AGRICULTURAL RESEARCH CENTER
P.O. Box 126, Wadmedani, Sudan.
M.A. Mahir.
Multiple regression analysis was used to develop equations predictive of the severity of leaf rust and stem rust of bread wheat ,and to estimate weekly cumulative urediniospore numbers of both rust species in New Halfa region. Equations were generated for three overlapping periods to identify and quantify biological and meteorological variables that might provide clues of high predictive value for development of disease epidemics. Analysis of the combined data showed that the derived multiple regression models varied with prediction period, prediction duration, and rust species. On the whole, progress in time (X1) invariably significantly contributed to variation observed in rust severity. Other significant variables were found to be components of atmospheric humidity: minimum RH (X4), maximum RH (X5), and hours RH > 80 % (X6), followed by maximum temperature (X3) towards the end of the growing season but for leaf rust only. Minimum temperature (X2) and wind speed (X7), generally, did not significantly contribute to variation in rust severity. Simple linear regression analysis of overall disease severity revealed that leaf rust and combined rust exhibited highly significant and positive relationships with progress in time from 15 Jan. to 31 March, whereas stem rust had a nonsignificant negative relationship. The combined influence of three biological variables, namely progress in time (T), wheat growth stage (GS), and weekly trapped rust spore numbers (WSN), accounted for only 53 and 21.4 % of the total variation in leaf rust and stem rust severity (DS), respectively. Studies with mechanical rust spore trapping (MRST) showed that 40 and 53.7 % of the total variation in P. recondita, and P. graminis weekly trapped urediospore numbers (WSN) can be explained by a function involving: progress in time (T), wind direction (WD), and presence or absence of wheat crop (C). Wind direction exhibited a significant (5-1 %) negative effect on P. graminis, but nonsignificant influence on P. recondita, WSN. The inclusion of wheat growth stage (GS) in the model did not significantly improve the explanatory power of the function. Analysis of MRST data collected over ten weeks, from 15 Jan to 31 Mar, indicated that 68.4 and 74.7 % of the total variation in P. recondita and P. graminis weekly trapped spore number (WSN), respectively, can be accounted for by a function involving: progress in time (T), wheat growth stage (GS), and disease severity (DS). The inclusion of wind speed (WS) as a fourth variable in the prediction model significantly (5 %) increased the amount of variation with leaf rust, and had no effect on stem rust spore counts.
Mohamed Salih Mohamed, Abu Elhassan S. Ibrahim, Asharaf M. Elhashim, and Izzat S.A. Tahir.
Wheat genotypic mixtures were studied for two seasons, 1997-98 and 1999-00, at the Gezira Research Station, Wad Medani, Sudan. Four agro-morphologically distinct commercial cultivars, Debeira, Condor, Argine, and Neilain, were compared with all two-way mixtures in addition to 3:1 and 1:3 ratios of Debeira and Condor. Means for grain yield were significantly different in the first season only. Plant height conferred a high competitive ability upon Neilain, the tallest cultivar, which suppressed admixture genotypes in both seasons. On the contrary, Debeira, being taller than Condor, was a poor competitor in 1 Debeira:1 Condor and 3 Debeira:1 Condor mixtures. However, in the second season, the same combinations out-yielded all other mixed stands. In the first situation, growth habit, rate and cycle, related to early flowering and maturity of Condor, were probably effective competitive factors. Reversal of mixture performance in the second season could be related to genotype-environment interactions of component cultivars. Although 1 Argine:1 Condor performance was second best amongst mixed stands in the first season, it was the poorest in the second season. The mix of 1 Debeira:1 Argine out-yielded all other mixed stands and was second best among all treatments in the first season, and ranked third in second season. The mixture out-yielded its component genotypes in both seasons. Although the increase in Debeira grain yield more than compensated for the loss in Argine, complementary competition was indicated.
Omer H. Ibrahim and O.S. Abdalla.
High temperature is a major environmental constraint that limits wheat cultivation in the tropical and subtropical environments. Nonetheless, considerable variability in bread wheat performance under heat stress conditions has been reported. In Sudan, the wheat growing season is short (i.e., 90-100 days). Farmers, particularly in the northern region, often delay wheat planting until December to January, exposing the crop to heat stress. Delayed plantings are usually associated with substantial grain yield losses, up to 86 % at farm level. A field study at Hudeiba, during 1995-96 to 1997-98 advised farmers on the selection of cultivars suited to their intended planting time. A set of 15 elite wheat genotypes was planted at optimum (mid November) and late (mid December) sowing dates. Results indicated that delaying sowing date by one month reduced grain yield by 27 %, and genotypes exhibited significant differential response to sowing date. Genotype HD2380 was superior under both early and late plantings. However, medium maturity cultivars, such as Seri 82, Debeira, and Wadi el Neil, should be planted at the optimum date, whereas early maturity cultivars, such as Condor, Nacozari, and Fang 60, perform best when late sowing is unavoidable.
Izzat S.A. Tahir, Abdalla B. Elahmedi, Abu El Hassan S. Ibrahim, and O.S. Abdalla.
A study was conducted for two seasons (1997-98 to 1998-99) at the Gezira Research Station Farm, Wad Medani, Sudan to estimate progress in genetic improvement of the grain yield of bread wheat in a heat stress environment and to identify changes in traits associated with grain yield improvement. Seven bread wheat cultivars of different origin released in Sudan during 1960 to 1990 were used. Results indicated that grain yield increased from 2,524 kg/ha in 1960 to 3,295 kg/ha in 1990. Linear regression of cultivar means on years of release showed an increase of 25.7 kg/ha/yr (r = 0.55, P < 0.01) in grain yield. This increase in yield was associated with increases of 0.19 g/yr in thousand-grain weight, 0.24 %/yr in harvest index, 0.19 days/y in grain-fill duration, and a reduction of 0.21 d/yr in duration to anthesis. The study established that considerable progress has been achieved in wheat improvement under heat stress, and that breeders have modified several associated traits while selecting for yield per se.
Mamoun I. Dawelbeit.
About 168,000 ha in the Gezira Scheme are sown annually to wheat. Wheat production is fully mechanized. Harvesting usually occurs during March and April. About 300 combine harvesters are involved in wheat harvesting. Almost all of these machines are privately owned. The most common type is the self-propelled combine harvester equipped with a 4.5-m, wide-grain header. One of the most serious problems of using combine harvesters is the high harvesting losses. About 18-20 % of the produced crop is estimated to be lost during harvesting. This high harvest loss costs the farmer, the scheme management, and the country. The objectives of this research project were to investigate causal factors affecting wheat harvest losses in the Gezira, to quantify these losses, and to propose a plan to minimize such losses. Research was conducted at the Gezira Research Station at Wad Medani for two seasons (1991-92 to 1992-93) to estimate the effect of time of harvesting on wheat harvesting losses. Total wheat harvesting losses are generally divided into preharvest, gathering and processing losses. Results showed that average total losses amounted to 2.6 % in the first season and 2.3 % in the second season. A project to reduce wheat harvest losses was started in 1993-94, involving four approaches: the first approach targeted farmers and involved extension, educational, and media activities; the second approach targeted combine operators; the third approach involved regulatory activities; the fourth approach included field surveys to estimate actual harvest losses and to detect its sources. The project ideas and efforts were highly accepted by the Gezira Scheme Management and the farmers. Adoption rates were very high. Results of the technical surveys showed excellent progress in reducing wheat harvest losses. Before the project, losses were estimated to be about 20 %. Survey results showed the majority of these losses were due to machinery operational factors and management of the combine harvesters. The total decrease in harvesting losses in the first three seasons was about 13.2 %, equal to about 96,100 t of wheat. The value of the amount of wheat saved could be estimated to be about 38.4 billion Sudanese pounds or about US $25.6 million.