Maize (Zea mays)
is the staple food in Zimbabwe. However its production is limited by poor
adaptation of commercial hybrid varieties to smallholder growing conditions.
Presently-grown hybrid varieties were developed under optimum conditions and
hence are not adapted to the smallholder farmers’ conditions. This has
resulted in yields as low as 300kg/ha in some instances in the smallholder
sector which occupies 91% of the semi arid areas of the country. Such low
yields are not economically viable when considering the high costs of farm
inputs and other production costs. The result has been high incidence of
planting of recycled hybrid seed and hence a further decline in productivity,
compromising household and national food security. As a result, the national
maize program has embarked on the development and evaluation of
ecologically-adapted open pollinated varieties (OPVs), which are a better
option for the smallholder farmer compared to recycled hybrid seed. Moreover,
OPVs have been shown to be more stable under stress conditions than hybrids.
In addition, OPVseed can be recycled with minimum yield decline and seed
production costs are lower than for hybrids.
In order to identify OPVs that are adapted to the different
agro-ecological zones of the country, on-station and on-farm screening of 36
OPVs from the national program and introductions from CIMMYT and other SADC
countries was begun in the 2000/01 season. This screening has resulted in the
selection of 12 OPVs which are better adapted to the nitrogen deficient soils
in the dry target regions of the country. The selected 12 OPVs will be
extensively evaluated on farms across the country using the community-based,
participatory approach known as the ‘Mother-Baby’ evaluation approach.
The ecologically-adapted OPVs will be identified and community based
seed production schemes initiated in order to make seed available to the
different communities. Use of the Mother-Baby screening procedure has led to
the release of two synthetics, namely, ZM421 and ZM521 for commercial
production. To further develop
new OPVs, sixty-five inbred lines and varieties were evaluated across the
semi-arid areas of the country after which the best adapted materials were
crossed in a diallel fashion. The resultant hybrids and varieties were
evaluated and the best combinations were initially used in the formation of
two synthetics which will be included in the set of entries to be evaluated
using the Mother-Baby scheme starting the 2002/03 summer season. This variety
development program is on going and the resultant OPVs/Synthetics will be
included in the screening process.
Evaluation
of cassava clones for yield, acceptability and disease and pest resistance in
coastal Kenya.
One hundred and fifteen (115) cassava clones were
evaluated on-station at two sites during the 2001growing season in coastal
Kenya for yield, acceptability and resistance to East African Cassava Mosaic
Virus Disease (EACMVD), Cassava Green Mite (CGM) and Cassava Mealybug (CMB).
The experimental design was a complete randomised block design with 3
replicates. Plot size measured 2m by 6 m. Cuttings were planted at a spacing
of 1 m by 1m. Data on symptom scores and visual incidence of plants affected
was recorded at 3 and 6 months after planting (MAP) used as index for
resistance. Harvesting was done 11 MAP at Mtwapa and 12 MAP at Msabaha. Data
were recorded on number and weight of marketable, unmarketable and total
tubers, dry matter (DM) %. At harvesting, farmers assessed the clones using
their own criteria. Clones for on-farm testing were selected on yield
performance, disease and pest resistance and farmer acceptability. Site,
clone, and the interaction between site and clone effects were significant
(P<0.01) for total and marketable roots per plot while clone effect was
significantly different for marketable yield (kg/plot). Clones performed
better at Msabaha than at Mtwapa. The best clones at Msabaha were 2001LML/2095
(197 total roots/plot), 2001LML/939 (98 marketable roots/plot) and
2001LML/1270 (73 total and 61 kg/plot marketable yield/plot). At Mtwapa, the
best clones were 2001LML/2095 (213 total roots/plot) 2001LML/1306 (84
marketable roots/plot) and 2001LML/1486 (65 and 59 kg/plot of marketable and
total yield, respectively). The highest % incidence for EACMVD, CGM and CMB
were recorded at 6 MAPS. The % incidence of EACMVD and CMB were higher in
Mtwapa than Msabaha. Farmers
assessed cassava clones based on yield, taste, dry matter content, root size
and number and ability of clones to produce a large amount of planting
material. Yield, taste and dry matter content influenced farmers to select
clones for market or home use. Farmers
selected 78 clones at Msabaha but these were reduced to 37 for further
evaluation after rejecting all clones with EACMVD, Cassava Brown Streak Virus
Disease, and severe scores of CGM and CMB.
Breeding climbing beans
resistant to angular leaf spot, pythium root rots and fusarium wilt
A. Musoni,
R. Buruchara & P. Kimani
Beans
(Phaseolus vulgaris L.) are an
important source of dietary protein in east and central Africa.
In Rwanda, beans supply 65% of dietary protein. New, improved and high
yielding climbing bean varieties selected using farmer participatory
approaches and released in early 1990’s had by 1995 been adopted by 47% of
households. Productivity of beans at farm level increased by 250%,
particularly in high potential zones of northern Rwanda.
The most widely adopted cultivar (by 80% of farmers) was Umubano
(G2333) because of its superior agronomic, culinary, market qualities, yield
potential (4 to 4.5 ton ha-1,) and resistance to anthracnose.
However, due to its high susceptibility following an outbreak of Fusarium
wilt in late 90’s, many farmers abandoned growing Umubano. Similarly,
susceptibility of traditional and new climbing bean varieties to angular leaf
spot and Pythium root rot diseases meant that the high yielding potential of
the climbing beans in the Great Lakes Region of central Africa could not be
fully realized. Previous evaluations had shown that Vuninkingi (G685) and Flora
were resistant to F. oxysporum, SCAM
80 CM/15 and RWR 719 resistant to Pythium root rots, and MEX 54 to angular
leaf spot. The objective of this research was to improve and to develop well
adapted high yielding climbing bean varieties combining resistance to the
three diseases in preferred seed types. Consequently, multi-parent crosses
were made in several combinations using Umubano,
Ngwinurare and Vuninkingi as popular and adapted parents and MEX 54, Vuninkingi
and SCAM 80 CM/15 as sources of disease resistance. F2 progenies
were screened for resistance based on natural infestation in disease hot
spots. This will be followed by artificial inoculation of selected
materials in a screenhouse. Recombinants for resistance to angular leaf spot,
fusarium wilt, Pythium root rots and anthracnose will be selected. Studies on
the nature of inheritance of resistance to Fusarium wilt are also in progress.
Development
of highland banana cell suspension system: A critical stage in genetic
improvement of the banana
P. Namanya,
G. Mutumba, S.M. Magambo, W. Tushemereirwe
The East African highland banana, the most important
staple food in Uganda, is susceptible to a range of pests and diseases. This
has been attributed to a limited genetic variation of the banana group.
Development of resistant genotypes using a genetic transformation approach has
been identified as a potential option to explore. The initial objective was to
establish a system to generate embryogenic cell suspensions for East African
highland bananas. Cell suspensions are the material of choice for genetic
transformation of banana because of their regeneration capacity through
somatic embryogenesis. Immature male flowers were used as explant source.
Embryogenic callus with somatic embryos and friable tissue was obtained
after a culture period of 4 months on callus induction medium designated M1.
Subsequent cell suspensions were initiated and maintained in liquid
medium MA2 (Cote et al., 1996). The
cells in suspension were embryogenic and a cell growth rate of 1.5-2.0 scv per
month was observed. The embryogenic cell suspension stage is critical for
introduction of genes of resistance into the bananas.
Regeneration produced up to 2.18x102 embryos per 0.05-0.1ml
scv. Germination of these embryos was observed at 2.78% and 3.27% for two cell
suspension lines. Plantlet recovery was 60-100%, all being normal, plants with
root and shoot at weaning. This study clears the key hurdle to application of
genetic improvement of East African highland bananas using genetic
transformation approaches.
Heterosis in
maize hybrids: Fact or artifact
J.A.W. Ochieng
Heterosis (hybrid vigor) is defined as the superior
performance of the hybrid cross over the mid-parental value.
For topcross progenies, using a common tester, heterotic level narrows
down to the performance of the female parent relative to the hybrid.
Topcross hybrids of maize were evaluated for heterosis in a replicated
trial at two sites in one season following standard agronomic practices for
Kenyan highlands. The
tester (male parent) was an improved maize population at cycle 10, whilst the
female parents were either landraces, improved populations or inbred lines.
Mid-parent heterosis was computed for grain yield (T Ha-1), ear height
(meters) and days to 50% anthesis. Statistically
significant differences (p< 0.05) among varieties were observed for all
traits, except plant stand. Heterosis
varied among hybrids for the three traits.
Heterosis was positive for grain yield and ear height, but negative for
number of days to 50% anthesis. There
was a range in variation of heterosis levels for grain yield, ear height and
days-to-anthesis. For grain
yield, high percent heterosis was associated with those topcross hybrids in
which the female parent was an inbred line or an ill-adapted landrace,
implying that the high value was an artifact of the low yield potential of the
landraces or inbred line cross, compared to the hybrid.
Generally, percent heterosis for yield was lower in the hybrids in
which the female parent was either a single cross or population well-adapted
to the highlands and in this latter case, heterosis was considered a genetic
fact.
Interactive
maize breeding for biotic stresses across ecosystems in Kenya
O.M. Odongo,
S.I. Ajanga, C.M. Mburu & J. Ininda
Maize in Kenya is affected by a number of biotic
stresses which vary in their effect on grain yield depending on the season and
agro-ecological zones. Major
among theses stresses are northern leaf blight caused by Exserohilum turcicucum, maize streak virus transmitted by leaf
hopper, rust (Puccinia sorghi), grey
leaf spot (Cercosporazeae maydis),
stalk/ear rot (Diplodia maydis and Fusarium
spp.), stalk borer and weevils. The
most economic means of minimizing losses from these stresses is through
resistance breeding. The
development of a variety resistant to all these stresses by one breeding
programme will not only be very expensive, but will also be very demanding in
expertise being available in a given programme.
It is in this respect that an interactive breeding approach was
initiated in Kenya to take advantage of maize germplasm, equipment, ecology,
and expertise found in different Kenya Agricultural Research Institute (KARI)
Centres. The Centres involved were Kakamega, Muguga, Embu, Kitale and
Katumani. The Centres were
grouped on the basis of common biotic stresses.
These groupings linked Embu, Muguga and Kakamega Centres where blight,
grey leaf spot, maize streak, stalk borer and weevil are major biotic stresses
with varying magnitudes in their mandate areas. Screening and selection of inbreds for various stresses was
done at each Centre, emphasizing the major stresses in specific ecologies and
thereafter there was exchange of information and germplasm.
Such information and germplasm were used in developing maize hybrids
that have passed through the Kenyan variety testing system and are in the last
stages of variety release system, having gone through preliminary yield trial,
advanced yield trial, national performance trial and on-farm trial.
The paper presents data on the selected varieties at various test
stages. The data is on grain
yield, major biotic stresses scores, plant height, maturity and standability.
Four hybrids have been developed at KARI Kakamega and are ready for
release to farmers due to their superiority over available checks for biotic
stresses and grain yield. The varieties are KM 2001, KM 2012, KM 2013, KM2023, with
grain yields ranging from 7 - 10 tonnes per hectare compared to the commercial
checks Phb3253 and H622 which had grain yield ranging from 5 - 6 tonnes per
hectare.
Breeding
weevil-resistant maize: Is it feasible?
K. Pixley,
T. Dhliwayo & S. Munjoma
Maize weevil (Sitophilus
zeamais) causes extensive damage to stored maize (Zea mays), particularly to grain stored on-farm without chemical
protectants. Breeding of maize
varieties with improved weevil resistance, however, is not practiced to any
significant extent, because of uncertain probability of success and because
seed producers generally consider storability of grain to be outside of their
responsibility. The Rockefeller
Foundation-funded Weevil Project, at CIMMYT, has guided a total of four
graduate students through a progression of studies investigating the genetics
of weevil resistance and exploring practical methods for breeding maize with
increased resistance to weevil. Important
milestones within the five years of the project have been: 1) Identification
of significant genetic variation for weevil resistance among
regionally-adapted maize germplasm, 2) Investigations of secondary traits for
use in selecting maize with weevil resistance, 3) Successful divergent
selection for weevil resistance in several maize populations, and 4) Ongoing
investigations of per se resistance
relative to hybrid performance for maize lines at various levels of
inbreeding. This paper will
summarize recent results, describe on-going work, and offer recommendations
based on our current understanding of this important challenge. It is clear from results to date that breeding for improved
weevil resistance is possible; it remains unclear, however, what breeding
method(s), if any, are practical, effective and feasible for widespread use in
maize breeding programs.
Characterization
and use of diversity within guinea-race
sorghums
F. Rattunde, A. Toure, E. Weltzien
& D. Sansan
Guinea-race
sorghums originated in the W.African Savanah.
They are critically important for food security and account for 50% of
all sorghum produced in Africa. This
race is “rustic” with outstanding adaptation, plant heights of 3-5m, and
total biomass yields up to 10 t/ha. Grain
yields, however, respond poorly to intensified production conditions. The
challenge is to use the diversity within this race to increase yields while
maintaining the adaptive characteristics.
An improved understanding of the structure of diversity within this
race will enable more effective use of this germplasm for developing source
populations, varieties and hybrid parents.
A Guinea-race core collection
of 293 accessions was formed from the 3907 Guinea
Accessions in the ICRISAT Sorghum Collection using principal components
analysis with 9 quantitative traits (flowering dates, plant height, peduncle
exertion, panicle width and length, grain size and seed weight).
This core collection was evaluated for key agronomic characteristics in
Mali. Diversity was observed for all traits.
Plant heights ranged from 1.3 to 5.5m, panicle lengths from 20 to 61cm,
and thousand grain weights from 4 to 36. No major differences were observed
between geographic regions (Western and Central-, Eastern and Southern Africa,
Asia) as most of the variation was within regions. Within regions some
patterns of diversity appeared. For
example a higher frequency of accessions with large grain size were observed
from Cameroon and Malawi. To
characterize the core collection for fertility reaction on A1 cytoplasm for
hybrid parent development, a sub-set of 62 accessions were crossed onto
male-sterile lines and the F1s tested in Mali and Burkina Faso.
Thirteen accessions showed maintainer reaction, 38 restorer reaction and the
remainder showed predominantly partial fertility. Considerable plant-to-plant
variability occurred within accessions. Whereas more than 40% of accessions
from Burkina Faso and Senegal showed maintainer reaction, only restorer
reactions were observed among accessions from Nigeria, Cameroon and Asia.
This initial characterization information suggests possible starting
points for more detailed evaluations. Accessions with targeted traits, such as
large grain size, could be used directly in variety and hybrid parent
development, or introgressed into a newly created Dwarf Guinea-race
random-mating population to establish trait specific source populations for
targeted environmental zones.
Sources
of resistance to seed transmission and variation in responses of cowpea
varieties to infection by four seed- borne viruses
S.A. Shoyinka,
M.A. Ittah, I. Fawole & J.A. Hughes
Cowpea (Vigna
unguiculata L. (Walp)) a major food legume and a versatile crop grown in
many regions of the world, is susceptible to more than 20 viral diseases
world-wide. Some of most
destructive of these are transmitted through the seed and are thereby
disseminated to most cowpea–producing regions of the world.
The most effective control of cowpea viral diseases has been the
development of improved genotypes with resistance to viral infection.
A field and screenhouse investigation was conducted at IITA, Ibadan,
Nigeria to identify sources of resistance to seed transmission and variation
in responses of 15 cowpea varieties to infection by four seed-borne viruses:
bean common mosaic potyvirus (blackeye cowpea strain: BCMV-BIC), cowpea
aphid-borne mosaic potyvirus (CABMV), cowpea mottle carmovirus (CmeV) and
southern bean mosaic sobemovirus (SBMV).
The varieties were mechanically (sap) inoculated at the field at the
seedling stage while seeds harvested from such plants were sown in seed trays
in an insect-free screenhouse to determine percentage seed transmission of
each virus. Protein – A
sandwich Enzyme–linked immunosorbent assay (PAS-ELISA) was used to detect
the presence of virus in test seedlings.
Disease severity was scored on a 5-point visual estimation scale.
Infection incidence was the proportion of infected plants to the total
number of plants in a plot. There
was considerable variation in rates of seed transmission and disease severity
caused by each of the four viruses. CMeV infected significantly more varieties
(14) and induced more severe symptoms in them than did BCMV-BIC (13), CABMV
(12) or SBMV (7) respectively. Rates of seed transmission also varied
depending on the variety/virus combination.
In the susceptible varieties the severity of infection at 6 weeks after
inoculation (WAI) was significantly higher than at two WAI (p<0.05).
Conversely, resistant varieties showed significantly less severe
disease at 6 WAI than at 2 (p< 0.05).
Disease severity index was not correlated with seed transmissibility of
a virus through seeds of an infected variety.
There was significant variation among the varieties in loss of
germinability due to infection by the viruses. CMeV reduced percentage germin
ability in six varieties, BCMV-BIC in four, CABMV and SBMV in one variety
each. BCMV-BIC induced more
significant effects on many of the yield parameters measured such as number of
pods per plant, plant height, number of seeds per pod, weight of 100 seeds pod
growth and rate and total grain yield compared to CMeV, CABMV and SBMV in that
order. None of the 15 varieties was resistant to all the four
seed-borne viruses. Those
identified as being resistant to one or more of the viruses can be used in
developing elite lines that are less susceptible to seed–transmission thus
encouraging germplasm exchange across international boundaries.
Establishment
of an insectary and advances in rearing of maize stemborers at KARI, Katumani
J.M.
Songa & D. Mutisya
An insectary was established at the Kenya
Agricultural Research Institute (KARI) research station, Katumani in Machakos,
Kenya, in 1999, and has improved significantly over the years in its scale and
quality of operation. The
main purpose of this facility is to provide stemborers for use in
resistance-screening studies, insect bioassays and for oviposition/feeding
preference studies within KARI projects.
The stemborers that are reared are: Chilo
partellus (Swinhoe), Chilo
orichalcocilliellus Strand, Eldana
saccharina Walker (Lepidoptera: Pyralidae), Busseola
fusca Fuller and Sesamia calamistis
Hampson (Lepidoptera: Noctuidae), with the bulk of production being for the
first two species due to their relatively higher demand for use in resistance
screening studies. The
insectaries, the rearing procedures used, problems encountered during rearing
and the coping strategies are described.
The stemborer supply has increased with time from 26,000 in the long
rains (LR) 2000, to 961,689 stemborers in the long rains 2001. There have also been improvements in the quality
of production, record keeping and in the supply system in terms of synchrony
of the stemborer supply with the end-uses.
As part of the efforts to improve the rearing techniques, a laboratory
study was conducted to compare the survival to pupation stage of B.fusca larvae in large plastic jars (16 x 7.5 cm - 250 ml of diet -
20 larvae) compared to glass vials (7.5 x 2.5 cm - 15ml of diet - 1 larva).
There was no significant difference in the survival to pupation of
larvae reared in plastic containers (80.5%) and glass vials (85.2%).
Since plastic container saves on the time of infestation (egg batches
can be used), is less breakable and cheaper, it has now been adopted for the
rearing of B. fusca at the Katumani
insectary. Future plans on
improvement of the rearing facility, production, and the techniques used, are
discussed.
Participatory
plant breeding in Africa: A framework for understanding diverse approaches and
results achieved
L. Sperling
Participatory
Plant Breeding (PPB) is a relatively new approach to germplasm development,
with most PPB programs having been initiated within the last 10 years.
While some may argue that commercial, private-sector, plant breeding
has long been client-driven, or “participatory”,
PPB, when used to reach poor client groups to breed for heterogeneous
conditions, and to incorporate specialized client preferences leads to
fundamental changes in how plant materials are bred and selected by formal
breeding programs and farming communities.
This paper proposes a framework for relating different PPB approaches
to different outcomes and impacts. Drawing on 110 field programs worldwide and
focusing on case experiences from 16 African countries (presented at an
Africa-wide PPB symposium funded by RF in May 2001) the paper suggests some of
the wide variability of PPB programs. It
lays out the key variables for discriminating among PPB approaches and the
type and range of impacts achieved. These
include: the institutional context, the bio-social environment, the kind of
participation sought and the goals originally set.
While the paper’s core is ‘current trends in Africa PPB”, it ends
by presenting the next step: recommendations of an Africa-based PPB working
group. These embrace
institutional, technical and social action-based challenges.
Guinea
sorghum hybrids: bringing the benefits of hybrid technology to a staple crop
of Sub-Saharan Africa
A. Toure, F. Rattunde, D. Sansan &
E. Weltzien
Guinea sorghums predominate throughout the Savannah
sorghum belt, accounting for more than 70% of all sorghum grown, and for more
than 90% in the 600+ mm rainfall zone. The guinea sorghums are characterized
by high food grain quality, weathering and insect resistance, good grain
storage, and good adaptation to poor soils. Considerable efforts have been
made to breed higher-yielding sorghums using exotic non-Guinea germplasm. The
varieties and hybrids based on exotic germplasm, however, did not prove to be
a viable option in this zone except for special niche conditions. The use of
hybrid vigor offers the potential to achieve significant productivity gains
but has not yet been explored due to the lack of hybrid parental lines of
Guinea background. This project is developing maintainer/male-sterile (AB)
pairs of Guinea background and beginning to characterize the levels of
heterosis and combining ability within this race. The genetic materials used
include landrace varieties identified by researchers on the basis of higher
productivity, stability of yield over multi-environment tests, panicle
progenies selected by farmers within their own varieties, breeding lines from
the IER pedigree program, and the Guinea core collection. More than 300
testcross F1s of Guinea-race landraces and lines crossed with A1 cytoplasmic
tester lines were made and evaluated for their fertility reaction in Mali. The
results showed that more than half of all varieties tested showed maintainer
reactions. A total of 24 lines were identified that showed good maintainer
reaction. Large intra-varietal (plant-to-plant) variation for fertility
reaction exists, especially within the landrace varieties.
Uniform restorer reaction was shown by 7 varieties.
Good frequencies of both maintainer and restorer reactions occur among
Guinea-race sorghums from West Africa and should facilitate the development of
hybrid parents. Significant
progress was made to develop male-sterile lines from the maintainer lines
identified. The fourth backcross generation was completed for CSM 335(2
lines), CSM 207 (15), CSM 219 (11), and Fambé (2). The third backcross
generation was completed for IPS 0001 (5), 98-BE-F5P-82 (5), 97SB-F5DT-150
(5), and 97-SU-F5DT-151 (1). The establishment of two off-season generations
using dark cages to obtain flowering accelerated the breeding process,
enabling the production of A/B male-sterile pairs in the backcross 5
generation in less than three years. Trials are being initiated to determine
the heterosis levels and characterize combining ability among diverse
guinea-race accessions from a Guinea core collection. The parental lines
represent western, eastern and southern Africa as well as Asia.
They also have contrasting grain size, panicle architecture, plant
height, and maturity. Future research should broaden the genetic base of
hybrid parents using agronomic trait characterization data and molecular
genetic characterization of the structure of genetic diversity within the
Guinea race. The identification of heterotic patterns and development of an
ideotype(s) for guinea-race hybrid parents will facilitate efficient hybrid
development.
Towards
improved East African highland banana genotypes with resistance to pests and
diseases
W.K. Tushemereirwe,
M. Pillay, M. Batte, T. Ssali, D. Talengera, K. Nowakunda, J. Namaganda &
A. Kiggundu
Banana is the leading food and cash crop in Uganda.
It is estimated that about 9.5 million metric tonnes are produced
annually from about 1.5 million hectares representing 38% of cultivated land.
This level of productivity (6.3 tons/ha/year) is extremely low when compared
to the yields obtained on station (60 tons/ha/year). The severe productivity
decline has been attributed to pests (weevils and nematodes) and diseases
(black Sigatoka, banana streak virus and banana bacterial wilt) as well as
soil fertility decline, socio-economic problems and limited utilization
options. Genotypes with pests and disease resistance were identified as the
highest priority technology to be developed for control of the pests and
diseases. It is estimated that yields of highland bananas can be doubled by
using host plant resistance alone. Efforts
(joint between NARO and IITA) to develop resistant genotypes using
conventional breeding started in 1994. The initial objective was to assess the
potential of improving the banana group through conventional breeding. This
was achieved through crossing the different banana cultivars with a diploid
male parent (Calcutta 4) to identify female-fertile parents that could be used
in the breeding programme. About
50% of the 60 cultivars tested were female fertile. On-station evaluations of
the progeny from the above cross for resistanc to black Sigatoka and
acceptable cooking attributes yielded 16 promising hybrids. 4 of the hybrids
had cooking attributes in the range of the highland banana controls. This
suggested that any improved male parent was likely to result in some hybrids
with disease resistance and acceptable cooking attributes. As a result of this
information, a breeding approach involving 3X (female fertile, triploid
highland banana cultivars) by 2X (improved diploid male parents) and 4X (tetraploid
hybrids) by 2X (improved diploid male parents to get 3X (secondary triploids)
was adopted. This paper elaborates the progress towards an improved highland
banana genotype.
Regional
disease nursery (REGNUR): A unique opportunity for developing
multiple-disease-resistant maize
B. Vivek,
K. Pixley, O. Odongo, J. Njuguna, J. Imanywoha, G. Bigirwa & A. Diallo
Maize is grown on 15 million ha in eastern and
southern Africa. Several
diseases, like streak virus (MSV), grey leaf spot (GLS) and turcicum leaf blight (TLB) are of common occurrence in the region
and can result in complete crop failure.
With funding from The Rockefeller Foundation, a regional disease
nursery (REGNUR) project was initiated in 1998 to promote and enhance regional
collaboration to address the common disease and insect problems of maize.
The REGNUR project aimed to identify and increase access to disease
resistant germplasm, generate and disseminate information on disease and
insect resistance sources, and facilitate National Programs to develop
resistant varieties. A recent
REGNUR project was a diallel mating among 12 elite inbred lines identified by
REGNUR collaborators. The trial
was grown at 12 sites during 2001. Results
from 6 locations show that both general combining ability (GCA) and specific
combining ability (SCA) effects were highly significant for GLS, MSV, head
smut, Phaeosphaeria Leaf Spot (PLS),
turcicum and rust (P. sorghi), whereas only GCA was important for ear rot resistance.
On average, GCA determined 69% of resistance to diseases while SCA
determined 63% of variation for grain yield.
This implies that the approach to developing multiple disease
resistance should involve identifying lines with good per se resistances to
diseases with final selection for good combining ability for yield.
Correlations between GCAs for disease scores were generally
non-significant. This underlies
the need for screening specific diseases using artificial inoculation or
reliable “hot-spots” and highlights the importance of a project like
REGNUR, which enables such collaboration.
Details of the above results and findings from the concluded first
phase of REGNUR will be presented.
Regional
germplasm development and deployment for sustainable production and
utilization within the cassava sub-sector
J.B.A
Whyte, B.W. Khizzah, A. Dixon, N.M. Mahungu, P. Ragama, P.
H. Ojulong
Lack of food security for a large segment of the
sub-region’s population continues to exacerbate poverty and malnutrition.
The high population growth, HIV effects on the productive labour force,
degradation of environment, poor agricultural development support services and
lack of enabling economic policy environment has aggravated the situation.
Cassava has great potential and can play a critical role in contributing to
food and nutritional security, income generation, poverty alleviation and
socio-economic growth of the sub-region. The major diseases and pests that
plague cassava production in these ecologies include; cassava mosaic diseases,
bacterial blight, Anthracnose, mealy bug, green mite, nematodes and termites.
Yield losses of 80 to 100% could be attributed to a combination of these
biotic stresses. Fungal infection and a wide range of insects and other
microorganisms during processing and handling may lead to the formation of
mycotoxins making chips unable to meet trade and health standards. The larger
grain borer (Prostephanus truncatus
(Horn)) is currently the most serious pest of dried cassava in storage causing
weight losses as high as 70% after four months of storage. Lack of clear-cut
policies for the development of the sub-sector has also contributed to low
production of cassava in the region. In
collaboration with its partners a germplasm development and deployment
strategy for sustainable production and utilization within the cassava
sub-sector was established in Uganda, Kenya and Rwanda to generate improved
populations with desired characteristics targeting different end uses/markets,
avail the populations to partners for evaluation and selection under specific
agro-ecosystems and establish special backup populations. The scheme
comprising of sib-family seedling nursery, clonal characterisation and
performance evaluation, has ensured that the improved populations have the
necessary resistance/tolerance background to the major biotic stresses, and
good agronomic and root quality characteristics. Use of open quarantine
facilities has enabled the introduction of improved clones into Kenya,
Tanzania, Rwanda, Burundi, D R Congo, Southern Sudan and Mozambique with
significant reduction in the cost of exchanging cassava using tissue cultured
material. It has also shortened the time required for release of a variety by
approximately three years. The
clones have formed the basis of multi location and farmer participatory
evaluation and multiplication in these countries.
This process has enriched the cassava genetic base of the national
germplasm collection and under the current epidemic situation has provided a
highly efficient regional solution for the cassava farming community. The
farmer participatory approach to cassava evaluation has permitted rapid
assessment of large numbers of improved clones, facilitated greater
researcher-farmer collaboration, and enabled the network to target stable
genotypes across the region.
