SENSAKO, WELGEVALLEN EXPERIMENTAL STATION
Stellenbosch P.O. Box 3079, 7602 Matieland, Stellenbosch, South
Africa.
R. de V. Pienaar, Marizanne Horn, and A.J.G. Lesch.
Research to improve the efficiency of the `wheat
x maize' DH system was continued in 1995. A maize line
was developed by sibpollinating the F4 derivatives from
the maize hybrid `Seneca 60', which gave the best
results. This line, which gave up to 60 % haploid embryos (HEs)
per wheat spike (depending on genotype, season and hormone application),
was used as pollen parent on 12 spring wheat and 12 winter wheat
genotypes. Overall, 25,003 spring wheat florets (PFs) were pollinated
(when the most mature florets of the spikes began to open) and
filled with 50 different wheat haploidizer (WH) solutions containing
one or more growth regulators (GRs) 24ñ48 hours after pollination.
This resulted in 16,634 (= 66.5 % of PFs) green parthenocarpic
caryopses (GPCs) 16ñ21 days after pollination; 6,694 HEs
(= 40.2 % of GPCs, or 26.8 % of PFs) were excised from these GPCs.
By culturing these embryos on 20 different culture media, 1,014
plants (= 15.5 % of cultured HEs or 4.1 % of Pfs) were obtained.
The 3,984 winter wheat florets filled with six different WH solutions
produced 1,377 GPCs (= 34.6 % of PFs) of which 331 (= 24 % of
GPCs or 8.3 % of PFs) contained HEs. These were cultured on three
media and gave rise to 63 plants (= 19 % of HEs or 1.6 % of Pfs).
Following colchicine treatment (see our protocol in AWN
Vol. 40), more than 90 % of the spring and winter wheat plants
gave rise to DHs.
The three haploid-inducing GR solutions (wheat haploidizers
(WHs)) that gave the best results (> 30 % of PFs produced HEs)
in 1995 are:
1. WH10 = 30 mg/L picloram + 4 mg/L BA,
2. WH11 = 20 mg/L picloram + 15 mg/L 2,4D + 2 mg/L BA + 75 mg/LGA3, and
3. WH12 = 20 mg/L picloram + 25 mg/L 2,4,5T
+ 6 mg/L BA.
These picloram-based solutions produced better results
than the dicamba-based solutions used in previous years and were
superior to the standard 2,4D treatments. When the HEs
obtained by using the above WHs were cultured (in the dark for
the first week) at 25_C on the barley callus regeneration MS medium
of Dr. G. von Daniel (Freising-Weihenstephan, Germany) to which
1 mg/l IBA and 0.5 mg/l BA were added, 86 % developed into plants.
None of the other more complex media used gave superior results.
By using the above protocol, up to 12 haploid plants per spring
wheat spike were obtained.
The embryos were excised 20ñ22 days after
pollination when the wheat plants were grown in greenhouses with
a 14-hour photoperiod and a day/night temperature cycle of 18/12_C,
but 16ñ18 days after pollination when grown at 24/16_C
or higher temperatures.
SELIAN AGRICULTURAL RESEARCH INSTITUTE
P.O. Box 6024, Arusha, Tanzania.
Patchy stunting of wheat at the Hanang Wheat Complex.
Catherine Kuwite.
Patchy stunting of wheat (PSW) has occurred yearly
in the farms of the Hanang Wheat Complex since the early 1970s.
Mineral toxicities and deficiencies, poor soil structure, soil
aphids, termites, and nematodes, were ruled out as causal agents
of PSW. New attempts to identify the cause of PSW have focused
mainly on mycological factors. Random plant samples were taken
from the center and periphery of PSW spots and from healthy-appearing
areas. Isolations were made in the laboratory, and a number of
fungus genera were identified. The study showed that three fungi,
i.e., Rhizoctonia spp., Bipolaris sorokiniana,
and Fusarium oxysporum were associated with PSW-affected
plants. Rhizoctonia spp. produced sclerotia-like structures
(nodules) on lower roots of affected plants. More nodules appeared
at the center of PSW spots on dead plants than at the periphery.
Fewer nodules appeared on healthy-looking plants than at periphery
of PSW spots. Recent studies showed that Rhizoctonia spp.
are more prevalent on PSWaffected plants than the other
two fungi species and could be a major factor in the PSW syndrome.
Experiments are underway using the Rhizoctonia isolates
to prove Koch's postulates (from the Proceedings of the 9th Regional
Wheat Workshop, Addis Ababa, October, 1995).
Comparative performance of wheat and barley elite lines in Tanzania.
Mary Mgonja and Ibrahmi Mamuya.
Introduced bread wheat and barley genotypes were
evaluated during the 1992, 1993, and 1994 cropping seasons in
the national variety trial of each crop species. The principal
objective was to identify and select genotypes of each species
that would have a higher yield potential than the currently grown
varieties. The national variety trial for wheat had 25 lines
in 1992 and 30 lines in 1993 and 1994. The barley trial had 20,
22, and 25 lines in 1992, 1993, and 1994, respectively. Grain
yields for wheat were generally higher than those of barley, with
yields ranging from 2.2 to 3.7 t/ha versus 1.4 to 2.8 t/ha for
barley. All of the elite lines of both crops, except `Bima'
barley (local check), were in the early maturity group (45ñ65
days from seeding to 50 % flowering), an indication that such
lines match well with the seasonal availability of moisture.
The percent protein in wheat ranged from 11.2 to 13.1, and the
malt extract in barley was between 77.4 and 83.0 %. Application
of N fertilizer to wheat could be one of the possible reasons
for the higher grain yields observed. Information is needed on
whether N could be applied to barley to increase grain yield without
adversely affecting malting quality (from the Proceedings of the
9th Regional Wheat Workshop, Addis Ababa, October, 1995).
Screening and evaluation of wheat germplasm in northern Tanzania.
Elizabeth J. Maeda.
Over the period 1991ñ93, a total of 5,840
lines of spring bread wheat, durum, and triticale were introduced
and screened for yield, disease resistance, and general adaptability
at the Selian Agricultural Research Institute. Only 125 lines
were identified as having high-yield potential, disease resistance,
and adaptation to the various agro-ecological zones tested. The
selected lines were retested in replicated trials for 3 consecutive
years. Results showed that the selected entries varied in yield
and other agronomic characteristics. Seven of the entries selected
had lower disease severity with more resistant infection types
than the checks and remained constant over the years of testing.
Mean yields ranged from 2.5 to 2.9 t/ha. Lines W90019 and W90026
consistently outyielded the other lines tested, whereas W90047
had the lowest mean yield. All the selected lines out-yielded
the three check cultivars used (from the Proceedings of the 9th
Regional Wheat Workshop, Addis Ababa, October, 1995).
HANANG WHEAT COMPLEX
P.O. Box 96, Katesh, Tanzania.
Agronomic constraints to sustainable wheat production at the Hanang Wheat Complex.
Paul L. Antapa, P.M. Mchomvu, and B.D. Majanga.
Wheat production under rainfed conditions at the
Hanang Wheat Complex (HWC) in northern Tanzania started during
the mid-1970s. Lack of suitable wheat cultivars and poor weed
control were among the initial primary production constraints.
Current production constraints include soil erosion, low and
erratic rainfall, and lack of availability of an efficient and
reliable market for the wheat grain. Investigation into most
of the researchable problems at the HWC is being achieved through
collaborative research between the Hanang Wheat Complex Agronomy
Department, the Selian Agricultural Research Institute, and CIMMYT
(from the Proceedings of the 9th Regional Wheat Workshop, Addis
Ababa, October, 1995).
Prospective rotational crops at HWC.
There are seven state-owned wheat farms in Hanang District, in
the Arusha Region, with a total arable land area of about 28,000
ha. The seven farms are independent companies (collectively called
The Hanang Wheat Complex) under the National Agriculture and Food
Corporation, NAFCO. These farms grow wheat commercially under
a continuous cropping system. The mean wheat yield over the past
10 years was 1.58 t/ha. The need for rotational crops on these
wheat farms was realized during the early 1980s when research
on alternate crops was initiated at Selian ARI and the Hanang
wheat farms. Monoculture poses many problems, including land
degradation through soil erosion, plant disease build-up, the
development of weeds resistant to herbicides, and grain marketing
problems. Break crops studied include soybeans, sunflower, safflower,
flax, canola/rapeseed, haricot beans, and maize. However, because
of marketing constraints, adoption of these crops has not taken
place (from the Proceedings of the 9th Regional Wheat Workshop,
Addis Ababa, October, 1995).
Operational and economic sustainability of the
HWC. The Hanang Wheat Complex consists
of a cluster of seven farming companies and a service center,
CMSC, as an eighth unit. The first company, Basotu Plantations,
was started in l968. Although the five older farms attained the
targeted area of 4,000 ha of wheat production land, the two most
recent farms are still expanding. The mean grain yield for the
past decade was approximately 1.58 t/ha. These farms are estimated
to produce 80 % of the wheat grown locally, satisfying between
45 % to 50 % of the local demand. After Canadian aid ended in
mid 1993, the question often asked is `How are these farms
going to sustain themselves?' (from the Proceedings of
the 9th Regional Wheat Workshop, Addis Ababa, October, 1995).