摘要:

Thirteen winter and intermediate type bread wheat cultivars were evaluated under dryland conditions over a four year period from 1991 to 1994 and over 120 environments in the Free State province of South Africa. The Additive Main Effects and Multiplicative Interaction (AMMI) statistical model was used to describe genotype-environment (G × E) interaction of yield performance under dryland conditions. In all three relatively homogeneous production regions, viz. Western, Central and Eastern Free State, the AMMI model identified distinct patterns of adaptation. The hybrids and long growth period pureline cultivars generally had superior adaptation to high yield potential conditions, while the short and medium growth period pureline cultivars were better adapted to lower yield potential conditions. The AMMI model indicates that it can effectively summarise patterns of adaptation of winter wheat genotypes and similarities of Free State environments, as well as offer a valuable prediction assessment.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634877

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Thirteen winter and intermediate type bread wheat cultivars were evaluated for yield stability under dryland conditions over a four year period from 1991 to 1994 and over a total of 120 environments in the Western, Central and Eastern Free State wheat producing regions of South Africa. The following statistical analyses were conducted and procedures followed to determine yield stability: (i) Shukla's procedure of stability variance(*2j); (ii) Lin and Binns cultivar performance measure (Pi); (iii) Finlay and Wilkenson's regression analysis and coefficient (b); (iv) Eberhart and Russel's deviation from regression (S2d); (v) Wricke's ecovalence (W1); (vi) AMMI model. Since the AMMI model does not make provision for a quantitative stability measure, such a measure was developed to rank genotypes. Total correspondence for significance of Spearman's rank correlation coefficients for the different analysis procedures was noted over the three production regions. No significant rank correlation coefficients were found in the pairwise comparisons of both Lin and Binns' and Finlay and Wilkenson's procedures with the other procedures, nor in the comparison between the two mentioned procedures. This indicates that the Lin and Binns procedure, as well as the Finlay and Wilkenson procedure, differ significantly from the other procedures in stability determination and definition, and due to noted deficiencies are consequently not recommended for use. From the study it would appear that if a single method of describing the stability of a genotype had to be selected, the proposed AMMI Stability Value (ASV) AMMI model would be the most appropriate. Certain cultivars showed similar stability over the three regions, while others varied considerably over the three regions.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634878

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Unbranched rooted layers of the rootstock Mailing 9 (M.9 clone Nie 29) ≈600 mm long were treated twice in autumn (4 and 13 October 1995) in the stoolbed as follows: a) non-treated control; b) the distal 300 mm of the shoot was painted with an aqueous solution of TIBA [250 mg 1−12,3,5-triiodo-benzoic acid with 2 ml l−1Tensospray wetting agent (100 g l−1alkyl-aryl-polyethyleneglycol)]; c) the proximal ®300 mm of the shoot was painted with an aqueous solution of Promalin® (3000 mg 1−1N-(phenylmethyl)-1H-purine 6-amine and 3000 mg 1−1gibberellins A4+A7without a wetting agent); d) the above TIBA and Promalin treatments combined on the same shoot. Twenty rooted stoolshoots per treatment were forced on 20 October 1995 (autumn), 5 December 1995 (mid-winter), and 21 February 1996 (late winter). The growth rates of the terminal bud, an upper lateral bud (≈200 mm from the apex) and a lower lateral bud (≈400 mm from the apex) were observed. Twenty additional rooted shoots per treatment were allowed to growin situ.Budburst relative to bud position was regularly recorded until no further change was observed. Two months later, length and position of the new shoots was recorded. The application of TIBA to the distal shoot half reduced the ability of the distal buds to establish dominance. The application of Promalin to the proximal lateral buds increased the growth rate sufficiently to overcome the distal inhibitions associated with acrotony, and burst simultaneously with the terminal bud. Promalin increased the basitonic branching from proximal buds. The data suggest the hormonal control of the correlative phenomena that determine tree architecture.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634879

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Field experiments were conducted during two growing seasons to determine the effect of different common thorn-apple (Datura stramoniumL.) densities on seed germination. The study provided information on the implications of weed and weed seed infestation, where no weed control was applied. Maize (Zea maysL.) was planted in 2.1 m rows at a plant population of 16 000 plants ha−1.D. stramonium wasplanted at five densities in association with maize. Harvested weed seeds were subjected to a series of germination tests. During both seasons the germination and vigour of the produced weed seeds declined with increased weed-crop interference. The data contribute towards timely, more effective and environmentally friendly weed control.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634880

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Soil Water Balance (SWB) generic crop growth and irrigation scheduling model was used to simulate the crop growth and soil water balance of sunflower (Helianthus annuusL. c v. CAR 1199 and SO 306) grown at Rietrivier. The objectives were to determine crop specific growth parameters for sunflower and to calibrate and validate the SWB model so that irrigation of this crop can be scheduled mechanistically and accurately. A database of growth parameters for sunflower was generated using international literature data or by estimation and included in SWB. Detailed weather, soil and irrigation data from the field trial were then used to calibrate and validate the crop growth and soil water balance subroutines of the model. Simulations of crop growth and soil water deficit to field capacity were inside, or marginally outside the reliability criteria imposed. Deficit irrigation strategies can be simulated reasonably well with the mechanistic SWB crop growth model. The performance of SWB should, however, be tested with independent data sets and for a wider range of yields, cultivars and ecotopes.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634881

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Since 1996, several incidents of poor weed control regarding little seeded canary grass (Phalaris minorRetz.) in wheat (Triticum aestivumL.) production have been reported from the Western Cape. Little seeded canary grass showed indications of resistance towards ACC-ase inhibitors. Seed from these suspected resistant biotypes as well as seed from a susceptible biotype were collected from mature surviving plants and transported to the Small Grain Institute, Bethlehem where herbicide resistance studies were done. Herbicides used during the study were diclofop-methyl, clodinafop-propargyl and iodosulfuron. Both diclofop-methyl and clodinafop-propargyl are ACC-ase inhibitors and iodosulfuron is an ALS-inhibitor. Significant differences in the degree of control were found between the susceptible and four resistant biotypes when treated with diclofop-methyl and clodinafop-propargyl. When treated with diclofop-methyl, the LD50values for the resistant (PMR 1, PMR 2, PMR 3 and PMR 4) biotypes were 594, 700, 225 and 2673 g a.i.ha−1respectively, whereas the LD50value for the susceptible biotype was 184.4 g a.i.ha−1. The LD50values for the PMR 1, PMR 2, PMR 3 and PMR 4 biotypes treated with clodinafop-propargyl, were 79, 94, 29 and 280 g a.i.ha−1respectively, whereas the LD50value for the susceptible biotype was 24 g a.i.ha−1. No significant differences could be found between the susceptible and resistant biotypes when treated with iodosulfuron. The LD50values for the susceptible and resistant biotypes varied between 27.4 and 29.2 g a.i.ha−1. This is, therefore, the first report confirmingP. minorresistance to diclofopmethyl and clodinafop-propargyl treatments in the Republic of South Africa.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634882

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The nitrogen advantage of legumes in crop rotation systems is well known, but the nitrogen advantage from legumes to associated crops in an intercropping system is unclear. The objective of this study was to determine whether plant-available nitrogen is released by cowpea and soybean during the growing season, since this could mean a saving in nitrogen fertilizer for an associated crop in an intercropping system. Nitrate nitrogen levels were monitored monthly throughout two growing seasons on cowpea, soybean and maize plots at two localities. There was no evidence of nitrogen enrichment of soil by the legumes in the early growing stages, but nitrogen was released into the soil when the legumes reached maturity, about four months after planting. The nitrogen enrichment of the soil occurred only within the legume rows, since no differences in nitrogen levels were found between the rows. This suggests that the mechanism of nitrogen enrichment of soil from these legumes is the rapid mineralization of nitrogen from roots and/or nodules when they reach maturity. It is, therefore, unlikely that legumes can provide a nitrogen advantage to associated crops within an intercropping system in the same season.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634883

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The quality of South African sunflower oil cake varies and often has an unacceptably low protein and high crude fibre content. Poor hullability of the seed is generally regarded as the primary cause thereof. This study examines the contribution of cultivar and environment to the variation in yield, physical seed traits and hullability. Seed of five cultivars produced at six environments was analysed: Grain yield and all the seed traits were affected by cultivar, environment and a relatively small cultivar × environment, interaction. Environmental effects caused the most variation for yield, hectolitre mass, hull content and the amount of fines produced, while the thousand seed weight and hullability were mainly affected by cultivar. The cultivar PAN 7392 had a high and stable hullability over environments indicating that breeding for such seed traits is possible. Correlation coefficients between hullability and the easily measurable seed traits were poor. Both the negative relationship between hectolitre mass and hullability and the positive relationship between the hectolitre mass and amount of fine material produced, indicate that seed with low hectolitre mass should be preferred for maximising the chance of obtaining seed of acceptable processing quality.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634884

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The processing quality of sunflower seed is determined by its oil yield, oil cake yield and oil cake composition. Quality of the oil cake is determined by its protein and crude fibre content. Seed composition is affected by both cultivar and environment. This study examines the contribution of cultivar and environment to the variation of seed oil, protein and crude fibre content, and its relation to the potential oil yield and potential quality and yield of the oil cake. Seed of five cultivars produced at six environments was analysed. Oil, protein and crude fibre content, as well as the potential oil yield, were affected more by environmental than by genetic effects. Environment was also the main contributor to variation in protein content of the potential oil cake. Crude fibre content of the potential oil cake was affected slightly more by environment than cultivar. Protein content of the potential oil cake declined with increased seed oil content. The crude fibre content of the potential oil cake of cultivar PAN 7392 was high despite high hullability, indicating the need for fibre analyses to support hullability analyses.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634885

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Grey leaf spot (GLS) caused byCercospora zeae-maydisTehon and Daniels has become the most important foliar disease of maize in South Africa. Crop rotation has been applied successfully to control or reduce the incidence and severity of plant diseases in general. GLS severity in maize monoculture and maize rotated with soybeans was monitored over four growing seasons. To reduce interplot effects experimental plots were surrounded by buffer rows of a resistant maize cultivar which was sprayed with fungicides every two weeks. Percentage GLS severity was visually assessed at fortnightly intervals. No significant differences in grey leaf spot severity were found between maize grown in monoculture or when rotated with soybeans. This result may be attributed to the ability of grey leaf spot spores to survive for two years in maize debris on the soil surface. It appears, therefore, that short term crop rotation will not control the disease under epidemic conditions.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634886

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor