EFFECT OF THE SYMBIOTIC ENDOMYCORRHIZAE ON THE REPRODUCTIVE YIELD

AND DEVELOPMENT OF RAPID GROWTH RADISH BRASSICA RAPA

By Paulina Martin

(1152 Honors Biology)

ABSTRACT

It is not a coincidence that symbiotic associations between mycorrhizae fungi and plants

are present in 80% of land plants (Klironomos et al. 2000). Despite its benefits, environmental

factors can shift the plant-mycorrhizal balance from positive, to neutral or even negative

(Ronsheim 2012). The objective for the present investigation is to determine whether the

symbiotic association created between arbuscular mycorrhizae and Brassica rapa has

advantageous, neutral or disadvantageous effects for the plant. Based on literature findings, a

prior prediction is that mycorrhizae will have a beneficial effect on Brassica rapa, promoting

plant growth, rapid development, and reproductive yield. After experimentation and data

analysis, it was concluded that the symbiotic association between endomycorrhizae and Brassica

rapa plants had beneficial effects on the reproductive yield of plants, but neutral effects on the

germination of seeds of the plants. This reasoning was supported by the obtained results, which

demonstrated that the treatment group had a greater number of plants flowering, of plants

initiating pods and of flowers per plant, than the control group. Furthermore, it was also

concluded that mycorrhizae had neutral effects on seed germination of Brassica rapa, since the

number of seed germinating was similar between the treatment and the control plants.

INTRODUCTION

It is not a coincidence that symbiotic associations between mycorrhizae fungi and plants are

present in 80% of land plants (Klironomos et. Al. 2000). While the plant supplies the fungus

with carbon, the fungal contribution is more complex because it assists the plant with the

acquisition of immobile nutrients (Harrison 1996). Endomycorrhizae or arbuscular mycorrhizae

forms specialized structures called external fungal hyphae and internal arbuscules (Harrison

1996), which enhances the uptake of macronutrients such as a phosphorus, nitrogen, potassium

(Ramos-Zapata et al 2009; Pendleton 2002; Campbell 2013), micronutrients such as calcium,

magnesium, zinc (Ostar and Apkinar 2011; Madejon et al 2009; Shamsra et al 2012 ;), and water

(Pendleton 2002). Moreover, mycorrhizae has the ability to change the populations of

microorganism from the soil like nitrogen fixing bacteria, affecting this way the growth of plants.

In addition to this, mycorrhizae provides protection, improving the plant resistance to diseases

(Saia et al 2014), droughts, soil pollution (Hodge 2002), biotic and abiotic stresses (Saia et. Al.

2014), and gravity damages (Zachee et. al. 2008). For these reasons, it is reasonable to think that

endomycorrhizae play an important role in ecosystems (Riling 2004), thus representing two

thirds of all the symbiotic associations between fungi and plants (Hodge 2002).

Despite its benefits, environmental factors can shift the plant-mycorrhizal balance from

positive, to neutral or even negative (Ronsheim 2012). Thus, the objective for the present

investigation is to determine whether the symbiotic association created between arbuscular

mycorrhizae and Brassica rapa has advantageous, neutral or disadvantageous effects on the

number of germinating plants, number of flowering plants, number of producing pods, and the

number of flowers produced per plant (flower count/ flowering plants). Based on literature

findings, a prior prediction is that mycorrhizae will have a beneficial effect on Brassica rapa,

promoting plant growth, rapid development, and reproductive yield.

METHODS

The experiment was conducted under greenhouse conditions at College of DuPage, Glen

Ellyn, Illinois. From January 21st, 2015 to March 3rd, 2015, (41 days), the plant samples were

exposed to a photoperiod typical to Northern Illinois during January and maintained to the

constant temperature of 20°C.

In order to eliminate foreign organisms such as bacteria, two litters of Moisture Control

Potting Mix soil®, (Miracle-Gro Lawn Company), were cook at 148.889°C for six hours.

Subsequently, thirty plastic cups with small holes on the base were filled with 50 ml. of the cook

soil. Afterwards, three Brassica rapa seeds were sown inside each one of the thirty cups. Because

the experiment was conducted to test the effect of mycorrhizae on plants, the samples were

separated into two groups, each one with fifteen replicates: the control group and the treatment

group. After labeling the replicates with a “T” for treatment, or a “C” for Control, each group

was positioned inside a plastic tray. Moreover, 10 ml. of GLOMYGEL® mycorrhizal inoculum

(MYCOVITRO S.L., Granada, Spain), and 1 L. of distilled water were combined to create a

solution. The previous solution was spread among the treatment group (67 ml. per plant).

Additionally, water was added to the control group.

Once a week, tap water was added to the trays, so that the plants could absorb the ideal

amount of water. Throughout the experiment, four parameters were measured: number of

germinating plants, number of flowering plants, number of plants producing pods, and the

number of flowers per plant. These measurements were taken on February 11 (Day 20), February

18 (Day 27), February 27 (Day 34), and March 4 (Day 41).

Finally, after the experiment finished, the Chi-square test and the T-test were used to

analyze the obtained data: (1) The Chi-square goodness of fit test was used to test for differences

in counts of seeds germinating, plants flowering, and plants initiating pods between treatments;

(2) A one-tailed t-test was used to test if the mycorrhizal treatment showed a higher mean

flowering count/flowering plant.

RESULTS

Table No. 1 summarizes the number of germinating plants, flowering plants, and plants

initiating pods. The Chi-square test was applied to each one of these parameters.

Number of seeds germinating. - The amount of seeds germinating was measured on days

20, 27 and 41. The Chi-square value obtained for day 20 (7.08, P < 0.05) suggests that the

number of seeds germinating differs between the control (6 seeds germinating) and the treatment

(13 seeds germinating) replicates. Similarly, the Chi-squared value for day 27 (5.18, P < 0.05)

shows that the total number of germinating seeds is significantly different between the control

group (14 seeds germinating) and the treatments group (23 seeds germinating). In contrast, the

Chi-square value calculated for day 41(1.08) indicates that the total amount of germinating seeds

are similar in both the control (19 seeds germinating) and the treatment (24 seeds germinating)

replicates.

Number of plants flowering. - The number of plants flowering per group was measured

on days 34 and 41. After analyzing the calculated Chi-squared value for day 34 (3.12, P < 0.05),

it can be inferred that the number of plants flowering is similar between both groups (4 plants

flowering for the control replicates and 8 plants flowering for the treatment replicates). However,

the obtained Chi-squared value for day 34 (5.31, P < 0.05) indicates that the number of flowers is

significantly greater in the treatment group (15 flowering plants) than in the control group (8

plants flowering).

Number of plants initiating pods. - This parameter was measured only on day 41. The

Chi-square value obtained for this measurement (15.25, P < 0.05) shows that there is a

substantial difference in the amount of plants initiating pods between the control group (2 plants)

and the treatment group (8 plants).

Besides the number of germinating plants, flowering plants, and plants initiating pods,

the mean value of flowers per plant/mean value of flowering plants was also examined using the

T-test. The mean value for flower count/mean value of plants flowering ± standard deviation are

shown on Table No. 2.

Mean value for flower count/mean value of plants flowering.- Once the t o value was

calculated, the t o and the t c were compared so as to know if there was a difference between

flower count/ flowering plants between the treatment and the control plants. Since

t o>t c (3.165>1.721 ), it can be inferred that mean flower count/flowering plant was significantly

higher among plants in the mycorrhizal treatment (20.1 + 9.82; 15), than among control pants

(8.5 + 4.17; 8).

DISCUSSION

Number of seeds germinating. –even though the amount of seeds germinating for the

treatment group was greater than for the control group during the first 27 days, on day 41, the

numbers of seeds between both groups was similar. According to these data and the Chi-squared

test, it can be inferred that the symbiotic relationship between Brassica rapa and the arbuscular

mycorrhizae is only beneficial during the first stage of development. Once all the fifteen plants

form the treatment group germinated, it was only about time for the plants from the control

group to germinate; thus, the mycorrhizal association was neutral at this point, and therefore

there was not a difference in seeds germinating after 41 days. This growth depression is probably

caused because the cost of the carbohydrate drain by the endomycorrhizal fungus may be grater

that the benefit received by the plant (Ronsheim 2012).

Similar results were obtained by Pendleton (2000) where the treatment plants grew best

during the first year, but by the end of the second year the treatment had no significant effect.

Number of plants flowering. - The obtained data reveals that after 41 days, the amount of

plants flowering was substantially greater on the treatment replicates than in the control

replicates. These results suggest that the symbiotic association between Brassica rapa and

arbuscular mycorrhizae has a beneficial effect on the production of flowers, probably because

mycorrhizae improves the uptake of nutrients responsible for plant flowering and reproductive

success such as nitrogen and phosphorus (Poulton et al 1993; Ramos-Zapata et. Al. 2009). The

result for the present study agree with Pendleton (2002), who found that treatment plants had end

to have an earlier flowering, prolonged. Additionally, Shamshiri et al (2011) conclude that the

reproductive growth of mycorrhizal Kinnow and soybean plants was affected to some extent due

to an increase in flower production.

Number of plants initiating pods.- Since there is a substantial difference in the amount of

plants initiating pods between the control group and the treatment group, it is concluded that

mycorrhizal symbiosis was an advantaged for early pod development of Brassica rapa plants.

Similar conclusions that support the present research were obtained in other

investigations in which mycorrhizal associations showed to increase flower bud production in

pepper (Shamshiri et. Al 2012). Other researchers like Zachee eta al (2008) stated in their

investigation that the data obtained suggested an increase in yield per hectare of about 628% for

mycorrhizal plants compared to control, conforming the results of Betsama (1999). In addition to

this, Pendleton (2002) also noted that mycorrhizal symbiosis augmented the production of seeds

and the number of flower buds, and also enhanced growth and female reproductive output.

Mean value for flower count/mean value of plants flowering.- Because the mean flower

count/flowering plant was significantly higher among plants in the mycorrhizal treatment than

among control pants, on average, there was a greater amount of flowers among the treatment

group. Thus, it is reasonable to say that the mycorrhizal association had a beneficial effect on

treatment replications of Brassica rapa, causing a greater production of flowers per plant. A

greater amount of flowers per plant could be explained by the ability of mycorrhizal plants to

allocate less resources to root and more nutrients to reproductive yield (Rosenheim 2012). The

result for the present study agree with Pendleton (2002), who found that treatment plants had a

threefold increase of male flowers over control plants. Pendleton also noted that mycorrhizal

symbiosis augmented the number of inflorescences. Similarly, Scagel and Schreiner (2006)

concluded that arbuscular mycorrhizae treatment increased the flower production of petunia,

spotted snapweed and Chinese aster. Moreover, Rosenheim (2012) stated that the presence of

mycorrhizae in plant resulted in larger bulbs and a greater amount of flowers per plant.

In conclusion, after analyzing the obtained data (Table No. 1 and Table No. 2) and

evaluating the proposed hypothesis, it is reasonable to state that the symbiotic association

between endomycorrhizae and Brassica rapa plants had beneficial effects on the reproductive

yield of plants, but neutral effects on the germination of seeds of the plants. Recall from the

results that the treatment group had a greater number of plants flowering, of plants initiating pods

and of flowers per plant, than the control group. Furthermore, it was also concluded that

mycorrhizae has neutral effect of seed germination of Brassica rapa, since the number of seed

germinating was similar between the treatment and the control replicates.

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2827.

Table No. 1 summarizes the number of germinating plants, flowering plants, and plants

initiating pods. The Chi-square test was applied to each one of these parameters.

Day of the experiment

Treatment

Control Mycorrhizae

Seeds germinating20 6 13 *7.0827 14 23 *5.1841 19 24 1.08

Plants flowering34 4 8 *3.1241 8 15 *5.31

Plants initiating pods41 2 8 *15.25

Note: * denotes significant (P<0.05).

Table No. 2 shows the mean value for flower count/mean value of plants flowering ± standard deviation.

Treatment Flower count/flowering plantControl 8.5 + 4.17; 8

Mycorrhizae 20.1 + 9.82; 15