Diana Marais

Response of tomato (Solanum lycopersicum L.) to nursery inoculation with Trichoderma harzianum and arbuscular mycorrhizal fungi under field conditions

Abstract The effect of nursery inoculation of tomato (Solanum lycopersicum L.) with Trichoderma harzianum and arbuscular mycorrhizal fungi (AMF) Glomus mosseae on fungal root colonization, plant growth, yield and quality of field-grown tomato was investigated. The four treatments included T. harzianum, AMF, T. harzianum+AMF, and uninoculated control. At mid-harvest, 84 days after transplanting, no interactive effect of the fungi on the external mycelium growth was observed. Inoculation with AMF alone or in combination with T. harzianum increased dry shoot weight by 35% and 30%, respectively, during the first season, and by 30% and 21%, respectively, during the second growing season. Trichoderma harzianum increased the percentage of large fruit by 76% in 2008–2009, whereas AMF increased the percentage of extra-large fruit by 44% in 2009–2010. Similarly, AMF increased total soluble solids by 10%. Inoculated tomato seedlings with T. harzianum and/or AMF significantly increased early yield of tomato, by 10%, 65% and 70%, respectively, during 2008–2009, and by 27%, 36% and 37%, respectively during the 2009–2010 growing season. In conclusion, results of the study suggested that T. harzianum and AMF have the potential to improve growth, early yield and fruit quality of field-grown tomato.

Dry matter yield and water use efficiency of five perennial subtropical grasses at four levels of water availability

The effect of four levels of water availability on the yield and water use efficiency (WUE) of five subtropical perennial grasses was evaluated in a small plot trial under a rain shelter. The soil profiles were brought to 100% (W4 = the control), 75% (W3), 50% (W2) and 25% (W1) of field capacity on a weekly basis. Under W4 (control) and W3 conditions, yields did not differ significantly from each other. Where water became less available (W2 and W1), yields were significantly reduced, in comparison with the control (W4). Buffel grass, a drought-tolerant species, produced yields (11.7–20.0t ha−1) under moderate to severe water restriction (W1, W2 and W3), which were comparable with yields obtained with adequate water (W4) for traditionally-irrigated grasses such as couch grass (12.0–15.8t ha−1) and kikuyu (5.6–11.8t ha−1). All five grass species tended to use water more efficiently under moderate to severe water-limiting conditions (W1 and W2) than under control conditions (W4). These results also indicate that traditionally drought-tolerant grass species should not be overlooked when identifying species for use under irrigation.

Economics, yield and ecology : a case study from the South African tomato industry

A clear tomato yield gap exists in southern Africa. Understanding the economic crop production factors is a necessary prelude to any discussion of ecological sustainability. The objective of this study was to evaluate the economic factors that influence the sustainability of open-field tomato production. The authors compared detailed tomato production costs from six international studies to data from the largest commercial tomato producer in South Africa. The Environmental Impact Quotient (EIQ) was used to demonstrate the interactions between economic and agro-ecological constraints. Economic pressures are forcing tomato producers to intensify production, which underscores the need for the continued development of ecologically sustainable tomato production systems. The findings of this study will benefit policy development in support of sustainable food security in the rural areas of southern Africa and beyond.

Predicting seedling emergence of cabbage and onion using vigour tests

Predicting seedling emergence using standard and non-standard germination temperatures, standard accelerated ageing (AA) and saturated salt accelerated ageing (SSAA) tests, were investigated. Germinations were performed at temperatures of 10°, 20°, 20°/30° and 30°C for cabbage (Brassica oleracea var. capitata L.) and 10°, 15°, 20° and 30°C for onion (Allium cepa L.). Seeds were aged using relative humidities of 32% (RH32), 43% (RH43), 75% (RH75) and 100% (RH100). Emergence trials were conducted at a range of temperatures (winter, 15°/25° and 30°C) and growth media. Most SSAA vigour tests were useful in differentiating seed lots based on their physiological stage of deterioration. In the SSAA tests, the seed moisture content remained below 14% and no fungal growth occurred. For cabbage, highly significant correlations were obtained between 10°C and RH32 and all emergence trials. For onions highly significant correlations with emergence percentage were obtained with germinations at 15° and 30°C. Mean germination time (MGT) and germination energy (GE) were valuable in categorising seed lots with moderate vigour levels, however, only GE revealed good correlation with winter emergence trial of onions.

Assessment of gene flow between gossypium hirsutum and G. herbaceum : evidence of unreduced gametes in the diploid progenitor

In the framework of a gene flow assessment, we investigated the natural hybridization rate between Gossypium hirsutum (AADD genome) and G. herbaceum (AA genome). The latter species, a diploid progenitor of G. hirsutum, is spontaneously present in South Africa. Reciprocal crosses were performed without emasculation between G. herbaceum and G. hirsutum. Neither examination of the morphological characteristics nor flow cytometry analysis of the 335 plants resulting from the G. hirsutum × G. herbaceum cross showed any hybrid features. Of the 148 plants produced from the G. herbaceum × G. hirsutum cross, three showed a hybrid phenotype, and their hybrid status was confirmed by SSR markers. Analysis of DNA content by flow cytometry and morphological traits clearly showed that two of these plants were triploid (AAD). The third plant had a flow cytometry DNA content slightly higher than G. hirsutum. In addition, its morphological characteristics (plant architecture, presence and size of petal spots, leaf shape) led us to conclude that this plant was AAAD thus resulting from fertilization with an unreduced AA gamete of the female G. herbaceum parent. Fluorescent In Situ Hybridization (FISH) and meiotic behavior confirmed this hypothesis. To the best of our knowledge, this is the first description of such gametes in G. herbaceum, and it opens new avenues in breeding programs. Furthermore, this plant material could provide a useful tool for studying the expression of genes duplicated in the A and D cotton genome.

Dry matter yield and quality of five annual subtropical fodder crops at different irrigation levels

Maize, soybean, cowpeas, fodder sorghum and pearl millet were cultivated in a small plot trial under a rain shelter. The crops were subjected to four irrigation levels. The yields of fodder sorghum and pearl millet were better under severely water stressed conditions (W1) in comparison to that of maize. However, maize yields under control conditions (W4), were the highest. Soybean produced higher yields than cowpeas. Cowpeas were more digestible than soybeans and also had a higher crude protein content than the other four crops. Fodder sorghum and pearl millet have comparable digestibilities and crude protein contents. Maize has a high digestibility but is very poor in crude protein content. It is thus advisable to combine maize with a legume. Whether soybean or cowpeas should be considered would depend on the need of bulk or protein. Under dryland conditions (W1) fodder sorghum and pearl millet would be better choices than maize.

Effect of moringa extract on the leaf anatomy and yield potential of tomato infected by Alternaria solani

Tomato is often exposed to hormones and diseases, among other factors, to which responses in leaf anatomy and yield are observed. This study evaluated responses in the leaf anatomy of Alternaria solani infected (IN) and non-infected (NIN) tomato (Solanum lycopersicum) to moringa leaf extract (MLE) application; the responses were then correlated with fruit yield. MLE concentrations of 0.5, 0.75 and 1.5 kg L−1 (w/v) were prepared. Controls were distilled water (negative) and 50 mg L−1 benzylanimopurine cytokinin (positive). Significant interactions were observed for stomatal density (p < 0.001). MLE increased lamina thickness, stomatal density, stomatal size and yield. There was a strong positive correlation between yield, stomatal density, stomatal size and lamina thickness. Stomatal density showed the strongest correlation (r = 0.7979) with fruit yield.

Characterisation of agro-morphological traits of corchorus accessions

ABSTRACT The genus Corchorus includes nutrient-rich indigenous leafy vegetables often grown or harvested in the wild in Africa. It has potential to contribute to food security, but there is need to improve it as a crop through plant breeding. However, not much is known about the genetic variability among Corchorus species. The aim of this study was thus to characterise the available germplasm of Corchorus accessions and investigate heritability of their agro-morphological traits. Eleven Corchorus accessions (4 South African and 7 from the World Vegetable Center) were evaluated in a field study at Roodeplaat, South Africa, for their morpho-agronomic traits using a randomised complete block design with three replications across two seasons (2015/2016 and 2016/2017). Data were subjected to ANOVA, principal component analysis and cluster analysis. Broad sense heritability, genetic advance, genetic parameters and correlations were determined among the accessions and traits. The Corchorus accessions showed significant (P < .05) differences in all the quantitative traits evaluated. The data showed significant variability among the studied Corchorus accessions in their agro-morphological traits for exploitation in future breeding programmes that in turn can contribute to the improvement of this crop.

Plant anatomy as a tool for evaluating the effect of different levels of nitrogen, plant population density, row spacing and irrigation on kenaf (Hibiscus cannabinus) fibre development

Kenaf (Hibiscus cannabinus) provides high-quality fibre that is used in papermaking, building materials and absorbents. The study aims were to conduct a proper anatomical study of fibre development in kenaf stems, and to investigate if the number of fibre wedges, fibre rings (layers) and fibre bundles can be used as a tool to determine fibre development response to different agronomic practices. The practices evaluated included different nitrogen levels (0, 50, 100 and 150 kg N ha−1) under both rainfed and irrigated conditions, as well as different combinations of plant population densities (300 000, 400 000, 500 000 and 600 000 plants ha−1) and row spacing (0.17, 0.34 and 0.50 m) under rainfed conditions. In most cases N, water and plant population density were the principal factors affecting the number of fibre rings and fibre bundles, but not the number of fibre wedges. Higher levels of N and more water increased the number of fibre rings and fibre bundles, whereas at higher plant population densities, these decreased. No clear trends were observed with regards to row spacing. The results of this study suggested that under local conditions, 150 kg N ha−1 applied in two splits, 300 000 plants ha−1 and 0.50 m row spacing was the optimal combination of agronomic practices in terms of fibre development per plant. This paper gives a more complete explanation of fibre development in kenaf and shows how plant anatomy can be used as a tool to assess fibre development.

Moringa (Moringa oleifera) leaf extracts inhibit spore germination of Alternaria solani, causal agent of early blight disease of tomato (Solanum lycopersicum)

Alternaria solani is highly infective and can sporulate on tomato at 13.2 × 106 spores mL−1. The fungicidal effect of Moringa oleifera leaf chloroform and aqueous extracts (MLCE and MLAE, respectively) was investigated in vitro to determine the inhibitory effect on germination of spores (conidia) of A. solani. Mixtures of spore suspension and MLCE, as well as MLAE (1:1), were prepared and dropped on slides by micropipette with 20 µL spore suspension of A. solani and 20 µL of MLCE and MLAE. The two treatments, MLCE and MLAE, were applied at four concentrations (62.5, 125, 250 and 500 mg mL−1) and compared with negative (distilled water; no extracts) and positive (diflucan, a commercial fungicide) controls with five replicates. The two extracts showed relatively high inhibitory effects on the germination of conidia from the lowest to the highest concentration. Germination of conidia decreased with increase in the concentrations of the extracts. The study showed that 250 mg mL−1 is the optimum concentration for both MLCE and MLAE. The highest concentration inhibited germination (0.0%) in both extracts. Based on the results from the present study, MLCE and MLAE are both effective in inhibiting germination of A. solani conidia.