
root yield, percentage of dry mass, and reducing the quality of the roots as a result of the
increase in damage caused by the sweetpotato weevil (Cylas formicarius).
The objective of this study was to identify sweetpotato genotypes tolerant to drought
particularly amongst the orange fleshed types which can be used in breeding programmes
to improve the drought tolerance of genotypes grown in Mozambique. To this end, 48
genotypes were evaluated in both field and greenhouse studies conducted at Umbeluzi
Research Station (26º 03’ S, 32ºC 23’ E; 12 masl) located about 30 km from Maputo city.
The field trial was a three replicate, α-design with split-plots. Genotypes were the wholeplot
treatment factor and irrigation levels were the sub-plot treatment factor. The three
irrigation levels imposed were: nonstressed plants irrigated from planting to 120 DAP;
moderately stressed, plants irrigated until 60 DAP; and severely stressed, plants irrigated
until 30 DAP. In the greenhouse trial the 48 genotypes were grown in wooden boxes
arranged in a two replicate, randomized complete block design. The plants were exposed to
water stress from 10 DAP to the end of experiment at 60 DAP.
Genotypes were significantly different for all traits, namely: survival %, vine vigour,
aboveground biomass, total and commercial root yield, total fresh biomass, harvest index, β-carotene content, % dry mass, dry mass yield, incidence of sweetpotato virus disease,
and incidence of weevil damage. Irrigation levels were significant for the traits: survival
%, vine vigour, aboveground biomass, total and commercial root yield, total fresh biomass,
harvest index, β-carotene content, % dry mass, and dry mass yield. Irrigation levels were
not significant for incidence of sweetpotato virus disease and incidence of weevil damage.
The genotypes x irrigation levels interaction was significant for: total and commercial root
yield, and incidence of weevil damage; and not significant for: survival %, vine vigour,
aboveground biomass, total fresh biomass, harvest index, β-carotene content, % dry mass
composition, dry mass yield and incidence of sweetpotato virus disease.
The mean dry mass yields across irrigation levels of the national breeding lines and
introduced genotypes were higher than the landrace genotypes. Most of the national
breeding lines had higher β-carotene content than the introduced and landrace genotypes.
The landrace genotypes had relatively higher % dry mass composition compared to the
national breeding lines.
The stress tolerance index (STI) separated the 48 sweetpotato genotypes evaluated in the
field trial into three groups: drought tolerant (high STI); moderate drought tolerant
(intermediate STI); and drought sensitive (low STI). Under moderate stress, yield potential
(Yp) and yield in a stress environment (Ys) were highly significant, positively correlated
with Mean productivity (MP), Geometric mean productivity (GMP), Stress tolerance index
(STI) and Tolerance index (TOL). Under severe stress the same correlations were reported.
Under moderate and severe stress, the correlation between stress tolerance index (STI) and
Stress susceptibility index (SSI) was significant and negative. In the greenhouse trial, differences between genotypes in vine length increment, vine
diameter increment, leaf width increment and number of nodes vine-1 were significant
(P<0.05). Vine length, vine diameter, leaf width and length increments either increased or
were reduced due to water stress. Less than 10% increment in vine length (between 25 and
50 DAP) was recorded in MGCl01, Atacama, Cordner, Beauregard, and CN1448-49.
Higher than 40% vine length increment was recorded in Jonathan and UNK-Malawi,
Naspot, MUSG0614-24, Resisto, K566632, Tainung64, Ejumula and MUSG0623-09. Vine
diameter decreased in Manhissane and MUSG0616-18. No change in leaf length in Tacna
and Jonathan and in leaf width in Xihetamakote and Resisto-Nairobi was recorded.
The longest petiole length at 30 DAP was recorded by Tacna and the shortest by
Nhacutse4. The longest internode length was recorded in 199062.1. Similar to petiole
length, Nhacuste4 reported the shortest internode length. The highest number of primary
vines was recorded by MUSG0608-61 and lowest by Beauregard. Of the 48 genotypes
exposed to water stress, 18 survived until the end of the greenhouse experiment at 60 DAP
and were therefore considered to be drought tolerant. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, 2011.
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