South African Journal of Plant and Soil

Microsatellite characterisation of South African Puccinia striiformis races

2016-10-11T14:17:59+00:00

Since the first appearance of wheat stripe rust in 1996 in South Africa, four Puccinia striiformis races have been described. The first detected race, 6E16A−, was proposed to be a foreign introduction from Central or Western Asia that subsequently gained additional virulence through step-wise mutations. Simple sequence repeat markers were used to determine the genetic relationships between the four races, as well as a P. striiformis isolate collected from wild rye and two Kenyan isolates. A single isolate of P. striiformoides collected from Dactylis glomerata was included as an out-group. While the genetic similarity between P. striiformoides and the two Kenyan P. striiformis isolates was low, both shared only 48% genetic similarity with the South African isolates. In contrast, the South African P. striiformis isolates shared at least 74% genetic similarity with each other, with 6E16A−, 6E22A− and 7E22A− being the most similar. A minimum spanning network analysis confirmed this close relationship with several hypothetical intermediates occurring between individual races. This suggests that the South African P. striiformis population is clonal. However, the fact that P. striiformis was introduced into the country suggests that further incursions of more aggressive isolates could occur, which could threaten wheat production in the country.

Keywords: South Africa, SSRs, stripe rust, wheat

Wetland hydrology indicators of Maluti Mountains wetlands in Lesotho

2016-10-11T14:18:01+00:00

Hydric soil morphological features are generally accepted to be reliable indicators of wetland hydrology. The relationship between soil water saturation and soil morphological indices is evaluated in this study from bi-weekly water level data taken over a period of two years. The hydrological behaviour of the Bokong wetlands is described by recession in hydrographs during the low rainfall season. However, the fens and hillslope seeps (PW08, PW19, PW21, PW24 and PW32) indicate spikes under the low rainfall period, associated with subsurface flow from the surrounding catchments and streams. Wetlands PW06, PW07 and PW27 were bogs and had soil organic carbon higher than 12%. The falling water levels in the bogs suggest that the wetlands are mainly recharged by precipitation and runoff. The water level resides within the 0–500 mm depth for 80% of the monitoring time. Strong correlations are observed between soil morphological indices and cumulative water saturation. The coefficients of determination (r 2) for depth to gley matrix, depth to chroma 3 or 4, and profile darkening index were 0.74, 0.77 and 0.88, respectively. These hydric indicators therefore can be used to determine wetland hydrology. Histisols, histic epipedons, umbric surfaces, thick dark surfaces and loamy gleyed matrix occur.

Keywords: cumulative saturation, hydric soils indicators, morphological indices, wetland hydrology

Identification and molecular characterisation of Colletotrichum species from avocado, citrus and pawpaw in Ghana

2016-10-11T14:18:02+00:00

Owing to previous identifications based solely on morphological characteristics, the identity of the causal agents of anthracnose disease of pawpaw and avocado in Ghana is in doubt. In addition, the pathogen has not been identified previously on citrus. In this study, isolates of the pathogen were obtained from anthracnose lesions on avocado and pawpaw, and atypical anthracnose lesions on citrus. The isolates were identified using PCR with speciesspecific primers, complemented by phylogenetic analysis of nucleotide sequences of the internal transcribed spacer region and partial glyceraldehyde-3-phosphate dehydrogenase gene. The pathogenicity of the isolated fungi was determined on detached matured fruits. All isolates, including those isolated from citrus, were identified as Colletotrichum gloeosporioides from the expected 480 bp PCR products amplified by PCR. The phylogenetic analysis showed that isolates from avocado and pawpaw were C. siamense, rather than C. gloeosporioides, whereas isolates from citrus were C. gloeosporioides sensu stricto. The pathogens were able to induce disease only on wounded mature fruits.

Keywords: Colletotrichum gloeosporioides sensu stricto, Colletotrichum siamense, glyceraldehyde-3-phosphate dehydrogenase, internal transcribed spacer region

Crop rotation and tillage system effects on reducing ryegrass occurrence in spring wheat

2016-10-11T14:18:04+00:00

Under the Mediterranean climatic conditions of the Western Cape province, the Swartland region is intensively cropped, producing spring wheat (Triticum aestivum L.), but due to ryegrass competition, yield is reduced. In addition, ryegrass has developed resistance to herbicides. This necessitates the use of integrated weed management practices for suppressing ryegrass in wheat fields. The objectives were to quantify and qualify the impact of crop rotation and tillage systems used in combination with reduced herbicide input and to determine whether these could reduce ryegrass population numbers. Analyses of variance of data were used to determine crop rotation × tillage system response in field and shade-netting experiments. Wheat monoculture, in both tillage systems, was associated with the highest ryegrass population increase in both years. The results of both the field and shade-netting experiments showed that there was no significant difference between minimum-tillage and no-tillage in reducing ryegrass numbers. Results obtained from the shade-netting experiment indicated that the three crop-rotation treatments under minimum-tillage differed significantly from the control. In the field wheat–medic–wheat–medic rotations under no-tillage out-performed all other rotations, followed by wheat–lupin–wheat–canola under minimumtillage. It is essential to use competitive crop sequences that decrease particular weed population numbers.

Keywords: crop rotation, ryegrass reduction, ryegrass seedling emergence, tillage system

Agronomic performance of early segregating generations of rice under salt stress in Niger

2016-10-11T14:18:05+00:00

Salinity is a major abiotic constraint that retrains rice production worldwide. The development and release of rice cultivars with improved performance in saline environments is essential to fight against this scourge. Hence this study was carried out to evaluate segregating populations of rice in Niger where salinity is a major constraint. Thus 120 F3 families derived from a diallel cross of four parents were evaluated in salt-affected farmer’s fields at two sites. The experimental design was an alpha lattice 25*5 with three replications and two sites. Data on the cycle, height, tiller number, panicle number, panicle weight, grain weight, and yield were recorded. Data were analysed using SAS 9.2 and least significant difference was used for means separation. Yield potential under salt stress varied significantly among F3 families ranging from 2.52 to 4.17 t ha⁻¹. Correlation analysis among traits showed that yield was significantly and positively associated with height, tiller and panicle number, and panicle weight. The 20 best-performing families with a high selection index were selected for advancement for farmer’s adoption.

Keywords: rice, F3 families, Niger, performance, salinity

Inheritance of resistance to Ug99 stem rust pathogen in selected barley lines

2016-10-11T14:18:06+00:00

Stem rust (Puccinia graminis tritici) race Ug99 is a devastating disease of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). Barley is the world’s fourth most important cereal crop after wheat, maize (Zea mays L.) and rice (Oryza sativa L.). The seedlings of F2 populations were inoculated 7–10 d after planting and when the first leaf was fully emerged (Feekes stage 1). The observed resistant (R):susceptible (S) ratio f the F2 populations HKBL-1385-13 × 08-UT-86 (χ² _0.05 = 0.480, P ≥ 0.488), HKBL-1385-13 × 09-N2-19 (χ² _0.05 = 0.641, P ≥ 0.424), ND2649 × 09-AB-78 (χ² _0.05 = 1.05, P ≥ 0.309) and ND25882 × 09-AB-78 (χ² _0.05 = 3.599, P ≥ 0.058) exhibited Mendelian segregation of 3R:1S suggesting that the resistance is conferred by major genes. In addition, F2 populations derived from the crosses Karne × 09-N2-19 (χ² _0.05 = 1.343, P ≥ 0.246), Nguzo × 09-AB-78 (χ² _0.05 = 0.429, P ≥ 0.512), ND26249 × 09-N2-52 (χ² _0.05 = 2.576, P ≥ 0.111) and ND25882 × 09-AB-78 (χ² _0.05 = 0.980, P ≥ 0.322) conformed to a phenotypic ratio of 9:7 indicating that there are genes modifying the resistance to Ug99. The results of this study suggest that there are valuable major genes for stem rust resistance that could be used to improve susceptible barley and wheat germplasm.

Keywords: barley, Mendelian, stem rust, Ug99

Sorghum production systems and constraints, and coping strategies under drought-prone agro-ecologies of Ethiopia

2016-10-11T14:18:07+00:00

Sorghum is one of the most important cereal crops worldwide after wheat, rice, maize and barley. Examining the present socio-economic conditions of sorghum-producing farmers in different agro-ecologies in Ethiopia is of importance for the design of improvement strategies. The objectives of this study were to evaluate the sorghum production system and patterns, major production constraints and related coping strategies in north-eastern Ethiopia. Twelve sorghum-growing villages in the North Welo, South Welo and Waghemra districts were surveyed. Descriptive statistics and a generalised additive model were used for data analysis. Constraints affecting the productivity of sorghum include moisture stress, insect pests, striga, farmland shortage, poor soil fertility, diseases, and low-yielding local cultivars. Among the constraints, drought at the grain-filling stage was identified as the most important production problem in the target region. The productivity of sorghum was also hindered by the use of local drought-tolerant but low-yielding landraces, because farmers had been forced to abandon high-yielding and late-maturing landrace cultivars because of the frequent occurrence of drought. To enhance sorghum productivity, farmers’ knowledge and practices, and production constraints need to be integrated from the initial stages of breeding and technology development.

Keywords: generalised additive model, moisture stress, participatory rural appraisal, production constraint, sorghum

Effects of rooting media on root growth and morphology of Brassica rapa seedlings

2016-10-11T14:18:09+00:00

Rooting media used in current root phenotyping studies can have substantial effect. In this study, the effects of three different nutrient conducting papers (Black construction paper, Anchor blue germination paper and Kimpak paper) and soil-filled boxes on root growth and root system architecture (RSA) of Brassica rapa (cultivars ‘R500’ and ‘IMB211’) were investigated. Seedlings of the two B. rapa genotypes were supplied with nutrients on the nutrient conducting papers and in the soil-filled boxes. The papers and soil-filled boxes were fixed to flatbed scanners and two-dimensional images of roots were periodically taken and analysed. Root media effects on shoot and root biomass and on topological indices (TI) were observed. For example, root branching was more pronounced on the construction paper. Mean TI of 0.82 and 0.93, recorded for R500 and IMB211, respectively, on the construction paper indicated that substrates affect the herringbone pattern of brassica roots. Whilst it was indicated that different results could be obtained for the same RSA when different germination papers are used, the results showed that Anchor blue germination paper is an ideal proxy for soil in phenotyping seedlings for RSA traits and root growth.

Keywords: germination paper, phenotyping, rooting media, root system architecture, topological index

Sensitivity of selected dry bean (Phaseolus vulgaris L.) cultivars to mesotrione in a simulated carry-over trial

2016-10-11T14:18:10+00:00

Mesotrione is used to control annual broadleaf weeds and grasses in maize, with waiting periods up to 24 months recommended prior to planting sensitive crops. The objectives of this study were to determine if selected dry bean cultivars exhibited differences in sensitivity to mesotrione, and the lowest concentration that would cause significant damage. A pot trial was carried out using two small white canning bean and six red speckled bean cultivars. Mesotrione was applied at 51.2, 1.6, 5 × 10⁻², 1.5 × 10⁻³, 4.9 × 10⁻⁴, 1.5 × 10⁻⁶, 4.8 × 10⁻⁸ and 0 μg kg⁻¹ soil. Numbers of days to emergence, number of emerged seedlings as well as phytotoxicity symptoms were monitored, with plant height and mass determined at harvest. Symptoms varied from bleaching and necrosis at the higher rates, through to malformed and crinkled leaves. Highly significant effects due to both cultivar and mesotrione rate were noted on plant height, as well as a highly significant interaction effect on dry mass. The 270-day waiting period prior to planting dry beans appears to be sufficient to avoid damage to the cultivars tested on the soil type used. Although cultivar differences in sensitivity were noted, no distinct groups could be identified.

Keywords: cultivars, dry beans, mesotrione, phytotoxicity, sensitivity

Evaluation of the effects of phosphorus and nitrogen source on aerial and subsoil parameters of maize (Zea mays L.) during early growth and development

2016-10-11T14:18:12+00:00

Understanding the nutrient requirements of maize is especially important during early vegetative growth and development, particularly when produced on highly weathered soils with low organic matter contents. Therefore, the growth response of maize to different nitrogen (N) sources viz. limestone ammonium nitrate and urea, phosphorus (P) sources viz. monoammonium phosphate, nitrophosphate and ammonium polyphosphate, as well as P application levels viz. 0, 10, 20, 30 and 40 kg ha⁻¹ during early growth were evaluated. In pot trials with a sandy loam topsoil, aerial and subsoil plant parameters were measured to evaluate the effect of treatment and treatment combinations of P and N fertilisers on the vegetative growth and development of maize during the first five weeks after emergence. Plants treated with limestone ammonium nitrate had significantly greater plant parameter measurements compared with urea, primarily ascribed to immediate availability after application in addition to ease of uptake. Monoammonium phosphate and nitrophosphate (orthophosphate sources) yielded significantly greater aerial measurements compared with ammonium polyphosphate (polyphosphate source). Differences in subsoil plant parameter results for P source were not that clear. Aerial and subsoil plant parameter measurements were overall significantly greater with P applied at 40 kg ha⁻¹ than the majority of lesser application rates.

Keywords: nitrogen source, orthophosphate, plant growth parameters, polyphosphate