Potentials of Arbuscular Mycorrhiza Fungus in Tolerating Drought in Maize (Zea mays L.)

Maize is one of the most important cereal crops widely grown for food, feed, and fodder/forage throughout the world in a range of agroecological environments. Drought stress continues to haunt the maize farmers across south western part of Nigeria, thereby leading to low quantity of this essential staple food in the market. Efforts have been made to enhance the growths and yields in maize by investigating the influence of Arbuscular mycorrhizal fungus (Gigaspora gigantea) on the tolerance of maize to drought stress. The experiment was conducted in the teaching and research farm of Babcock University, Ilishan-Remo, Nigeria. The experiment was laid out in a complete randomized design with four replicates. Data were collected on eight morphological drought related characters. The objective of this research work was to evaluate the morpho-agronomic responses and potential of Gigaspora gigantea colonization in maize drought tolerance, and also to select parents in maize breeding for improved yield related components. The combined analysis of variance showed significant (P < 0.05) treatment effect on majority of the traits evaluated. The treatments of Arbuscular Mycorrhiza Fungus (AMF) produced significant higher growth related traits suggesting that AMF treated plants had higher potential in influencing the tolerance to drought. Accession 3 was considered best for most of the traits studied and can be selected as parents in maize breeding for yield related components.


Introduction
Maize (Zea mays L.) also known as corn is an important monocotyledonous plant of the family Poaceae.It is the most widely grown grain crop in the world as a direct staple food for millions of individuals and, through indirect consumption as a feed crop, is an essential component of global food security [1]- [3].Maize becomes stressed by drought at the reproductive period, however, the development and adoption of drought-tolerant varieties are seen as a long-term solution to many of the problems plaguing drought-prone maize production regions around the globe [2].The change in global climate is now generally considered to be underway [4] and is expected to result in a long-term trend towards higher temperatures and an increased incidence of drought in specific regions.There is significant amount of yield losses due to water stress in both temperate and tropical environments [5].Since water availability is variable across fields and farmers typically grow only one hybrid in a particular field, a moderate amount of drought tolerance is necessary in all maize hybrids [6]; the use of drought-tolerant cultivars may be the only economical option for many small-scale farmers [7].The utilization of Arbuscular mycorrhizal fungi can enhance yield stability by improving drought tolerance which can be a major solution to stabilizing global maize production.Maize agronomic responses to drought stress have been detailed in multiple review and research articles [8]- [12].
G. gigantea plays an important ecological role and symbiotic relationship with the root of higher plants by contributing significantly to plant nutrition and promoting growth in the cultivation of agricultural crop species, such as hardwood tree seedlings, corn (Zea mays), carrot (Daucus carota), grape (Vitis vinifera) and soybean (Glycine max) [13]- [15] and has been shown to increase the productivity of a variety of agronomic crops including maize [16].Horticultural plants can utilize AMF to increase their growth and yield responses in drought stress condition to well-watered conditions due to mobility of nutrient that is limited under drought conditions [17] [18].In case of soybean, Gigaspora gigantea can be used in combination with Bradyrhizobium japonicum, a nitrogen fixing bacterium, to promote plant growth [19].The colonization of some cuttings of yew (Taxus x media var.densiformis) plant inoculated with G. gigantea has been reported of higher levels of chlorophyll [20], [21].However, in maize, the most widely recognized contribution of AM fungi to host-plant nutrition involves their ability to extract Phosphorus from outside the Phosphorus depleted regions near the plant roots [22]- [27] and non-AM-host weed suppression [28].Yet the positive effects of AM fungi on host-plant growth and development are not only noticeable in low soil fertility conditions [29], [30] but also in drought environments [17] [20], improved soil structure may also trigger plant growth and development [31].The potential of G. gigantea in integrated striga management has also been reported in maize but the information on influence on drought tolerance and growth of maize is limited [32].Although, drought can strike at any time, the plants are most prone to damage due to limited water.Some of the drought-tolerance related traits include plant height, number of leaves, stem girth.It has however been studied recently that AM fungi has positive influence on the performance of these traits.Therefore, this study aimed at investigating the influence of G. gigantea on drought tolerance and growth of maize accessions.

Materials and Methods
The experiment was conducted at the teaching and research farm of the Department of Agriculture, Babcock University teaching and research farm Ilishan Remo Ogun State, South western Nigeria which is situated at the altitude (6˚ 52ʺ 00 N and 3˚ 43ʺ 00 E) from January to March, 2012.Maize accessions were obtained from four different market locations in Ogun State, Nigeria (Table 1).The Arbuscular mycorrhizae species collected from Soil Biology Unit of the Department of Botany, University of Ibadan, Ibadan, Nigeria was a soil inoculum obtained from extracted spores using a wet-sieving technique according to the procedure described by Sieverding and Schenck (1989).The experiment was laid out in a complete randomized design and replicated four times.The treatments were; T1 = Maize + AMF only; T2 = Maize + AMF + Water only and T3 = Maize only which served as contro l.50 Spores of AMF (G.gigantea) in mixtures soil and root fragments were inoculated in 8 kg plastic pots filled with sterile depleted soil according to the procedure described by [33] Each treatment consists of 3 rows of 60cm per accession, with spacing of 30 cm between rows.The treatments were applied four weeks after planting to assess the tolerance and susceptibility levels of drought in the accessions.Weed control was carried out through manual weeding.The data collected on morphological drought-related traits of maize using descriptive sampling at 4 and 6 weeks after planting were; plant height, stem length, leaf length, leaf width, number of leaves, number of node, node per length of plant, stem girth.The data obtained were subjected to analysis of variance using [34].Significant difference between treatment means were separated using Duncan Multiple Range Test at P < 0.05.

Result and Discussions
The analysis of variance shows that the height of maize plant in day after treatment (DAT) for AMF only and AMF + Water treated plants were significantly different(P < 0.05) from control which had the least value of 64.20 cm (Table 2).This implies that maize accession from Ilishan has the potential to resist drought, while untreated plant (Control) could not.On third DAT, there were significant differences in accessions from Ikene, Iperu and Ilara for plant height, while treated plant with AMF only in accession from Ilishan-Remo was significantly different from other treatments.Also maize treated with AMF + water in Ikene and Ilara accessions were higher and significantly different from other treatments and control, while AMF only in Ilishan-Remo and Iperu accessions were significantly different from Maize treated with AMF + Water and control.This conforms to the observation of [28].The number of leaves per plant for Ilishan-Remo accession were not significantly different from maize treated plants after the 3DAT and 5DAT as well as plant treated after 9DAT for Ikene accession, while significant effect of the treatments were observed for other accessions except Ikenne (Table 2).Plants treated with AMF + water was significantly higher than other treatments and control in Ilishan-Remo, Ikenne and Iperu accession.On the other hand, the varietal influence favored the performance of plants treated with AMF only at the initial stage after treatments for production of leaves.Also, there were significant different in leaf length for all the treated maize accessions (Table 2).Similar observation was reported by [35].Again, the result from Table 3 shows that the leaf width of maize plant in 2DAT for AMF + Water treated plants were significantly different from controls which had the least value of 2.80 cm.On the third DAT, there were no significant differences (P > 0.05) in leaf width from all the treatments from Ikenne, while treated plant with AMF + Water only in Ilishan-Remo was significantly different (p < 0.05) from other treatments of other accessions.At 4DAT, the control plants were not significantly different in all the locations, but at 5DAT, plants treated with AMF only were significantly different from control with the least value of 3.40 cm in Ikene (Table 3).For number of node at 1DAT, there were significant differences for all the treatment in Ilishan Remo and Iperu accessions, while significant differences were not observed in all the treatments in Ikenne and at 2DAT for all the treatments in Ilishan-Remo.
At 3DAT, the number of nodes had the least value of 2.00 cm for control plant in Ilara accession, while plant treated with AMF only was significantly different from other treatment including control in Iperu for all the days after treatment.At 5DAT, the node per length of 6.00 cm in AMF + Water treated plant was significantly different from other treatment in which with 3.95 cm was the least for all the accessions (Table 3).The result of the growth response of maize to AMF treatment at different days is shown in Table 4.At 1DAT, the stem height of AMF treated plant was significantly different from untreated plants while plants treated with AMF only and AMF + Water at 2DAT, 3DAT, 4DAT and 5 DAT were significantly different from untreated plant.The stem girth at 1DAT in AMF + Water only was significantly different from untreated plants but at 4DAT, there were no significance differences in all the treatments for Ilishan-Remo accession (Table 4).This agrees with the findings of [36].
Figure 1 shows the effect of AMF + Water on drought tolerance of maize, Figure 2 also shows the maize plant treated with AMF only, while the effect of water on maize is shown in Figure 3.

Conclusion
The results showed that maize accession treated with AMF produced significant higher growth related traits suggesting that AMF treated plants had high potential in influencing the tolerance to drought.The use of AM fungus can be recommended for farmers since most agricultural crops can perform better and more productive      when well colonized by AM fungus, especially in the cultivation of Maize.The farmers should be encouraged to use AMF as it is environmentally friendly in preventing water pollution and reducing soil toxicity, and required no specialized skill for its application and there is no need of frequent application.
10b 4.10c DAT = day after treatment, Accession = A, Mean with the same value in the column are not significantly different P < 0.05.

Table 1 .
Accessions and their sources.

Table 2 .
Growth response of maize accessions in treatment combinations of G. gigantea at different days.

Table 3 .
Effect of AMF treatments on leaf width, number of node and node per length at different days.

Table 4 .
Growth response of maize to AMF treatments at different days.