Investigation of arbuscular mycorrhizal inoculation on growth of tropical fruit seedlings under saline, flooding and nutrient stress conditions

Abstract

Researchers continue to demonstrate the contribution of Arbuscular Mycorrhiza fungi on crop productivity, especially under adverse soil conditions. In sub Saharan Africa, mycorrhizal studies on major fruit crop seedlings have received little attention. Salt stress experiment was undertaken in mycorrhizal and non mycorrhizal passion fruit and mango seedlings subjected to moderate and high salt stress. Data was collected on root colonisation, growth, biomass and nutrient uptake. The study found out that mycorrhizal colonization reduced under salt stress conditions. Plant height, leaf number, chlorophyll content, root, stem and leaf fresh and dry weights was greater in mycorrhiza-inoculated than in un-inoculated seedlings under salt stress conditions. Total leaf accumulation of P and K was higher in mycorrhizal than in non-mycorrhizal plants while Na concentrations were lower under both control and medium salt stress conditions. This study found that a reduction in Na uptake, with a concomitant increase in P and K absorption and high leaf chlorophyll content play a role in alleviating salt stress in plants growing in mycorrhizal passion fruit and mango seedlings growing in saline soils. To investigate the role of mycorrhiza on flooding stress, data was collected on proline, chlorophyll and carotenoid content, total soluble sugars, mycorrhizal root colonization and nutrient uptake in passion fruit subjected to root-zone flooding for 7, 14, 21 and 28 days. The seedlings were grown in sterilized sand under low phosphorus regime for 12 weeks before flooding was initiated. Mycorrhizal inoculation induced greater root, stem and leaf fresh and dry weights, and maintained greater leaf area as opposed to leaf abscission that occurred more rapidly in non-mycorrhizal seedlings under flooding. Chlorophyll a,b and total chlorophyll declined, while carotenoids increased rapid in non-mycorrhizal seedlings under flooding. A rapid increase in leaf proline and a slow decline in total soluble sugars was observed in mycorrhizal seedlings under flooding. Flooding induced a reduction but did not completely inhibit mycorrhizal root colonization. The leaf nitrogen and phosphorus contents declined under flooding, with the decline occurring more rapidly in non-mycorrhizal seedlings. This study found out that increased production of proline, maintenance of optimum nutrient supply in the leaves and delay in degradation of leaf chlorophyll aids mycorrhizal passion fruit seedlings to delay the adverse effects of flooding. The effect of Arbuscular mycorrhiza fungi on growth, nutrient uptake and root infectivity was also determined in passion fruit, rough lemon, papaya, mango and avocado seedlings raised under four phosphorus levels in sand culture and also in low nutrient sterilized and unsterilized media. Arbuscular mycorrhiza increased the leaf area and the root, leaf and stem fresh and dry weights and also induced an increase in the uptake of phosphorus, nitrogen and potassium in the leaf tissues. This study indicated that AM fungi improved the capacity of tropical fruit seedlings to absorb and utilize plant nutrients possibly by increasing the effective root surface area from which available form of nutrients are absorbed and also by increasing access of roots by bridging the depletion zones. Inoculating seedlings with arbuscular mycorrhizal fungi helps to alleviate the adverse effects of global warming and climate change. As a low cost technology, arbuscular mycorrhizal inoculation is recommended as part of the regular practise for incorporating into nursery media used for tropical fruit seedling propagation in Kenya.