Germination and seedling growth response of mango (Mangifera Indica L.) cultivars to different nursery potting media

Background: Mango is an important cash crop greatly contributing for food security of fruit growers in northwestern parts of Tigray region, northern Ethiopia. However, information was critically lacking with respect to germination and growth response of mango rootstock to varying compositions of growing media in the region. Thus, an experiment was conducted during 2018 to evaluate germination and seedling growth response of mango cultivars to different combinations of nursery potting media in a net house at Indasellassie. Seeds of Local, Dodo and Keitt cultivars of mango were sown in full top soil (M1); top soil: sawdust: sand (3:2:1)(M2); top soil: FYM (Farmyard manure): sand (3:2:1) (M3); and top soil: FYM: sawdust: (3:2:1)(M4). Randomized complete block design in a factorial arrangement with three replications were used. Data on germination and growth parameters were collected and analyzed using GenStat software. Results: The findings of the experiment revealed that mango cultivar had significantly affected most of the germination and growth parameters except shoot number. Moreover, potting media affected most of the parameters except days to germination, germination percentage, stem diameter, root number, and shoot number. Interaction effects of cultivar and growing media significantly affected all parameters except internode length, shoot number and stem diameter. Accordingly, interactions of local mango cultivar and M3 media combination gave the highest for most of the parameters with the order of M3 = M1 = M4 > M2 for germination percentage, M3 = M1 > M4 = M2 for plant height, M3 > M1 > M2 = M4 for leaf number, M3 > M1 > M4 > M2 for leaf area, M3 = M1 > M2 = M4 for stem diameter, M3 = M1 > M2 > M4 for root number, M3 > M2 > M1 = M4 for root length, M3 > M1 > M2 = M4 for fresh weight, M3 > M1 = M2 = M4 for dry weight and Vigorosity II of mango. Conclusion: Considering better mango performance on seed germination, seedling growth and establishment in the study area, mango growers should use Local mango cultivar with soil potting media combinations of top soil: FYM: sand in the ratio of 3:2:1 for improving productivity and food security.

worldwide [2]. Mango is known as the king of the fruits due to its excellent flavor, delicious taste and high nutritive values that makes the crop valued for both food and nutritional security especially for developing countries like Ethiopia where the realization of food and nutritional security is still a challenge [3]. The crop can be consumed as a raw, canned, or juice which provides sufficient amount of dietary antioxidants, such as ascorbic acid, carotenoids, and phenolic compounds and additionally a remarkable amount of dietary fiber, and vitamin A [4]. Mango is one of the most widely grown among the fruit crops cultivated in Ethiopia preceded only by banana in terms of economic importance [5]. In Tigray region, the potential area for mango production is in estimated at about 118.2 hectare [4]. According to Mekonnen [6], an attractive and delicious tropical and temperate fruits including mango are much in demand in the local markets in Tigray (Additional file 1).
The productivity of mango in Ethiopia is very low compared to the crop potential, about 20-30 ton/ha [7,8]. Various factors govern crop productivity but, genetic and environmental are well known. Nowadays, the government has been introducing new improved varieties in Ethiopia. However, as compared to different mango growing nations, varieties of improved mango seedlings distributed to farmers for commercial production in Ethiopia are few [9]. Moreover, the supply of suitable root-stock mango seedlings in Tigray region is very limited [10]. Consequently, nursery potting media believed to have contributed to low viability and productivity of mango in the region. Mango plants are multiplied asexually through grafting and each plant is made up of the rootstock which provide root system and the scion forming the tree canopy. Both of these parts play an equally vital role in the life of a tree. The rootstock has great influence on the vigour, longevity and productivity of the scion variety [11]. Moreover, quality and composition of fruits also been affected by the root stock [11]. Thus, raising good quality rootstocks is very important for sustainability of the orchard. Similarly, nursery potting medium is most important input for healthy, uniform and quality rootstock seedling production. Apart from the selection of proper ingredients, it is also necessary to maintain the porosity of the potting mixture so that proper development of roots takes place [12]. In North-western zone of Tigray region orchard owners usually use varied levels and types of nursery potting media although majority use top soil: FYM: sand in the ratio of (3:2:1) together with local cultivar mango seedling root stock. Likewise, in the study area, there was limited research based information on germination and growth performance of existing and available mango rootstock cultivars to different nursery potting media compositions. Hence, it was high time to consider the evaluation of nursery potting media combinations on germination, seedling growth and establishment of mango cultivars in the study area. Therefore, the experiment was aimed at evaluating germination and seedling growth response of mango root stock cultivars to different potting media combinations and identifying the best combinations of cultivar and potting medium that had good germination and growth performance.

Description of the study area
The experiment was conducted from April to September 2018 at a net-house in Indaselassie (ATVET) College farm, Northwestern zone of Tigray region, Ethiopia. The area is located at about "300 km" from Mekelle city which is the capital of the region. The site is located at 130 88′36″ to 140 08′ 57″ N latitude and 380 04′30″ to 380 17′ 02″ E longitudes at an altitude of 1915 m above sea level [13].
According to the agro-climatic classifications of Ethiopia, the climatic zone of the study area is generally subtropical with an extended dry period of 9-10 months. A maximum effective rainy season of 50-60 days with average annual rainfall of 885 mm which varies between 758 and 1440 mm. The area has average temperature of 20.92 °C with a mean maximum temperature of 30.97 °C in April and minimum temperature of 11.4 °C in January [13]. The soil type of the district is sandy clay loam with pH of 6.57 [14]. The major crops grown include are Onion, Tomato, Teff, Maize, Sorghum, and Finger millet [13] (Fig.1). In the experiment, local mango cultivar together with full top soil was used as a control treatment as the top soil was considered to possess poor physical properties such as poor aeration, water holding capacity etc. compared to those treatments having FYM(Farmyard manure), sawdust and sand. The total area of the experimental was 70 m 2 (4 m by 17.5 m).

Experimental procedure
Fresh mango fruits of three cultivars were gathered in consultation with experts from the district office of agriculture and rural development. About 360 healthy and mature mango fruits of each of the cultivars were selected from and taken to Indaselassie ATVET College nursery site. Immediately, freshly extracted seeds were cleaned with tap water then the healthy seeds within the same weight range were selected. The sowing of each cultivar seeds were done on the same day in the four different growing media combinations. One treatment within a block occupies 30 seedlings. Pot mixtures were prepared as per the ratio determined consisting of sand, soil, FYM and sawdust. FYM was obtained from dairy farm of Indaselassie Agricultural, Technical, Vocational, Educational and Training College. It was produced in a pit underneath shade to keep away from loss of nutrients through evaporation. The FYM was decomposed for about 6 months. Bi-product of Cordia africana wood saw-dust was collected from house furniture manufactures in Indaselassie town. Sand was collected from the upper river basin of the surrounding area. All media used for growing the seedlings were once sieved through mesh screen to obtain 1 mm to 5 mm ranged particles.
Physico-chemical properties of the nursery potting media were carried out. Media containing organic manures possess more available moisture or water holding capacity and some acids [15]. The seeds were sown at the depth of 2 cm in the media filled on black color polythene bags of 15 cm × 25 cm size [15]. Seeds were irrigated immediately after sowing and irrigation was continued every 2 days until the seeds start to germinate [16]. After start of germination, the seedlings were irrigated twice a week and allowed to grow for 120 days in the nursery. Moreover, simple shade structure was constructed using wood poles to support a roof of mesh wire upon which a thin layer of thatching grass to give protection against strong sunlight. Media were exposed to temperature/heat treatments to avoid nematode, insects and pathogens by putting 20 cm layer of media separately under a thin black plastic under the sun for a consecutive 3 days.

Data collection
Number of days for seed emergence: was recorded by counting the number of days taken from sowing till 50% of the seeds per plot start to emerge.
Germination percentage (%): The percentage of seeds germinated per plot was calculated by dividing number of germinating seedlings to total number of seeds and expressed in percent. Plant height (cm): Ten seedlings were randomly selected from each plot and plant heights were measured from the base to the tip of the shoot using a meter scale at 120 days after sowing seeds and the average height of ten plants were used for statistical analysis.
Number of leaves per plant: Numbers of leaves were recorded by counting leaves of ten randomly selected seedlings at 120 days after seeding and the average number of leaves were used for statistical analysis.
Number of stems per plant: Numbers of shoots per plant were counted at completion of germination from the ten randomly selected seedlings 120 days after planting and the average value was used for statistical analysis.
Internode length (cm): Internode length was recorded from all ten randomly selected seedlings using meter scale at 120 days after planting from node to another node of a seedling and it was summed up and the average of ten seedlings were used for statistical analysis.
Stem diameter (cm): Stem diameter was measured using digital caliper from ten randomly selected seedlings 120 days after sowing and their average value was used for statistical analysis.
Leaf area (cm): The leaf area was measured from ten randomly selected seedlings using meter scale at 120 days after seeding the seeds and computed using the formula developed by [17]: where, LA = Leaf area, W = width, L = Length, N = number of leaves.
Number of roots per plant: Numbers of roots were measured by counting the number of roots (tap and fibrous) from ten randomly selected seedlings at 120 days after sowing and the average was used for analysis.
Length of primary root (cm): Length of tap root was measured using a ruler at the end of 120 days after sowing from ten randomly selected seedlings of each plot which were carefully removed by cutting the polythene bags of seedlings and removing soil adhering to the roots of the seedlings.
Fresh weight of seedlings (g): Fresh weight of the whole parts of seedling (roots and shoots) was measured by weighing the weight of ten randomly selected seedlings per plot using sensitive balance at the end of the study period, 120 days after planting.
Dry weight (g): Dry weight of the whole parts of seedling was measured by drying ten randomly selected seedlings in an oven at 72 °C for 48 h [18] and dry biomass was weighted using sensitive balance and the average was used for statistical analysis.
Seedling vigour: Was determined according to the formula of [19];

Media analysis
Top soil samples collected from a depth of 0-30 cm were taken before the implementation of the experiment. The collected samples were air dried, mixed and ground to pass through 2 mm sieve to remove large particles, debris, and stones. Then, the samples were taken to Mekelle soil testing laboratory. Particle size distribution was analyzed using hydrometer procedure [20]. The pH of the soil was measured in water at soil to water ratio of 1:2.5 using pH meter [21]. Organic carbon was determined using wet oxidation method [22]. Total nitrogen was analyzed by wet oxidation procedure of Kjeldahl method [23]. Available phosphorus was analyzed using the procedure of [24]. Cation exchange capacity (CEC) was analyzed using NH 4 acetate method [25]. Farmyard manure and saw dust were also analyzed for the different parameters considered.

Data analysis
Collected data were subjected to Analysis of Variance (ANOVA) using standard procedure [26]. Fisher's LSD test at 5% probability level was used to separate the means. Pearson's correlation was done to examine the degree of association among the different parameters. Data analysis carried out using GenStat discovery 16th edition statistical software.

Results and discussion
Characteristics of the experimental nursery potting media Table 1 highlighted the characteristics of the experimental nursery soil, FYM and sawdust before planting. The textural class of the experimental soil was sandy clay loam having pH of 6.8 and classified as neutral as per the ratings of Horneck et al. [27]. The total nitrogen (N) content of the soil was 0.30%, which was high based on the rating of Hart et al. [28] which is in contrary to the reports where the soil of the study area are characterized with poor in fertility [29,30]. Available phosphorus (P) content was 6.10 ppm which is low as per the ratings of Olsen [24] which is similar with the reports where soils of the study area are poor Vigorindex(VI) − I(cm) = Mean seedling length × percent germination Vigorindex(VI) − II(g) = Dry weight of seedling × percent germination soil fertility [29,30]. Moreover, the available potassium (K) content of the experimental soil found to be 193 ppm which is rated as medium based on the ratings of Khan et al. [31] and is in line with the existing notion that Ethiopian soils are rich in potassium [32]. The cation exchange capacity was 49.57 meq/100 g of soil which is rated high based on the ratings of Hazelton and Murphy [33] and the organic carbon content was 1.08%, which is deficient according to Maria and Yost [34]. Generally, it is reported that soils in Tigray region where the study area is located, are characterized to be shallow, low in fertility, with high run-off, and low infiltration capacity which is attributed to high nutrient losses through soil erosion, and extremely low use of external nutrient inputs [29,30].
Except organic carbon, EC and available phosphorus of the experimental soil are suitable for the growth and development of mango seedlings. The addition of well decomposed FYM and sawdust can improve soil physical properties and there by enhance root development of mango seedling through improved aeration [31,35].
Similarly, Usman et al. [36] suggested on the use and positive of organic input on citrus seedlings. Therefore, soil fertility management in the study should focus on conditions that improve soil organic carbon and potassium through application of optimum levels of organic manure which thus improve soil physico-chemical properties [35].

Days to germination
Days to germination had significantly affected by the main effect of cultivar and its interaction of growth media while main effect of growing media did not Table 2 [37] reported similar findings where a combination of Soil: FYM: Sand (2:1:1) soil media with Master royal local cultivar of mango which resulted in early days to germination of 24.0 days. Moreover, Abdul [38] indicated similar findings. The probable reason for such findings in mango could be due to genetic differences and different media compositions [19,39].

Germination percentage
Main effect of cultivar and soil medium as well as their interactions had significantly (P ≤ 0.05) affected germination percentage of mango seedlings ( Table 2). Germination percentage was highest (97.8%) at the treatment combinations of local mango cultivar with full top-soil and is statistically at par with local mango cultivar in combination with top soil: FYM: sand (3:2:1). However, treatment combinations of Keitt cultivar and soil media composition of Top Soil: Sawdust: Sand (3:2:1) gave minimum (51.13) percent germination ( Table 2). In contrary, Parasana et al. [37] indicated highest germination percent of 81% at treatment combination of Master royal mango stone cultivar together with top soil: sand: FYM (2:1:1). Genetic variation, content of cotyledons /endosperm weight and hard nature of seed coat might affect the percent germination of mango. Many researchers reported varietal difference on seedling performance of mango [19,39,40].

Plant height
There was a significant difference in plant height of mango seedlings due to cultivar, soil media and their interactions (Table 3) (Table 3) 1:1). This could be due to the nutrient supply of the different combinations of soil potting media which might have helped in improving the rooting zone soil physico-chemical properties and thus increased nutrient assimilation initiate cell division, differentiation and enhanced nutrient availability leading to higher production of photo synthetically functional leaves and growth of plant [19,41].

Number of leaves
Number of leaves had significantly (P ≤ 0.05) affected by the main effect of cultivar, soil potting media as well as their interaction effects (Table 3) (Table 3). Master-royal mango cultivar in combination with soil potting media of composition of Soil: Sand: FYM (2:1:1) resulted in higher number of leaves [37]. Many researchers reported similar findings on different mango cultivars [17,42,43]. High soil nutrient availability in the potting media can improve nutrient availability and water for growth of mango seedlings [31].

Leaf area
Cultivar, soil potting media and their interactions had significantly (P ≤ 0.05) affected leaf area of mango seedlings (Table 3). Maximum leaf area of 86.68 cm was observed at the treatment combinations of soil media with compositions of Top soil: FYM: Sand (3:2:1) and local cultivar. However, the minimum leaf area of 23.11 cm was observed at combinations of Keitt cultivar together with soil media of composition of Top soil: Sawdust: Sand (3:2:1) ( Table 3). Abbas et al. [44] reported similar findings where combination of soil media with a composition of sand: peat moss: vermiculite (1:2:1) and local cultivar of mango gave the highest leaf area of 101.56 cm 2 . Better nutrient availability might led to improved production of functional leaves [37].

Stem diameter
Mango cultivar showed significant difference on stem diameter while, main effect of soil media and its interaction with cultivar did not (Table 3). Maximum stem diameter of 0.75 cm was obtained at combinations of soil media composition with Soil: FYM: Sand (3:2:1) and local cultivar while combinations of soil media with compositions of Top soil: FYM: Sawdust (3:2:1) and Keitt cultivar gave the minimum stem diameter of 0.44 cm (Table 3).
In line with the findings, maximum stem diameter of 0.79 cm was reported at 120 days after germination at combinations of Nekkare mango cultivar and soil media of composition of Soil: Sand: Compost: Coir pith (1:1:1:1) [38]. Moreover, Parasana et al. [37] indicated maximum stem diameter at combinations of Master royal cultivar of mango and soil media composition of Soil: Sand: FYM (2:1:1) at 180 days of germination. Difference in mango rootstock performance might have resulted in differences stem diameter characteristics [45,46].

Internode length
Local cultivar of mango gave longer internode length of 7.48 cm while Keitt cultivar gave the shortest with 3.63 cm. Moreover, full top soil gave longer internodes length of 6.84 cm while soil media composition of Top soil: Sawdust: Sand (3:2:1) gave the shortest with 4.15 cm (Table 4). However, there was no significant interaction effect of cultivar and growth media (Table 4). Higher (10.38 cm) internode length of mango seedlings were reported at soil media composition of Soil: Sand: Compost: Coir pith (1:1:1:1) with Neelum mango cultivar [38]. The relationship of media with seedling cultivar demonstrate massive growth in all vital plant growth parameters including, net plant growth, stem diameter, internode distance, number and size of leaves, root length and number of roots [36].

Stem number
Higher shoot number of 2.33 was observed at local mango cultivar while the lowest number of 1.  Table 4). The variation in stem number among mango seedlings could be due to seed polyembryonic nature that contains several embryos produced by nuclear embryos which grow to numerous plants commercially grown as cultivars [47].

Root number
Root number of mango seedlings had significantly affected by main effect of cultivar and its interaction with potting media while soil media did not (Table 5). Local     [38]. The findings obtained at the current study might be due to the desirable effects of media combinations on retaining regular moisture supply, root respiration and encouraging growth of mango seedling [50].

Biomass
Main effect of cultivar and potting media as well as their interaction effects significantly (P < 0.05) affected fresh and dry biomass of mango seedlings (Table 5). Maximum fresh and dry weight of 52.75 g and 22.35 g were observed at a combinations of local mango cultivar together with soil potting media of Soil: FYM: Sand (3:2:1) while the minimum fresh and dry weight of 9.57 g and 3.84 g, respectively, were obtained at combinations of Keitt cultivar and soil potting media of Top soil: FYM: Sawdust (3:2:1) ( Table 5). Maximum fresh weight was reported at combinations of mango Master-royal cultivar and soil media compositions of Soil: Sand: FYM (2:1:1) at 180 days after germination [37]. Similarly, soil media combinations of Top soil: FYM: leaf mould (1:1:1) and local cultivar gave the highest (41.83 g) fresh weight at 90 days after germination mango [35]. Moreover, it was reported that the highest dry weight of 31.25 g was observed with combinations of soil media compositions of Soil: Sand: FYM (1:1:1) and Dusehri cultivar of mango [49]. In conformity, maximum dry weight of 23.23 g of mango seedlings were observed with combinations of soil media of Soil: Sand: FYM (2: 1: 1) and Master-royal cultivar at 180 days after germination of seeds [37]. Meena et al. [51] indicated that the positive effect proper media composition on soil physico-chemical properties might be due to increased dry biomass of the seedlings.   (Table 6). Bappakka mango cultivar in combination with soil media composition of Sand: Red earth: FYM gave the highest vigor index [19]. Moreover, hormone GA 3 -100 ppm in combination with Varikka mango cultivar gave higher vigour index (VI)-I and II of 36.37 cm and 22.99 g, respectively [52]. The difference might be due to poorness or richness of the soil potting media and weight of seeds. Many investigators suggested more favorable media containing organic manures possess organic acid that might help in making available moisture and some acids might have helped in yielding minimum days and better germination percentage and particularly good root system development [37].