摘要:

Aluminium toxicity was investigated by analyzing the mineral nutrition and water-use characteristics of hydroponically-grown plants differing in tolerance to Al when subjected to Al (0, 20, 40, 80 μM: pH 4.5) for 28 days. Both lines reacted to Al by increasing their water-use. The Al-tolerant plants were, however, able to control the Al-stimulated water fluxes and progressive increases in water-use (increasing Al) were limited to the Al-sensitive material. Although Al was not generally transported into the foliage, Al treatments nevertheless elicited changes in the composition of the leaves including apparently opposite effects on the Ca, K and P levels found in Al- tolerant and Al-sensitive plants. Analysis of these differences revealed that leaf Ca concentrations were positively related to water-use while leaf K was antagonistically linked to Ca and thus inversely related to the Al- stimulated changes in the plants' water-use. Differences in K nutrition centred around P transport and fluctuations in leaf P paralleled the Al-stimulated changes in foliar K concentrations. These findings are used to develop a theory of root-to-shoot communication in Al-stressed plants which encompasses water fluxes and ion transport processes.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634837

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

TheLr19translocation is preferentially transmitted to the progeny of a heterozygote due to the actions of at least two genes,Sd1andSd2(new designation). However, onlySd2occurs in the recombinant,Lr19-149, and often causes self-elimination of the recombined translocated segment in heterozygotes. The degree of segregation distortion is determined by the interaction of theSdgenes with polygenes (responder genes) on various wheat chromosomes. In this study suspected responder alleles derived from ‘Inia 66’ or ‘Indis’ (chromosomes 2A, 2B, 3B, 5B, 5D and 6D) appeared mostly to be partially dominant to overdominant over the ‘Chinese Spring’ derived alleles. A specific allele may not necessarily hafe-tfoe same effect (suppression or enhancement) in different genetic backgrounds. Responder genes may not fully compensate for the absence of a homologue in a hemizygote which may then produce effects quite different from those of the homo- and heterozygotes.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634838

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Yield losses due to high temperatures in the wheat growing season is a serious problem in South Africa. The aim of this study was to determine how the expression of general combining ability (GCA) and specific combining ability (SCA) was influenced by high temperatures in five commercial spring wheats. A full diallel cross was made with five spring wheat cultivars. One set of parents and their F1 hybrid progenies were grown under high temperatures and a second set under control temperatures. Additive gene action was predominant for all characteristics measured at both temperature levels. Additive gene action was significantly lower at the higher temperature conditions for most characteristics. Parents with the highest GCA effects at one set of temperatures tended to have the highest GCA effects for the other temperature level as well. SCA effects were expressed significantly different at the higher temperatures. High SCA effects for a characteristic at one temperature level were often paralleled by low or negative SCA effects at the other temperature level. This indicated that specific hybrid combinations selected in an optimal environment would probably not perform the same at high temperature conditions.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634839

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The leaf surface morphology of C.benghalensisand the ultra structura I changes in C.benghalensisleaves caused by herbicide treatments in combination with adjuvants were studied with electron microscopes. The study indicated u It ra structural changes in treated leaves. All treatments caused changes in infrastructure in parenchyma cells. Three days after treatment, thylakoids in parenchyma cells were swollen and disrupted chloroplast envelopes were visible. The chloroplasts appeered swollen and were spherical in shape and also lacked starch grains.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634840

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Two integrated control strategies were developed for areas where wattle infestations could be utilized. Costing analyses were determined for initial control and four follow-up control operations using chemical control and fire. Efficacy of all treatments was high. Costs were significantly reduced during follow-up control operations. Rehabilitation of the cleared areas with pasture species stabilized the top soil and increased the carrying capacity of the land. The pastures could be maintained or allowed to revert to neighbouring veld (grassland) species, depending on the aims of the land manager. The financial returns from conversion of wattle infestations to pastures required 1 or 7 years utilization (grazing) to cover the costs of control, depending on the production system used. Control costs of these trials were compared with contract-based costs at the Kouga Work for Water project in the Eastern Cape.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634841

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Four integrated control strategies were developed for wattle that could not be removed for utilization. In the first two strategies, a combination of mechanical and/or chemical control methods either reduced the wood biomassin situ(fell, stack and burn) or retained the wood biomass above the soil surface (control of standing trees). Follow-up control involved a combination of chemical control and burning high fuel loads of sown pastures species. For the third strategy, dense infestations were contained and prevented from encroaching into neighbouring veld (grasslands). These infestations were controlled once sufficient funds became available, or converted to wood lots and shelter belts. The fourth strategy describes control of dense seedling regeneration promoted by uncontrolled fire, and the calculation of a reserve ‘fire fund’. A customized management plan was developed for a particular property that assigned these six integrated control strategies to infestations in different situations. Prioritizing the infestations allowed the optimum allocation of the available resources within a realistic time span, thereby ensuring sustained progress was made in the reduction of infestations to acceptable levels.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634842

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The gene Cry1Ab derived from the entomopathogenic bacteriumBacillus thuringiensisis currently deployed commercially for control of Pyralid stem borers of maize in the USA. In this study various events of the Bt-gene were evaluated in maize inbred lines and hybrids for leaf feeding resistance to the local stem borersBusseola fuscaandChilo partellus, using artificially infested plants under greenhouse and field conditions. The event MON810 proved superior to all other events tested. C.partelluswas more susceptible thanB. fuscato the same events. Significant maternal effects were observed. Efficacy was not negatively affected by variations in the time of infestation. Hybrids did not respond equally to transformation with the same event, which was attributed to differences in adaptation to adverse environmental conditions.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634843

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Although numerous studies, both phenomenological and mathematical, have related gaseous interchanges at the plant leaf surface and atmospheric interface specifically with regard to drought tolerance, the important role of trichomes and the boundary layer has not been recognized. In this investigation the focus was restricted to the role of the boundary layer along with stomatal geometry and -spacing in determining the diffusional resistance to CO2and H2O in fourNicotiana tabacumL. cultivars of different, but known, drought tolerance. Resistances were expressed both in terms of resistance components on a unit leaf area basis andin terms ofdimensionless quantities. The abaxial leaf surface had the highest trichome frequency, more so in the drought tolerant than in the drought sensitive cultivars, being 9.7% and 6.9% higher than on the adaxial surface for TL33 and CDL28, as opposed to being 21.2% and 26.8% higher for GS46 and Elsoma, respectively. The frequency of the long glandular trichomes of epidermal cells, and consequently also the calculated stomatal index, was significantly (p < 0.01) higher on the adaxial surface of the drought tolerant cultivars. Both the fractional cavity and pore contributions to the overall entry resistance were higher for the drought tolerant cultivars, being 24.1 % (H2O) and 20.6% (CO2) for the stomatal cavity, and 9.5% (H2O) and 7.4% (CO2) for the stomatal pore contributions, respectively. The fractional contribution of the boundary layer was, however, on average 3.4% (H2O) and 6.5% (CO2) higher for the drought sensitive cultivars. From the results presented it is concluded that plant fitness for tolerating drought in this mesophytic crop plant may be maximized not by minimizing water loss or by maximizing the photosynthetic to transpiration ratio, but by maximizing the carbon gaining capacity of the leaf.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634844

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Studies have been conducted in Nigeria on biology ofCicadulinaleafhopper vectors of maize streak virus (MSV), the role of indigenous grasses as reservoirs of virus and vectors, and on incidence and severity of MSV in relation to maize varietal susceptibility/resistance levels.Cicadulinapopulations peak before rains end in the savanna and after the rains in the forest zone. The proportion of viruliferous leafhoppers increases as the season progresses. C.mbilais the predominant vector species; four other species are less common. Off-season survival of MSV and vectors occurs in riverine areas in grasses and in areas with hydromorphic soils where maize is grown during the dry season. However, streak found in many grasses in Nigeria is not readily transmissible to susceptible field maize. Weeds most likely to perpetuate an epidemiologically-competent MSV maize strain areAxonopus compressus(an introduced perennial),Brachiaria lataandSetaria barbata(indigenous annuals). MSV epidemics occur only in years when weather conditions allow vector survival and build-up, and where maize-competent strains are present in grass hosts. MSV disease reduces maize yield, but varieties differ in incidence and severity of disease, and yield loss. Resistant varieties exhibit tolerance—good yield performance when diseased—and lower disease incidence. Low disease incidence is partly due to insect resistance and potential for disease spread is lower on varieties exhibiting this character.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634845

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Short-duration groundnut cultivars were screened under high, medium and low rosette disease pressures and evaluated for rosette disease incidence, presence of groundnut rosette assister virus and other agronomic characteristics. Heritabili- ties of these characteristics and interaction plus variance components across the three disease pressures were calculated. Significant differences among the entries were observed for both agronomical parameters and disease resistance. Broad-based heritabilities for pod and kernel yields under high disease pressure were higher than the values for rosette resistance. It is expected from the results that the genetic improvement for rosette disease resistance will be higher using pod yields as a selection criterion. The interaction components between cultivars and disease pressures were significant, suggesting different responses of the cultivars across the three disease pressures. Yield stability may only be introduced when the cultivars are evaluated under different disease pressures.

ISSN:0257-1862    

DOI:10.1080/02571862.1999.10634846

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor