Abdelbagi M. Ali

A full-length enriched cDNA library and expressed sequence tag analysis of the parasitic weed, Striga hermonthica

BackgroundThe obligate parasitic plant witchweed (Striga hermonthica) infects major cereal crops such as sorghum, maize, and millet, and is the most devastating weed pest in Africa. An understanding of the nature of its parasitism would contribute to the development of more sophisticated management methods. However, the molecular and genomic resources currently available for the study of S. hermonthica are limited.ResultsWe constructed a full-length enriched cDNA library of S. hermonthica, sequenced 37,710 clones from the library, and obtained 67,814 expressed sequence tag (EST) sequences. The ESTs were assembled into 17,317 unigenes that included 10,319 contigs and 6,818 singletons. The S. hermonthica unigene dataset was subjected to a comparative analysis with other plant genomes or ESTs. Approximately 80% of the unigenes have homologs in other dicotyledonous plants including Arabidopsis, poplar, and grape. We found that 589 unigenes are conserved in the hemiparasitic Triphysaria species but not in other plant species. These are good candidates for genes specifically involved in plant parasitism. Furthermore, we found 1,445 putative simple sequence repeats (SSRs) in the S. hermonthica unigene dataset. We tested 64 pairs of PCR primers flanking the SSRs to develop genetic markers for the detection of polymorphisms. Most primer sets amplified polymorphicbands from individual plants collected at a single location, indicating high genetic diversity in S. hermonthica. We selected 10 primer pairs to analyze S. hermonthica harvested in the field from different host species and geographic locations. A clustering analysis suggests that genetic distances are not correlated with host specificity.ConclusionsOur data provide the first extensive set of molecular resources for studying S. hermonthica, and include EST sequences, a comparative analysis with other plant genomes, and useful genetic markers. All the data are stored in a web-based database and freely available. These resources will be useful for genome annotation, gene discovery, functional analysis, molecular breeding, epidemiological studies, and studies of plant evolution.

Impact of wheat-Leymus racemosus added chromosomes on wheat adaptation and tolerance to heat stress

Adaptation of wheat (Triticum aestivum L.) to high temperatures could be improved by introducing alien genes from wild relatives. We evaluated the responses of wheat-Leymus racemosus chromosome introgression lines to high temperature to determine their potentiality for developing improved wheat cultivars. Introgression lines and their parent Chinese Spring were evaluated in a growth chamber at the seedling stage and in the field at the reproductive stage in two heat-stressed environments in Sudan. Optimum and late planting were used to ensure exposure of the plants to heat stress at the reproductive stage. The results revealed the impact of several Leymus chromosomes in improving wheat adaptation and tolerance to heat. Three lines possessed enhanced adaptation, whereas two showed high heat tolerance. Two addition lines showed a large number of kernels per spike, while one possessed high yield potential. Grain yield was correlated negatively with the heat susceptibility index, days to heading and maturity and positively with kernel number per spike and triphenyl tetrazolium chloride assay under late planting. The findings suggest that these genetic stocks could be used as a bridge to introduce the valuable Leymus traits into a superior wheat genetic background, thus helping maximize wheat yield in heat-stressed environments.

Physiological Response of Three Wheat Cultivars to High Shoot and Root Temperatures during Early Growth Stages

Abstract Understanding wheat (Triticum aestivum L.) response to high shoot/root temperature during the early growth stages is important for successful production in tropical and subtropical environments. This study examined the physiological response of wheat cultivars to high shoot and/or root temperatures during early growth stages. Three cultivars; Imam, Fang and Siete Cerros were grown in soil and hydroponically at three shoot/root temperatures (23/23, 23/35 and 35/35ºC for the soil experiment; and 22/22, 22/38 and 38/38ºC for the hydroponic experiment). Leaf dry weight and leaf area plant-1 were significantly decreased by high shoot/ root temperature (HS/HR, 35/35 and 38/38ºC) but was not affected by a normal shoot/high root temperature (NS/HR, 23/35 and 22/38ºC). The NS/HR (22/38ºC) and HS/HR (38/38ºC) treatments in the hydroponic experiment significantly decreased photosystem II quantum yield ( Φpsii), photosynthetic rate (Pn) and specific leaf area (SLA) compared with the normal shoot/normal root (NS/NR, 22/22ºC) temperature treatment. Chlorophyll accumulation was significantly decreased by NS/HR, but increased significantly by HS/HR in most of the measuring dates. The heat-tolerant cultivar, Fang, always had the highest chlorophyll content, Φpsii and Pn under all temperature treatments, while the heat-sensitive cultivar, Siete Cerros, always had the greatest reduction in these traits especially towards the end of the experiment. Imam and Fang responded to HS/HR in the hydroponic experiment by immediate and greater reductions in leaf dry weight, total leaf area and SLA during the first wk of the treatments compared with Siete Cerros. The response changed with the treatments duration such that Imam showed the least reduction and Siete Cerros was the most affected cultivar towards the end of the experiment. Thus, wheat cultivars differentially responded to high shoot/root temperature by reducing the leaf weight and area and hence accumulating more chlorophyll in the diminished leaves. The failure to undergo such changes led to significantly lower chlorophyll accumulation, Φpsii and Pn under high root temperature.

Evaluation of conventional and prolonged-swelling sodium dodecyl sulfate sedimentation tests for the prediction of bread wheat quality under heat stress conditions.

In non-traditional, heat-stressed environments, wheat breeding programmes were mainly concerned with the introduction and adaptation of high-yielding, heat-tolerant cultivars regardless of the end-use quality. For the recently developed quality-oriented markets, new cultivars should combine the above-mentioned traits with good grain quality to improve economic feasibility of wheat production in these environments. This study aimed to examine the suitability of the conventional sodium dodecyl sulfate sedimentation (SDSS) test for predicting bread-making quality and to evaluate the effectiveness of a prolonged-swelling SDSS test in improving the predictability of end-use quality under heat stress conditions. Conventional and prolonged-swelling SDSS volumes were measured from whole meal of 15 bread wheat genotypes grown for two seasons under two sowing conditions at Gezira Research Farm, Wad Medani, Sudan. Results of correlations of SDSS volumes with total and insoluble protein contents, mixograph peak height and mixograph descending slope indicated the suitability of the SDSS test in predicting bread-making quality under heat-stress irrigated conditions. However, the absence of significant correlations with some quality attributes, such as mixograph peak time and mixograph curve width, demonstrated the non-exclusiveness of the SDSS test for predicting all bread-making quality attributes. The prolonged-swelling SDSS tests did not improve identification of differences among genotypes over the conventional test despite similarly predicting some quality attributes and showing relatively small increases in the correlation coefficient magnitudes with others. SDSS after 10 min from settlement (SDSS10) showed strong correlations with all other SDSS volumes at various times and with most of quality attributes. This suggested that SDSS10 could be used for evaluation of bread-making quality in early generations of the breeding programme in the hot irrigated conditions of Sudan and similar environments.