Review: Agroforestry Species Have Negative Allelopathic Effect on Food and Fodder Crops

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Published on International Journal of Agriculture & Agribusiness
ISSN: 2391-3991, Volume 2, Issue 2, page 78 – 83
Publication Date: March 11, 2019

Kugedera, A. T & Kokerai, L. K
Department of Agriculture Management, Faculty of Agriculture, Zimbabwe Open University
Department of Livestock, Wildlife and Fisheries, Great Zimbabwe University
Masvingo, Zimbabwe

Journal Full Text PDF: Review: Agroforestry Species Have Negative Allelopathic Effect on Food and Fodder Crops.

Abstract
The aim of the review was to assess the effects of different allelochemicals contained in different tree species used for food and fodder. Information was gathered from different papers using secondary data and an essay was prepared covering different tree species used in Agroforestry. Many tree species were found to have negative allelopathic effects on food crops such as maize, covo and wheat. Eucalyptus species were found to contain allelochemicals which have negative effects on growth of food crops.

Keywords: Agroforestry, allelopathic, food crop, fodder crop & negative effects.

1. INTRODUCTION
Allelopathy is defined as direct or indirect effects of allelochemical compound resulted from organism which may have inhibitor or stimulator effects on the same or different organisms (Saberi et al., 2013). Synthesis of biologically active molecules produced by plant and their residue may convert to other forms and influenced on growth of similar or non-similar (Bogatek et al., 2005). Allelopathy is a reciprocal effect of biochemical compounds among all plants and micro-organisms. These compounds can be released in environment in form of gases and or by leaching from aerial body, leaking from root and /or decomposing plant residues (Lu and Yanar, 2004). Allelopathy caused decrease in plant growth more than what caused by competition in plants and sunlight, water and nutrition.

2. ALLELOPATHY CLASSES
Allelopathic inhibition is complex and can involve the interaction of different classes of chemicals, such as phenolic compounds, flavonoids, terpenoids, alkaloids, steroids, carbohydrates, and amino acids, with mixtures of different compounds sometimes having a greater allelopathic effect than individual compounds alone (Rizvi et al., 1999). Furthermore, physiological and environmental stresses, pests and diseases, solar radiation, herbicides, and less than optimal nutrient, moisture, and temperature levels can also affect allelopathic weed suppression (Stamp, 2003). Different plant parts, including flowers, leaves, leaf litter and leaf mulch, stems, bark and roots, soil, and soil leachates and their derived compounds, can have allelopathic activity that varies over a growing season. Allelopathic chemicals or allelochemicals can also persist in soil, affecting both neighbouring plants as well as those planted in succession (Rizvi et al., 1999). Although derived from plants, allelochemicals may be more biodegradable than traditional herbicides, but allelochemicals may also have undesirable effects on non-target species, necessitating ecological studies before widespread use (Ferguson et al., 2013).
Allelopathic compounds restrict plant growth through negative interactions with important physiological processes such as changes in cell wall structures, prevention of cell division and activity of some enzymes in both food and fodder crops (Rice, 1984). Allelopathy compounds affects the equilibrium of plant hormones, pollen tube germination, absorption of nutrients, displacement of stomata, photosynthesis, respiration, protein synthesis, pigment and changes in DNA and RNA structure (El-Khatib et al., 2004).

3. EFFECTS OF ALLELOPATHY IN Eucalyptus SPECIES
Eucalyptus camaldulensis is one of agroforestry species suitable for wind breaks. If Eucalyptus camaldulensis is used as wind breaks and crops are grown these windbreaks are affected by allelopathic compounds produced by Eucalyptus camaldulensis (Saberi et al., 2013). Allelopathy chemicals in Eucalyptus camaldulensis could effect on germination and early seedling growth of Vicia villosa, Onobrychis sativa, Festuca arundinacea and Trifolium rigidom (Saberi et al., 2013). According to Saberi et al. (2013) Trifolium rigidom and Onobrychis sativa are more sensitive to allelopathic chemicals from Eucalyptus camaldulensis than all other species. These allelopathic chemicals decreases germination because they inhibit hormones especially gibberellins. Allelopathy from Eucalyptus camaldulensis causers changes in enzyme activity which restrict the conversion of nutritive compounds during germination of seeds (Lu and Yanar, 2004; Saberi et al., 2013).
Allelochemicals in Eucalyptus camaldulensis causes delay or stimulate in using nutritive matter that can cause lack of Production of Respirable Vesicles and finally result in lack of Adenosine triphosphate (ATP) in seeds exposed to allelochemical compounds (Saberi et al., 2013; Farajo et al., 2012). Allelochemical compounds restrict metabolic energy by disorder in respiration rate consequently decreased the early growth of seedling (Lu and Yanar, 2004; Rice, 1984).Growth of radicle and shoots of food crops such as Zea mays and Glycine max is decreased when these crops are grown near or within Eucalyptus camaldulensis and other Eucalyptus species because these food crops are exposed to allelochemical compounds (Bogatek et al., 2005). Allelochemicals in Eucalyptus grandis, Eucalyptus tereticornis and Eucalyptus camaldulensis inhibit cell division and elongation of cells. They also decrease stimulate effect of gibberellins and acetic acid in plants (Lu and Yanar, 2004; Bogatek et al., 2005; Saberi et al., 2013). Allelopathic compounds could disorder in vital activities of food and fodder crops by other mechanisms such as restriction of nutritive absorption, disorder in respiration, oxidative phosphorylation and photosynthesis ( Saberi et al., 2013).
Time, environmental conditions, and plant tissue all factor into variations in allelochemical concentrations in the producer plant (Stamp, 2003; Saberi et al., 2013). Foliar and leaf litter leachates of Eucalyptus species are more toxic than bark leachates to some food crops. The allelopathic potential of Ipomoea cairica (mile-a-minute vine) is significantly greater at higher environmental temperatures (Ferguson et al., 2013). Studies by Stamp (2003) indicated that soil biota reduced the allelopathic potential of sticky snakeroot (Ageratina adenophora). Red fescue infected by a fungal endophyte produced more allelochemicals than plants that were not infected (Rizvi et al., 1999; Stamp, 2003). Allelopathic chemicals in Eucalyptus tereticornis inhibit growth and yield in cowpeas if grown together or near each other (Rizvi et al., 1999).
Eucalyptus globulus produces volatile emanations that inhibit root growth of Cucumis species seedlings and the growth of hypocotyls but not the roots of Eucalyptus globulus seedlings (Bhatt and Chauhan, 2000). Leaf leachates from Eucalyptus globulus inhibits seed germination of Glaucium flavus (Singh and Bawa, 1982). Similar to Eucalyptus globulus is Grevillea robusta which produces allelochemicals that inhibits growth of Glycine max and Zea mays (Bhatt and Todaria, 1990). Bark and leaf extracts from these agroforestry species were found to be most toxic to food and fodder crops (Bhatt and Chauhan, 2000). Quercus species produces allelochemicals which also have same effects to food crops such as Triticum aestivum and Brassica campestris. Allelochemicals from Quercus species suppress germination, plumule and radicle length if all food crops (Bhatt et al., 1993).

4. EFFECTS OF ALLELOPATHY IN Mangifera indica
Allelopathy in Moringa oliefera have been found to inhibit germination of seeds of Echinochloa crusgalli (barnyard grass), Glycine max and Brassica napa (turnip) by leachates of leaf, wood and leaf litter (Melkania, 1984). Zea mays and Brassica campestris (mustard), Pinus sativum (pea) and Triticum aestivum germination was also inhibited by litter extract from Moringa oliefera (Rice, 1984; Hossain et al., 2012). Moringa oliefera is one of trees which can be widely used as vegetables and if consumed in large and when mature can have negative effects. In some areas it is used as fodder crop and the presence of allelopathic chemicals may hinder animal growth if consumed at maturity stage because the quantity of these allelochemicals could have increased (Hossain et al., 2012).
Allelopathic chemicals in dried Mangifera indica leaf powder completely inhibit the sprouting of purple nut sedge tubers (Stamp, 2003; Ferguson et al., 2013). This also coincides with research by Musvoto and Campbell (1995) who found that intercropping of maize with Mangifera indica in Mangwende area showed reduced growth and maize yield. Mangifera indica are generally perceived as having negative effects on crop growth and yield (Musvoto and Campbell, 1995). Leaf powder from dried Mangifera indica leaves produces allelopathic chemicals which acts as acids by reducing soil pH to acidic hence reducing the growth of food crops.

5. EFFECTS OF ALLELOPATHY IN Juglans nigra
Juglans nigra (black walnut) is another agroforestry species which is used for hedgerow inter-cropping (alley cropping) with Zea mays and Glycine max (Jose and Gillespie, 1998). Allelopathy in Juglans nigra inhibits leaf respiration through inhibiting oxygen uptake by mitochondria of Zea mays and Glycine max. Allelopathy in this agroforestry specie also affects fodder trees such as Leucaena leucocephala if grown together and other woody species (Jose and Gillespie, 1998). Allelopathic chemicals in Juglans nigra also cause photosynthetic reductions in Glycine max leaf disks (Jose and Gillespie, 1998). Rows of Juglans nigra inter-planted with Zea mays in hedgerow inter-cropping system reduces Zea mays yield attributed to production of juglone, an allelopathic compound from Juglans nigra found 4.25m from the tree (Ferguson et al., 2013).