ZAMBIA-CANADA WHEAT PROJECT
P.O.Box 420078, Mbala, Zambia.
Influence of seeding date on the growth and grain yield of wheat.
Mary V. Mugala-Mukwavi, S.P. Mooleki, and J. Siwale.
Research to establish suitable planting dates for
rainfed wheat (T. aestivum L.) in Zambia started
in 1978 and has continued in response to the flow of new germplasm
from the breeding program. Five sites were used for the sowing
evaluation trial. Cultivars respond differentially to planting
dates and locations. Wheat planted in December usually develops
an epidemic level of Helminthosporium sativum.
Low subsoil pH levels prevent deep root penetration because of
aluminum toxicity, particularly in northern Zambia. As a consequence,
when the rains finish early, the late planted crop suffers from
drought stress. The cultivar Coucal, together with other lines
under development, combine greater resistance to H. sativum,
better aluminum tolerance and can be sown successfully over a
longer time period (from the Proceedings of the 9th Regional Wheat
Workshop, Addis Ababa, October, 1995).
CROP BREEDING INSTITUTE
Department of Research and Specialist Services, P. O. Box CY550,
Harare, Zimbabwe.
The Department of Research & Specialist Services (DR&SS) wheat breeding program.
N.A. Mashiringwani.
The government wheat breeding program considers early
maturity and high yield to be desirable combinations for incorporation
into new spring wheat varieties. These traits will ensure viable
production of wheat under irrigated conditons during the winter
season. Availability of high-yielding and early-maturing cultivars
would (1) make farm operations more flexible, (2) improve farm
economic viability, and (3) lead to increases in overall wheat
production. Consequently, the DR&SS Wheat Breeding Program
emphasizes development of varieties with good milling and baking
quality, high yield potential under intensive irrigated conditions
(national on-farm average yield is 6.5 t/ha), earliness (<
125 days from emergence to physiological maturity), disease resistance
(primarily leaf and stem rust), and adaptability to a range of
production conditions in Zimbabwe.
The 1995 Wheat Advanced Variety Trial included two
trials, each with 20 advanced lines plus five standard commercial
varieties (Nata, Pote, Deka, Ruya, and Tokwe). Trail 1 consisted
of high-yielding, later-maturing genotypes, whereas trial 2 consisted
of earlier-maturing lines. The two trials, each a `5 x 5'
quadruple lattice with four replications per site, were planted
during the 1995 winter season (May-October) at five research
stations and at nine on-farm sites. Across the 14 sites, the
average planting date was 13 May, 1995. The average fertilizer
application rate of N-P-K was 172-70-40 kg/ha, respectively.
The average amount of irrigation water applied (rainfall being
negligible) was 446 mm. Average yield across sites, as determined
by the replicated `4 x 6.6 sq m' plots at each site,
was 7.3 t/ha. The five top-yielding entries for each trial, across
locations, are listed in Table 1.
The Zimbabwe Cereals Producers Association (ZCPA)
is gratefully acknowledged for its continued assistance, without
which the on-farm wheat variety testing program would not have
been possible. Sincere appreciation and acknowledgments are expressed
to Mr. Rob Franklin of Sisal Farm, Mutare, who over the years
has assisted the DR&SS Wheat Breeding Program in many respects.
Gratitude also is expressed to the Agricultural Research Trust
(ART Farm) and all the farmers who offered their farms for use
as variety testing program sites. Blue Ribbon Foods (Ltd.) and
National Foods (Ltd.) are thanked for their continued assistance
with industrial quality analyses. The Biometrics Bureau and other
government research stations and centers are thanked for their
continued assistance under these very difficult times.
Table 1. The five top-yielding entries at each trial from the 1995 Wheat Advanced Variety Trial.
______________________________________________________________________________________
1,000-kernel Plant
Yield weight Maturity height Ld
Line (t/ha) (kg/hl) (days) (cm) %
______________________________________________________________________________________
Trial 1 (Late, high yield).
02 S86073-5H-0H-3H-0G-1H-0G 7.9 78 126 96 2
09 S86073-5H-0H-3C-0H 7.8 76 130 101 2
08 S87230-4H-0G-3H-0G 7.5 77 128 101 5
11 NATA 7.4 75 130 101 4
14 DEKA 7.5 75 128 105 7
Trial 2 (early maturity).
14 DEKA 7.5 76 127 95 17
11 NATA 7.5 75 127 92 14
21 S89078-0H-0G-22H-0G 7.4 79 122 89 6
06 S89027-0H-0G-8H-0G 7.4 77 121 78 1
02 S89067-0H-0G-7H-0G 7.4 77 122 84 9
______________________________________________________________________________________
UNIVERSITY OF ZIMBABWE
Crop Science Department, PO Box MP167, Harare, Zimbabwe.
Effects of tillage system and soybean mulch on weed emergence and wheat yield.
A.B. Mashingaidze, O.A. Chivinga, and D. Mtetwa.
An experiment was conducted to evaluate the effects
of no-till, conventional tillage, and amount of soybean residue
on weed emergence and wheat yield at the University of Zimbabwe
campus and farm. Conventional tillage significantly reduced weed
emergence (P < 0.05) when compared to no tillage at the two
sites. The distribution of weed seeds in the soil profile explained
why more weeds emerged in the no-till treatment, with 72 %, 23
%, and 5 % of viable weed seeds found in the 0-5, 5-10,
and 10-15 cm soil layers, respectively, in the no-till
treatment. This result contrasted with an almost equal distribution
of viable weed seeds in the soil profile of the conventional tilled
treatment. A significant `soybean mulch x tillage'
interaction (P < 0.05) occurred. Soybean mulch significantly
suppressed weed emergence in the no-till treatment, but not under
conventional tillage. Conventional tillage had significantly
higher wheat yield (P < 0.05) at the University of Zimbabwe
campus, where weed infestation was high. Yield was similar under
both tillage systems at the University of Zimbabwe farm, where
weed infestation was relatively lower. High weed pressure in
the no-till treatment was responsible for the yield reduction
at the campus site (from the Proceedings of the 9th Regional Wheat
Workshop, Addis Ababa, October, 1995).
DEPARTMENT OF RESEARCH AND SPECIALIST SERVICES
Chiredzi Research Station, PO Box 97, Chiredzi, Zimbabwe.
E.Z. Nyakatawa and F.T. Mugabe.
The future of wheat (T. aestivum L.) production
in the south-east lowveld of Zimbabwe will largely depend on reduced
irrigation using tolerant genotypes. The effects of reduced irrigation
on yield and yield attributes of four released wheat cultivars
and two promising advanced lines were investigated at Chiredzi
Research Station in the south-east lowveld of Zimbabwe. The irrigation
levels were 100 % (control) and 75 % and 50 % below the normal
irrigation levels. The promising lines tested were S84 and S86,
and the released cultivars were Deka, Pote, Nata, and Ruya. No
significant differences (P > 0.05) occurred in days to flowering,
days to maturity, stand count, plant height ears/sq m, spikelets/ear,
and grains/ear among the irrigation levels. For the 75 % and
50 % irrigation levels, the 1,000-kernel weights were 11 % and
24 % less than that for the control, respectively. Seed yields
was 67 % less at the 75 % rate and 84 % less at the 50 % irrigation
level than that for the control. Days to flowering, days to maturity,
spikelets/ear, 1000-kernel weight, and grain yield were different
(P < 0.05) among the six genotypes. The effects of genotype
on the other parameters were not significant. Average grain yield
for the promising lines was 25 % greater than that of the released
cultivars (from the Proceedings of the 9th Regional Wheat Workshop,
Addis Ababa, October, 1995).
SEED CO-OP COMPANY OF ZIMBABWE
PO Box CH142, Chisipite, Harare, Zimbabwe.
Selection for high grain yield in bread wheat using attributes that are correlated with grain yield.
E.K. Havazvidi.
Six breeding populations of spring wheat crosses
were stratified into short and tall stature subpopulations at
advanced generations of segregation. These subpopulations later
were space-planted in the F6 generation. Single plants subsequently
were selected on the basis of low or high biomass yield, grain
yield, or harvest index. Single ear-to-row progenies of
the selected plants were grown and measured for the expression
of the three attributes. Only high-yielding, single-ear
progenies in each category, including those selected at random
from the base populations, were evaluated in replicated trials
at two sites. High to medium yield responses to selection were
obtained using biomass and grain yield in the short plant height
group. In the tall stature group, high to medium yield responses
to selection were obtained when harvest index was used as a selection
criterion. Randomly selected lines were inferior to the best
selections in the short height group, but performed similarly
to the best selections in the tall group, where lodging negatively
affected yield (from the Proceedings of the 9th Regional Wheat
Workshop, Addis Ababa, October, 1995).