摘要:

Maintenance of leaf water potential (ΨL) during periods of water stress may constitute an important drought-avoiding response. The identification of genotypic variation for this characteristic is, however, made difficult by the fact that comparative values forΨLmust be measured within an environment that changes over the period of time required for a number of measurements. In the course of two field experiments, a number of cultivars were allowed to experience water deficit during early pod fill. During this period,ΨLwas measured for each cultivar on a number of days. The genotypicΨLresponse was expressed on a daily basis as a residual difference from a reference value which was calculated from trends inΨLobserved during each daily measurement period. An average value of this residual over the entire stress period was then determined for each cultivar. The separation of variation inΨL, observed over the stress period, into genotypic and non-genotypic components is discussed and the significance of the genotypic variation is examined. Significant variation inΨLresiduals exists among soybean cultivars under the conditions of this experiment. Such variation is not large, however, with a maximum range of about 0,075 MPa from reference values. Much of this variation was associated with cultivar maturity as earlier varieties gave lowerΨLvalues than did later ones, due possibly to their more advanced growth stage at the time of measurement. Some variation within maturity group was also apparent. Evidence of an association betweenΨLresidual and dryland yield (R2= 0,47) was apparent among the later cultivars in these experiments.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634262

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

Die akkumulasie van vrywater in sekere gronde in die Noordwestelike Oranje-Vrystaat word geassosieer met verskillende tipes stadig-deurlaatbare lae (keerlae). Voorlopige ondersoeke het aangetoon dat die langtermyn-storing van water verskil tussen twee tipes keerlaag, naamlik 'n kleilaag en 'n harde plintiese laag. Kapillêre styging vanaf vrywatervlakke varieer met die tipe keerlaag en ook die diepte van die watervlak. Hierdie verskynsel kan 'n beduidende invloed op die hoeveelheid water wat vir plante in verskillende lokaliteite beskikbaar is, hê. Die moontlikheid dat bykomende plantvoedingstowwe uit die vrywater béskikbaar gestel kan word is bevestig deur analise van die grondwater vir nitraat. Inligting dui daarop dat die grondwater treaties van aard is.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634263

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

The development of the physiological disorder of cotton known as‘rooidood’,‘red leaf disorder’or‘potassium deficiency syndrome’has not yet been explained. Several stress conditions have been associated with this disorder, including low N levels in leaves, low K levels in leaves and soils, high water table, soil compaction, salt accumulation in soil, wilting disorders, windy conditions and large boll loads. The plant's mechanism to avoid carbohydrate starvation in case of untimely stomatal closure, which is dropping of squares and young bolls, cannot function if only large developing bolls are present late in the season. The red leaf disorder may be the result of an alternative mechanism to avoid starvation of inabscisible bolls, to the detriment of assimilates and nutrients of unproductive leaves. All of the mentioned stress conditions associated with the disorder can cause stomatal closure. A large boll load or sink should aggravate the photosynthate shortage of the plant under any such stress. The unmasking of anthocyanin in leaves due to chlorophyll breakdown during the premature senescing process, following stomatal closure, seems to be responsible for the characteristic red colour.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634264

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

The inheritance of drought resistance and agronomic characteristics of field-grown sorghum plants was determined. High heritabilities were recorded for each characteristic. The genetic differences of percentage moisture loss were due to genes exhibiting incomplete dominance. The agronomic characteristics of plant height, peduncle length, days to 50% flowering and yield potential all provided evidence of dominant genetic variation. A few parental inbred lines that could be used to improve drought resistance of commercial hybrids have been identified. Results indicated that the percentage moisture loss of excised leaves of mature plants could be used as a selection criterion for drought resistance in sorghum.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634265

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor

摘要:

The use of empirical relationships for the calculation of the energy and aerodynamic components of the Penman-Monteith equation were tested against measured data. Accurate estimates of maximum total evaporation, Em, from a wheat crop were obtained. The empirical equation utilizes measured or estimated total radiation flux density, St, in the energy component, plus evaporation from a screen Pichéatmometer to account for aerodynamic influences. The agreement of estimated Em versus lysimetrically measured Em was good. The high index of agreement of 0,98 and a low mean absolute difference of 0,51 mm over the daylight period were obtained with St measured. When St was estimated, using an appropriate formula, these statistics were 0,98 and 0,57 mm, respectively.

ISSN:0257-1862    

DOI:10.1080/02571862.1988.10634266

出版商:Taylor&Francis Group    

年代:1988

数据来源: Taylor