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Impact of Arbuscular Mycorrhizal Fungi on Growth of Banana Genotypes in Three Different, Pasteurized and Non-pasteurized Soils of Rwanda S.V. Gaidashova,1* A. Nsabimana,2 P.J.A. van Asten,3 B. Delvaux,4 A. Elsen5 and S. Declerck4 1 Rwanda Agricultural Board (RAB), Kigali, Rwanda; 2Kigali Institute of Science and Technology (KIST), Rwanda; 3International Institute of Tropical Agriculture (IITA), Kampala, Uganda; 4Université Catholique de Louvain (UCL), Louvain-la-Neuve, Belgium; 5Soil Service of Belgium, Leuven, Belgium
Abstract Arbuscular mycorrhizal (AM) fungi are known to improve the growth of many crops of agricultural importance. The amplitude of this growth improvement may vary depending on soil type. Here, we report the effect of the application of indigenous AM fungi, isolated from a Nitisol from Kirehe (eastern Rwanda), on the growth and root characteristics of three banana (Musa spp.) genotypes: ‘FHIA-17’ (AAAA), ‘Musakala’ (AAA-EA) and ‘Sukali Ndiizi’ (AAB), grown in pasteurized and non-pasteurized Acrisol, Ferralsol or Nitisol. Root characteristics differed significantly between soil types (P < 0.001) and banana genotypes (P < 0.05). The poorest root development was observed on the Acrisol and the best on the Nitisol, irrespective of genotype. ‘Musakala’ had a smaller root system than ‘FHIA-17’ and ‘Sukali Ndiizi’. Inoculation resulted in highly significant (P < 0.001) differences in frequency of root colonization between soil types in all genotypes and treatments, with the highest frequency observed in the Nitisol and Ferralsol and the lowest in the Acrisol. Inoculation increased plant growth and dry weight (P < 0.05) but the effect was less marked in nonpasteurized treatments than in pasteurized treatments in all soils and genotypes. The exception was the Ferralsol, where pasteurization did not result in a significant increase in plant growth. The highest relative plant growth increase caused by AM fungi was observed in the Acrisol. This was observed for all genotypes and treatments and could possibly be linked to the greater limitations to root growth in this soil type. Poorer root development of ‘Musakala’ coincided with its highest response to the AM fungi inoculation compared with other genotypes, which suggested its higher AM fungal dependency.
9.1 Introduction The important role of East African highland bananas (Musa spp., AAA-EA) as a staple crop,
cash crop and essential element in landscape and soil conservation in the East African highlands (EAH) has been emphasized by different authors (Davies, 1995; Rishirumuhirwa, 1997;
* E-mail:
[email protected]
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©CAB International 2013. Banana Systems in the Humid Highlands of Sub-Saharan Africa (eds G. Blomme, P. van Asten and B. Vanlauwe)
Impact of Arbuscular Mycorrhizal Fungi
Kangasniemi, 1998; Karamura et al., 1999). There is high soil type diversity in the EAH region (Eswaran et al., 1989) and bananas are grown under a wide range of agro-ecological conditions (Davies, 1995). However, declining yields throughout the region compromise production (Okech et al., 2004, 2005; Baijukya et al., 2005; Macharia et al., 2008). Among the major constraints causing yield decline are low inherent soil fertility (Sanchez et al., 1997), inadequate soil management (Bekunda et al., 2002), nutrient mining (van Asten et al., 2004, 2006) and pests and diseases (Tushemereirwe and Bagabe, 1999; Okech et al., 2002; Mwangi and Nakato, 2009). To overcome some of these yield constraints, the application of beneficial soil microorganisms such as arbuscular mycorrhizal (AM) fungi has received increasing attention (Jaizme-Vega and Azcón, 1995; Declerck et al., 2002; Jefwa et al., 2008). The potential impact of AM fungi in helping to overcome plant nutrient constraints in EAH cropping systems may be particularly high (Jefwa et al., 2008), as these systems generally do not receive chemical inputs (i.e. inorganic fertilizers and pesticides) and are, therefore, more AM fungi ‘friendly’ (Adriano-Anaya et al., 2006; Jansa et al., 2006). The positive effect of AM fungi on banana growth has been shown in several studies conducted under controlled conditions (Jaizme-Vega and Azcón, 1995; Yano-Melo et al., 1999; Thaker and Jasrai, 2002). The magnitude of the effect of the AM fungi on the growth of annual crops may vary with soil type (Plenchette et al., 1989; Plenchette, 2000), but it is still unknown how the response of banana to AM fungal inoculation is modulated in different soil types. In the present study, we investigated the effects of soil inoculation with AM fungi on banana growth parameters in three soils differing in physical and chemical properties and three banana genotypes differing in root system development. Soils were either pasteurized or non-pasteurized, and the effects of the following soil treatments were evaluated: (i) natural microflora (non-inoculated, nonpasteurized soil, NI-NP) alone; (ii) natural microflora in combination with introduced AM fungal inoculum (inoculated, non-pasteurized
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soil, I-NP); (iii) inoculated AM fungi alone (inoculated, pasteurized soil, I-P); and (iv) absence of inoculum (non-inoculated, pasteurized soil, NI-P).
9.2 Material and Methods 9.2.1
Biological material
Micropropagated banana plantlets (Musa spp. ‘FHIA-17’ (AAAA), ‘Musakala’ (AAA-EA) and ‘Sukali Ndiizi’ (AAB)) were supplied by the Agro-Genetic Technologies Laboratory (Uganda). Plantlets measuring 5 ± 1 cm height with two fully developed leaves were received in nutrient agar (Murashige and Skoog, 1962). The genotype ‘FHIA-17’ is an improved tetraploid hybrid with a welldeveloped root system and was recently introduced to the EAH region, while ‘Sukali Ndiizi’ and ‘Musakala’ are traditional cultivars with medium and less developed root systems and have been grown in EAH region for more than 50 years. The inoculum consisted of a natural mixed population of AM fungi containing the genera Rhizophagus, Gigaspora and Scutellospora (not identified at the species level) isolated from a banana farm at Kirehe (eastern Rwanda). Pot cultures were initiated from banana root fragments and multiplied on leeks for 6 months. Fresh leek roots were used for inoculation, and these were colonized at a frequency of 89% and intensity of 73%. The fresh soils used in the experiment originated from Huye, southern Rwanda (Acrisol: 56% sand, 37% clay, 7% silt texture with gravel ratio above 10% soil weight and low water-holding capacity), Rusizi, southwestern Rwanda (Ferralsol: 80% clay, 12% sand and 8% silt, with thin capillaries of
