Drought resistance and root morphology in sorghum

Two 2 m³ plots of soil were prepared to different water contents and each isolated from surrounding soil by impermeable plastic material. Nine sorghum varieties were germinated in the plots and allowed to grow without further watering. Time-to-wilt after emergence was measured, and several parameters relating to water flow of the seedling and nodal roots were determined. There was a good positive correlation between both seminal root and nodal root relative conductvity and time-to-wilt. In a second experiment, plants were germinated and grown in pots, and after two weeks of growth without further watering were inspected for survival in the unwilted state. The per cent survival was calculated. There was a negative correlation of seminal root relative conductivity with per cent survival, and a high negative correlation of the number of seminal roots with per cent survival. It is concluded that high relative conductivity indicates drought resistance if the plants are growing with less restricted roots as in open soil, while if the plants are grown in pots the reverse is the case. Experiments linking root conductivity with survival conducted in pots are poor predictors of performance in less restricted rooting conditions.     

Heat shock proteins in Sorghum bicolor and Pennisetum americanum I. genotypic and developmental variation during seed germination

Abstract The capacity to synthesize heat shock proteins (HSPs) during seed germination of sorghum (Sorghum bicolor) and pearl millet (Pennisetum americanum) has been examined. HSP synthesis is detectable in a thermotolerant genotype of sorghum during the first hour of imbibition of the seed under high temperature stress. A non-coordinate control of HSP synthesis during germination was revealed. Genotypic differences were manifest in the stage of germination at which the ability to synthesize HSPs was first apparent and this related to the thermosensitivity of that genotype.     

Molecular responses of plants to an increased incidence of heat shock

Abstract. Climatic change as a result of the greenhouse effect is widely predicted to increase mean temperatures globally and, in turn, increase the frequency with which plants are exposed to heat shock conditions, particularly in the semi-arid tropics. The consequences of extreme high-temperature treatments on plants have been considered, particularly in relation to the synthesis of heat shock proteins (HSPs) and the capacity to acquire thermotolerance. The heat shock response is described using results obtained with seedlings of the tropical cereals, sorghum ( Sorghum bicolor ) and pearl millet ( Pennisetum glaucum ). A gradual temperature increase, as would occur in the field, is sufficient to induce thermotolerance. The synthesis of HSPs is a transient phenomenon and ceases once the stress is released. Despite the persistence of the HSPs themselves, de novo synthesis of HSPs is required for the induction of thermotolerance each time high temperatures are encountered. The effect of a repeated, diurnal heat shock was investigated and genotypic differences found in the ability to induce the heat shock response repeatedly.     

A reappraisal of sterol biosynthesis and metabolism in aphids

Aphids of Schizaphis graminum (Rondani) (biotype C) reared on its host-plant, Sorghum bicolor (L.) Moench, sequestered campesterol, stigmasterol and sitosterol. Aphids reared for 72 hr on holidic diets supplemented with [4-¹⁴C]-sitosterol contained both [¹⁴C]-sitosterol and [¹⁴C]-cholesterol, indicating that these aphids are capable of dealkylation at C-24. When aphids were reared on artificial diets containing [2-¹⁴C]-mevalonic acid, no detectable amounts of radioactively labelled desmethyl sterols, nor metabolic intermediates in sterol synthesis (i.e. squalene, 2,3-oxidosqualene, 4,4-dimethyl and 4-monomethyl sterols) were found to accumulate in their tissues. The relevance of these findings to previous research suggesting the ability of aphids, via their symbiotes, to synthesize sterols is discussed.     

Response of no-till and conventionally planted grain sorghum to weed control method and row spacing

Grain sorghum can substitute for corn as a full season crop and replace soybeans in double cropping systems with wheat in the southeastern United States. Relatively few studies have been conducted to measure the response of grain sorghum to tillage, weed control method, and row spacing. These experiments were designed to determine the effects of weed control method and row spacing on no-till planted grain sorghum (Sorghum bicolor L. Moench G1516-BR) after wheat (Triticum aestivum L. Coker 68–15) and crimson clover (Trifolium incarnatum L. Bigbee) grown for winter forage in comparison to sorghum planted on a conventionally prepared seedbed. The experiment included 45, 60, and 90 cm row spacings and three weed control regimes: none, mechanical, and chemical. Grain sorghum planted no-till in crimson clover or wheat sod yielded considerably more grain than conventionally planted sorghum. Grain sorghum produced significantly higher yields in 45-cm rows than in 60-and 90-cm row spacings with all three planting methods. Effects of chemical weed control on weed population with all tillage methods and on grain yield with conventional tillage were significant. There were no significant differences in grain protein content due to row spacing or weed control method.     

Genotypical differences among graminaceous species in release of phytosiderophores and uptake of iron phytosiderophores

Graminaceous species can enhance iron (Fe) acquisition from sparingly soluble inorganic Fe(III) compounds by release of phytosiderophores (PS) which mobilize Fe(III) by chelation. In most graminaceous species Fe deficiency increases the rate of PS release from roots by a factor of 10–20, but in some species, for example sorghum, this increase is much less. The chemical nature of PS can differ between species and even cultivars.The various PS are similarly effective as the microbial siderophore Desferal (ferrioxamine B methane sulfonate) in mobilizing Fe(III) from a calcareous soil. Under the same conditions the synthetic chelator DTPA (diaethylenetriamine pentaacetic acid) is ineffective.The rate of Fe(III)PS uptake by roots of graminaceous species increases by a factor of about 5 under Fe deficiency. In contrast, uptake of Fe from both synthetic and microbial Fe(III) chelates is much lower and not affected by the Fe nutritional status of the plants. This indicates that in graminaceous species under Fe deficiency a specific uptake system for FePS is activated. In contrast, the specific uptake system for FePS is absent in dicots. In a given graminaceous species the uptake rates of the various FePS are similar, but vary between species by a factor of upto 3. In sorghum, despite the low rate of PS release, the rate of FePS uptake is particularly high.The results indicate that release of PS and subsequent uptake of FePS are under different genetic control. The high susceptibility of sorghum to Fe deficiency (lime-chlorosis) is most probably caused by low rates of PS release in the early seedling stage. Therefore in sorghum, and presumably other graminaceous species also, an increase in resistance to lime chlorosis could be best achieved by breeding for cultivars with high rates of PS release. In corresponding screening procedures attention should be paid to the effects of iron nutritional status and daytime on PS release as well as on rapid microbial degradation of PS.     

盐诱导脯氨酸累积过程中亚胺环己酮的抑制作用

微生物中控制脯氨酸合成的渗透调节基因(osm基因)的转移成功及其抗渗透胁迫能力的提高(Csonka 1980,1981,Le Rudulier和Valentine 1981),启发科学家们把注意力投向高等植物,特别是有经济价值的作物(Bodnar等1989,Nelson等1988,1989,Sanada等1989,Higgins等1987)。采用蛋白质合成抑制剂亚胺环     

Role of cell wall of groundnut roots in solubilizing sparingly soluble phosphorus in soil

Groundnut showed a superior ability to take up P from a soil with low P fertility compared with sorghum and soybean. This ability was not related to its better root development or production of root exudates capable of solubilizing iron-and aluminum-bound P. In efforts to determine the role of roots per se, we found that root cell walls from groundnut showed a higher P-solubilizing activity than those from soybean or sorghum. This finding corresponds well with observations in field and pot experiments using a soil with low P availability. The reaction site of P-solubilizing activity is stable against heating and enzyme digestion by cellulase and pectinase. This is probably the first evidence to demonstrate that cell walls of plant roots are involved in P-solubilizing activity. ei]Section editor: H Marschner (deceased 21 September 1996)     

Interactions between panicle size, insect density, and environment for genotypic resistance in sorghum to head bug,Calocoris angustatus

Studies were undertaken on interactions between panicle size, insect density, host plant, and the environment for sorghum head bug,Calocoris angustatus Lethiery on five sorghum genotypes in terms of bug population increase, grain damage and loss in grain mass across four panicle sizes (5, 10 or 20 branches/panicle and whole panicle), and three infestation levels (5, 10 and 15 pairs of bugs/panicle). Head bug numbers increased and grain damage decreased with an increase in panicle size in the head bug susceptible cultivars, CSH 1 and CSH 5. However, the increase in bug numbers or decrease in grain damage was not significant in head bug resistant genotypes, IS 17610 and IS 17645. Head bug numbers increased with an increase in infestation level in CSH 1 and CSH 5, however, such an increase was not substantial in IS 17610 and IS 17645. Grain damage was significantly lower in IS 17610 and IS 17645 compared with CSH 1 and CSH 5 across infestation levels. Head bug population increased at a greater rate during the rainy season compared with the dry season. Panicle size and infestation levels accounted for greater variation in grain damage and percentage loss in grain mass during the rainy season than in the dry season. To identify reliable sources of resistance to insects, it is important to study insect host plant-interactions across panicle sizes (levels of food availability), infestation levels and seasons.     

Spatial distribution of root activity and nitrogen fixation in sorghum/pigeonpea intercropping on an Indian Alfisol

A medium-duration pigeonpea cultivar (ICP 1–6) and a hybrid sorghum (CSH 5) were grown on a shallow Alfisol in monocropping and intercropping systems. Using a monolith method, spatial distribution of nodulation, acetylene reduction activity (ARA) and root respiration were measured.The number, mass and ARA of nodules decreased exponentially with distance from the plant base except at the late reproductive stage. Nodulation and ARA tended to be higher in the intercrop than in the monocrop.Respiration rate of roots increased with distance from the plant base and reached a maximum value at about 20–30 cm. The rate was higher in pigeonpea than in sorghum and also higher in intercrop than in monocrop.This study suggests that pigeonpea roots are physiologically more active than sorghum roots, implying that pigeonpea may become a strong competitor for nutrients in the soil when intercropped. The nitrogen-fixing ability of pigeonpea may be enhanced by intercropping because the sorghum rapidly absorbed inorganic N which would otherwise inhibit N₂ fixation.