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Mycorrhizal root colonisation as affected by AMF inoculation
Reports on the effect of nursery inoculation on the percentage of mycorrhizal root colonisation are contradictory. Martin (2007) found a low mycorrhizal colonisation (< 10%) with inoculated tomato seedlings, whereas Karagiannidis et al. (2002) obtained nearly 50% root colonisation. Generally, high mycorrhizal infection is hardly observed in tomato seedling production. Chandanie et al. (2009) argued that even a low level of colonisation (< 13%) before transplanting should be considered adequate for successful establishment as these fungi would spread rapidly to new roots after transplanting (Bierman & Linderman, 1983). Following nursery mycorrhizal inoculation, Latef and Chaoxing (2011) found more than 50% mycorrhizal root infection in greenhouse produced tomato.
Under field production, farmers face the challenge of low levels of root colonisation. Cavagnaro and Martin (2010) conducted a field survey which included the majority of processing tomato farms in southeastern Australia. More than 75% of the farms had less than 4% mycorrhizal colonisation of the roots. In almost 40% of the cases, mycorrhizal root colonisation was completely absent. Soil fumigation was put forward as the main limiting factor. Unfortunately, data on the natural veld area was not available. In California, the colonisation of tomato roots by AMF is typically in the range of 7–37% for fresh market organic tomato farms, (Cavagnaro et al., 2006). Soil disturbance and cultural practices negatively affect the performance of mycorrhiza in the field, the level of native mycorrhiza in these studies might well be too low or nil to permit any symbiosis. Low AMF colonisation in field production has also been attributed to (i) the use of inappropriate strains, (ii) relatively high available soil P (Strzemska, 1975) and (iii) microbial competition in the rhizosphere.
Effect of nursery inoculation with AMF on fruit yield and quality
From a practical viewpoint, the most important growth response to AMF inoculation should occur in yield, because it is the major variable by which production efficiency is measured (Martin, 2007). Generally, results on the effect of AMF inoculation on yield improvement had been contradictory or unsatisfactory. Cavagnaro et al. (2006) did not find any yield increase with organically produced tomato. Ryan and Angus (2003) studied the role of AMF in nutrition and yield of wheat and field pea in a 2-year crop sequence experiment on red a loam soil in Australia, where high root colonisation did not translate into increased growth or yield of wheat or pea. Ryan and Angus (2003) argued that AMF was unimportant for productivity of the major field crops. Nursery inoculation with AMF increased tomato yield by ca. 40% on a processing tomato farm (Martin, 2007). In another study (Regvar et al., 2003), two month old tomato seedlings were inoculated with a mixture of indigenous mycorrhiza and transplanted into pots in a greenhouse and three months later, the plants were transplanted into the field and allowed to grow for a further two months. A 26% increase in yield was observed when using inoculated seedlings. The methodology followed by Regvar et al. (2003) is not the norm since growers in general use young seedlings (3-4 weeks) with inoculation being done during sowing. Increased yield with AMF was previously shown to correlate with P supply or soil P status. In a field experiment, inoculating tomato seedlings with the AMF (G. fasiculatum) increased tomato yield by up to 13% (Mohandas, 1987). Li et al. (2005) examined the interactive effect of AMF and P supply in wheat, where with low P, AMF plants produced lower grain yield per plant, whereas with higher P, AMF plants produced higher grain yields than uninoculated plants. Similarly, Douds and Reider (2003) observed that inoculating tomato with AMF before transplanting increased yield in high-P containing soils.
Martin (2007) found a 4% decrease in fruit brix despite an increase in fruit P, Zn and Ca contents of AMF-inoculated plants when compared to the uninoculated plants. Martin (2007) argued that the decrease was due to increased demand for carbohydrates by the increased number of fruits in AMF-treated plants. Cavagnaro et al. (2006) observed 50% higher fruit Zn content in AMFtreated plants when compared to the control. The uptake of Zn has a profound impact in human health and Cummings and Kovacic (2009) reported that Zn deficiency in humans altered the immune and gastrointestinal systems, blood cell development and thyroid hormone metabolism, as well as the activities of pancreas, liver and brain, and can also increase the risks of diabetes, coronary artery disease and cancer. Mycorrhizal association improved tomato fruit quality by enhancing ascorbic acid content and reducing the acidity (Subramanian et al., 2006). Symbiosis with AMF can also stimulate the synthesis of secondary metabolites such as phenolic acids, anthocyanins, flavonoids, phytosterols, stilbenes, vitamins and carotenoids, which are beneficial for human health (Hooper & Cassidy 2006; Kirby & Keasling 2009; Gianinazzi et al., 2010).
CHAPTER 1: GENERAL INTRODUCTION
1.1 Rationale
1.2 Objectives
1.3 Research approach and thesis outline
CHAPTER 2: LITERATURE REVIEW
2.1 Arbuscular mycorrhizal fungi
2.2 Trichoderma
2.3 Arbuscular mycorrhizal fungi and Trichoderma
CHAPTER 3: GROWTH, YIELD AND VERTICILLIUM WILT INCIDENCE OF TOMATO(SOLANUM LYCOPERSICUM) AS INFLUENCED BY DIFFERENT PRE-SOWING TREATMENTS
3.1 Abstract
3.2 Introduction
3.3 Materials and methods
3.4 Results
3.5 Discussion
CHAPTER 4: TOMATO (SOLANUM LYCOPERSICUM L.) SEEDLING GROWTH AND DEVELOPMENT AS INFLUENCED BY TRICHODERMA HARZIANUM AND ARBUSCULAR MYCORRHIZAL FUNGI
4.1 Abstract
4.2 Introduction
4.3 Materials and methods
4.4 Results
4.5 Discussion
CHAPTER 5: YIELD AND NUTRIENT CONTENT OF GREENHOUSE PRODUCED TOMATO (SOLANUM LYCOPERSICUM L.) AS INFLUENCED BY TRICHODERMA HARZIANUM AND GLOMUS MOSSEAE INOCULATION
5.1 Abstract
5.2 Introduction
5.3 Materials and methods
5.4 Results
5.5 Discussion
CHAPTER 6: RESPONSE OF TOMATO (SOLANUM LYCOPERSICUM L.) TO NURSERY INOCULATION WITH TRICHODERMA HARZIANUM AND ARBUSCULAR MYCORRHIZAL FUNGI UNDER FIELD CONDITIONS
6.1 Abstract
6.2 Introduction
6.3 Materials and methods
6.4 Results
6.5 Discussion
CHAPTER 7: EFFECT OF ARBUSCULAR MYCORRHIZAL FUNGAL INOCULATION AND BIOCHAR AMENDMENT ON GROWTH AND YIELD OF TOMATO (SOLANUM LYCOPERSICUM L.)
7.1 Abstract
7.2 Introduction
7.3 Materials and methods
7.4 Results
7.5 Discussion
CHAPTER 8: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
