**3. Results**

Mexico [8]. Sampling was carried out in 10% of the total cultivated area of nine municipalities of Sonora state (Agua Prieta, Caborca, Cajeme, Hermosillo, Moctezuma, Navojoa, Sahuaripa, Santa Ana, and Ures). Located in the geographical coordinates, Agua Prieta 31° 17′ north latitude and 109° 33′ west longitude, Caborca 30° 42′ north latitude and 112° 09′ longitude west, Cajeme 27° 29′ north latitude and 109° 56′ longitude west, Hermosillo 29° 05′ north latitude and 110° 57′ longitude west, Moctezuma 29° 47′ north latitude and 109° 40′ west longitude, Navojoa 27° 03′ north latitude and 109° 25′ west longitude, Sahuaripa 29° 03′ north latitude and 109° 14′ west longitude, Santa Ana 30° 33′ north latitude and 111° 07′ west longitude, and Ures 29° 25′ north latitude and 110° 23′ west longitude. In the 10% of the surface of each municipality, the following was done: each batch of 5 ha was considered as a sampling area. Each hectare of that surface was a must-see. At each point an imaginary diagonal line was drawn from corner to corner, and on that straight line, ten samples were collected. Donations from producers were obtained. Each of the collected samples, previously identified, was wrapped

with wet paper and placed in a cooler to be transferred to the laboratory for analysis.

described in the detection of the microorganism in the PP was considered.

reaffirm the null or positive presence.

128 Potato - From Incas to All Over the World

**thyme against** *Ralstonia solanacearum*

Detection of Rs in tuber. According to Rueda [1], each tuber sample, consisting of 10 tubers from each batch of cooperating producers, weighed separately, washed in running water for 30 min, and placed in plastic trays with a capacity of 2 L. Each tray, with its respective sample of tuber, is left with an amount of 100 ml of distilled water, and each of these trays was added 2 ml of buffer solution phosphatase with a pH = 7. The water-phosphatase mixture containing each tuber sample is called a "mother suspension." The trays were incubated for 12 hours in cooling at 4°C in order to release the bacteria to the stock suspension. After the incubation, 10 ml was taken from suspension of each of the trays, four dilutions were made to such suspension (10:1, 10:2, 10:3, 10:4), and the last dilution of 0.1 ml was taken and sowed in specific culture medium in Petri dishes by the rod dispersion method The media were incubated for 7 days at 34°C. The inoculated media were then incubated at a temperature of 35°C for 7 days [1]. Detection of Rs in vegatitive material sampled (tuber, sedling, leaf and fruit), by ELISA technique. For the detection of *Rs*, with respect to the serological ELISA technique, the protocol

Detection of *Rs* in tuber, seedling, leaf developed and fruit by PCR technique. Commercial primers were obtained from the 16Sr intergenic region, and screening tests were performed to

Pathogenicity tests to positive bacteria with the different methods of detection. For the reaffirmation of *Rs* bacteria that proved to be positive in previous detection methods, they were carrying out pathogenicity tests [5]. The PPs were applied to seedlings 25–30 days after emergence, as described above in the PP of the first stage. The diseased tissue bacteria were rein-

This stage which consisted of the evaluation of the antibacterial activity of two essential oils was carried out in the laboratory microbiology and mycotoxins of the Department of

oculated using the Randhawa technique, and the pathogen was confirmed by ELISA.

**2.2. Evaluation of the in vitro antibacterial activity of essential oils of oregano and** 

#### **3.1. Detection of brown rot (***Ralstonia solanacearum***) of potato crop (***Solanum tuberosum* **L.) of the state of Sonora (Mexico)**

#### *3.1.1. First stage*

When testing for pathogenicity for *R. solanacearum* (*Rs*) symptoms in potato seedlings, the results indicate that between the tubers embedded in the bacterial suspension of 108 CFU/ml and between 7 and 15 days under favorable conditions of the disease, the vascular bundle of the tuber was darkened, and, when making a cross section, a grayish bacterial mucilage was exuded by the eyes and by the end of the stolon in the tubers. There were grayish-white outcrops that exudate from the darkened vascular ring of the cut tubers. On the other hand, in the inoculated seedlings when making a transverse cut at the stem level, the exudation of a graybrown mucilage was noted. This could be verified by makng a transverse cut at the base of the stem of the seedling and observing a milky-white filamentous fluid emanating from the vascular bundles and submerging a piece of the stem in clean, sterile water. In the same way, in the first true leaves for the seedling case, irregular spots of whitish appearance were observed in relation to the healthy area, and finally the death of the seedling occurred. For this, first appeared irregular spots at first clear and then obscure, and after 7–14 days death occurred. An opposite result was for those PPs that were directed as negative control by the use of sterile distilled water, in tuber-tubercle and seedling, being observed that the organs used were shown healthy, except in tuber where the punctured area showed a light brown oxidation (2 mm) which, when pressed, showed the same solid consistency as the healthy area [7].

Regarding the sowing of "bacterial suspensions" obtained from the pathogenicity test on media Mannitol salt agar (SMSA), and tetrazolium chloride (TZC) cultures, the results indicate that on the TZC medium, developed colonies showed a pinkish-white color, while on the SMSA medium, colonies of developed bacteria showed an irregular shape, of white color and with centers of pink color after 72 hours of incubation at 30°C. A similar result was obtained for those PPs that were inoculated with the positive control (*Rs*), whereas for those samples generated from the PPs that served as negative control (sterile distilled water), the results on both media used were non-mucoid dry colonies [7].

By ELISA confirmation, a positive result was obtained for the control strain (*Rs*), as well as for the bacterial suspensions isolated from the aforementioned pathogenicity tests and from those grown on the culture media SMSA and TZC. The opposite happened with the negative control [7].

> obtained from the municipalities of Agua Prieta, Navojoa, Hermosillo, and Caborca, they were negative when using specific media (SMSA and TZC) and serological tests, except in the

> **Table 1.** Surface sowed by potato crop in different districts of Sonora state (surface sampled to detect *Ralstonia*

**Total Irrigation Raining area Surface sampled from** 

*Ralstonia solanacearum*: A Bacterial Disease and Its Biological Control by Essential Oils on *Solanum tuberosum* L.

Navojoa 3940 3940 0 394 0 Cajeme 2406 2406 0 240.6 0 Hermosillo 371 371 0 37.1 0 Ures 115 115 0 11.5 0 Caborca 2000 2000 0 200 0 Agua Prieta 35 35 0 3.5 0 Sahuaripa 5 0 5 0 0.5 Santa Ana 30 30 0 3 0 Moctezuma 1 1 0 0.1 0 Total 8903 8898 5 889.8 0.5

**irrigation area 10%**

**Surface sampled from** 

131

**raining area**

http://dx.doi.org/10.5772/intechopen.70744

On the other hand, when analyzing the vegetative samples from Sahuaripa, Cajeme, and Ures, the analyses showed negative results in specific medium SMSA and serological tests, the opposite occurred in culture medium TZC and PPO test. An additional test was developed to the isolated colonies of the different sampling points, resulting being Gram-negative, in a bar form, strictly aerobic, and with measurement of 0.3–0.5 × 1.0–1.5 μm. For the municipality of Moctezuma, the results indicate the negative presence of *Rs*. A favorable result was obtained for the positive control in the tests SMSA, TZC, PPO, and ELISA [7]. Concerning the PP of the positive samples of consuming tuber, tubers embedded in the bacterial suspension of 108 CFU/ml, between 5 and 15 days under favorable conditions of the disease, presented a wateriness in the vascular bundle of the tuber. It was also detected that in tubers inoculated with *Rs*, whitish exudates of paste consistency appeared. As the infection evolved, there was a darkening of the entire vascular ring, and the adjacent tissues began to decompose, presenting a yellowish, creamy, or brownish coloration, eventually ending up rotting. When corroborating these symptoms by the ELISA technique, the result was positive for *Rs*. In the case of seedlings, the pathogenicity tests showed, in the first true leaves, irregular spots of whitish appearance relative to the healthy area and finally the death of the seedling. For this, irregular, initially clear and subsequently obscure patches were first presented, slight yellowing of the bacterial wilt disease of the plant, which is observed first on a single side of the leaf or on a branch, and after 7–14 days, death occurred. A positive result for *Rs* was obtained by ELISA, when analyzing the organs of PP in the seedling stage. The opposite occurred for those PP

PPO test that was positive for leaf and fruit (**Table 3**) [7].

**District Area sowed (ha)**

*solanacearum*).

organs inoculated with sterile distilled water [7].

#### *3.1.2. Second stage*

Sampling of potatoes was carried out in the municipalities of Agua Prieta, Caborca, Cajeme, Hermosillo, Moctezuma, Navojoa, Sahuaripa, Santa Ana, and Ures according to the sampling method [8] and detection of *Rs* (**Table 1**). It indicates the surface that is directed to the production of potato in the state of Sonora. The sampled area (889.8) can be identified, with the municipality of Navojoa and Cajeme with 394 and 240.6 ha, respectively [7].

The results of the phytopathological diagnosis show positive *Rs* for the municipalities of Navojoa, Hermosillo, and Agua Prieta in a consumption tuber that can be used as seed (**Table 2**). When the tests were carried out on the SMSA, TZC, and PPO media, the results were positive since the visible colonies on SMSA medium were after 36–48 hours of growth at 30°C, white with pink to colored centers of cream and irregularly round; on the TZC medium, the colonies appeared white with pink centers. It is possible to indicate that those bacterial colonies grown on SMSA and TZC medium obtained from samples of potatoes for consumption indicated that the bacterial cells were Gram-negative, in a bar form, strictly aerobic, and with measurement of 0.5–0.7 × 1.5–2.0 μm. These colonies were tested positive by ELISA and PCR [7].

In import tuber, the results were negative. Nonetheless, it is important to note that in response from abroad, there was variability of response for the municipalities of Agua Prieta, Sahuaripa, Moctezuma, Hermosillo, and Ures, as they were positive with the specific medium TZC but negative to the PPO and ELISA test [7].

Regarding the analyses carried out in seedlings, a leaf developed during the flowering stage and tubercle of fruit sampled at physiological maturity, the results indicate that for samples *Ralstonia solanacearum*: A Bacterial Disease and Its Biological Control by Essential Oils on *Solanum tuberosum* L. http://dx.doi.org/10.5772/intechopen.70744 131


stem of the seedling and observing a milky-white filamentous fluid emanating from the vascular bundles and submerging a piece of the stem in clean, sterile water. In the same way, in the first true leaves for the seedling case, irregular spots of whitish appearance were observed in relation to the healthy area, and finally the death of the seedling occurred. For this, first appeared irregular spots at first clear and then obscure, and after 7–14 days death occurred. An opposite result was for those PPs that were directed as negative control by the use of sterile distilled water, in tuber-tubercle and seedling, being observed that the organs used were shown healthy, except in tuber where the punctured area showed a light brown oxidation (2 mm) which, when pressed, showed the same solid consistency as the healthy area [7].

Regarding the sowing of "bacterial suspensions" obtained from the pathogenicity test on media Mannitol salt agar (SMSA), and tetrazolium chloride (TZC) cultures, the results indicate that on the TZC medium, developed colonies showed a pinkish-white color, while on the SMSA medium, colonies of developed bacteria showed an irregular shape, of white color and with centers of pink color after 72 hours of incubation at 30°C. A similar result was obtained for those PPs that were inoculated with the positive control (*Rs*), whereas for those samples generated from the PPs that served as negative control (sterile distilled water), the results on both media

By ELISA confirmation, a positive result was obtained for the control strain (*Rs*), as well as for the bacterial suspensions isolated from the aforementioned pathogenicity tests and from those grown on the culture media SMSA and TZC. The opposite happened with the negative control [7].

Sampling of potatoes was carried out in the municipalities of Agua Prieta, Caborca, Cajeme, Hermosillo, Moctezuma, Navojoa, Sahuaripa, Santa Ana, and Ures according to the sampling method [8] and detection of *Rs* (**Table 1**). It indicates the surface that is directed to the production of potato in the state of Sonora. The sampled area (889.8) can be identified, with the

The results of the phytopathological diagnosis show positive *Rs* for the municipalities of Navojoa, Hermosillo, and Agua Prieta in a consumption tuber that can be used as seed (**Table 2**). When the tests were carried out on the SMSA, TZC, and PPO media, the results were positive since the visible colonies on SMSA medium were after 36–48 hours of growth at 30°C, white with pink to colored centers of cream and irregularly round; on the TZC medium, the colonies appeared white with pink centers. It is possible to indicate that those bacterial colonies grown on SMSA and TZC medium obtained from samples of potatoes for consumption indicated that the bacterial cells were Gram-negative, in a bar form, strictly aerobic, and with measurement of

In import tuber, the results were negative. Nonetheless, it is important to note that in response from abroad, there was variability of response for the municipalities of Agua Prieta, Sahuaripa, Moctezuma, Hermosillo, and Ures, as they were positive with the specific medium TZC but

Regarding the analyses carried out in seedlings, a leaf developed during the flowering stage and tubercle of fruit sampled at physiological maturity, the results indicate that for samples

municipality of Navojoa and Cajeme with 394 and 240.6 ha, respectively [7].

0.5–0.7 × 1.5–2.0 μm. These colonies were tested positive by ELISA and PCR [7].

used were non-mucoid dry colonies [7].

130 Potato - From Incas to All Over the World

negative to the PPO and ELISA test [7].

*3.1.2. Second stage*

**Table 1.** Surface sowed by potato crop in different districts of Sonora state (surface sampled to detect *Ralstonia solanacearum*).

obtained from the municipalities of Agua Prieta, Navojoa, Hermosillo, and Caborca, they were negative when using specific media (SMSA and TZC) and serological tests, except in the PPO test that was positive for leaf and fruit (**Table 3**) [7].

On the other hand, when analyzing the vegetative samples from Sahuaripa, Cajeme, and Ures, the analyses showed negative results in specific medium SMSA and serological tests, the opposite occurred in culture medium TZC and PPO test. An additional test was developed to the isolated colonies of the different sampling points, resulting being Gram-negative, in a bar form, strictly aerobic, and with measurement of 0.3–0.5 × 1.0–1.5 μm. For the municipality of Moctezuma, the results indicate the negative presence of *Rs*. A favorable result was obtained for the positive control in the tests SMSA, TZC, PPO, and ELISA [7]. Concerning the PP of the positive samples of consuming tuber, tubers embedded in the bacterial suspension of 108 CFU/ml, between 5 and 15 days under favorable conditions of the disease, presented a wateriness in the vascular bundle of the tuber. It was also detected that in tubers inoculated with *Rs*, whitish exudates of paste consistency appeared. As the infection evolved, there was a darkening of the entire vascular ring, and the adjacent tissues began to decompose, presenting a yellowish, creamy, or brownish coloration, eventually ending up rotting. When corroborating these symptoms by the ELISA technique, the result was positive for *Rs*. In the case of seedlings, the pathogenicity tests showed, in the first true leaves, irregular spots of whitish appearance relative to the healthy area and finally the death of the seedling. For this, irregular, initially clear and subsequently obscure patches were first presented, slight yellowing of the bacterial wilt disease of the plant, which is observed first on a single side of the leaf or on a branch, and after 7–14 days, death occurred. A positive result for *Rs* was obtained by ELISA, when analyzing the organs of PP in the seedling stage. The opposite occurred for those PP organs inoculated with sterile distilled water [7].


**Districts sampled Techniques of diagnosis**

− − −

− − −

− − −

− − −

− − −

− − −

− − −

− − −

− − −

Control positive *Rs* + + + + Control negative *Rs* − − − −

**Navojoa** Seedling Leaf Fruit

**Cajeme** Seedling Leaf Fruit

**Hermosillo** Seedling Leaf Fruit

**Ures** Seedling Leaf Fruit

**Caborca** Seedling Leaf Fruit

**Agua Prieta** Seedling Leaf Fruit

**Sahuaripa** Seedling Leaf Fruit

**Santa Ana** Seedling Leaf Fruit

**Moctezuma** Seedling Leaf Fruit

water.

(Mexico).

**Test SMSA Test TZC Test PPO Serology technique**

*Ralstonia solanacearum*: A Bacterial Disease and Its Biological Control by Essential Oils on *Solanum tuberosum* L.

− + +

+ + +

− + +

+ + +

− + +

− + +

+ + +

− − −

− − − − − −

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133

− − −

− − −

− − −

− − −

− − −

− − −

− − −

− − −

− − −

+ + +

− − −

+ + +

− − −

− − −

+ + +

− − −

− − −

+, Test positive; −, test negative; specific medium, SMSA and TZC. PPO, oxidase test; control negative = sterile distilled

**Table 3.** Detection of *Ralstonia solanacearum* in seedling, leaf, and fruit sampled from crop potato areas in Sonora

**Table 2.** Detection of *Ralstonia solanacearum* in potato tuber from Canada and the United States of America (USA) and tuber of potato sampled in commercial stores in Sonora state, which is for human consumption and used as a seed.

#### **3.2. Evaluation of the in vitro antibacterial activity of essential oils of oregano and thyme against** *Ralstonia solanacearum*

Both oregano and thyme essential oils presented inhibition halos, such as antimicrobial activity against *R. solanacearum*, at all concentrations and amounts applied.

*Ralstonia solanacearum*: A Bacterial Disease and Its Biological Control by Essential Oils on *Solanum tuberosum* L. http://dx.doi.org/10.5772/intechopen.70744 133


+, Test positive; −, test negative; specific medium, SMSA and TZC. PPO, oxidase test; control negative = sterile distilled water.

**3.2. Evaluation of the in vitro antibacterial activity of essential oils of oregano and thyme** 

**Table 2.** Detection of *Ralstonia solanacearum* in potato tuber from Canada and the United States of America (USA) and tuber of potato sampled in commercial stores in Sonora state, which is for human consumption and used as a seed.

+, Test positive; −, test negative; specific media, SMSA and TZC. *Rs*, *Ralstonia solanacearum*; PPO, oxidase test.

**Potato tuber's sampled in commercial stores in Sonora state, which is for human consumption and used as a seed**

Navojoa + + + + Cajeme − − − − Hermosillo + + + + Ures − − − − Caborca − − − − Agua Prieta + + + + Sahuaripa − − − − Santa Ana − − − − Moctezuma − − − − Control positivo *Rs* + + + + Control negativo (distilled water) − − − −

**Technical of diagnosis**

Navojoa − − − − Cajeme − − − − Hermosillo − + − − Ures − + − − Ures − + − − Caborca − − − − Agua Prieta − + − − Sahuaripa − + − − Santa Ana − − − − Moctezuma − + − −

**Test SMSA Test TZC Test PPO Serology technique**

Both oregano and thyme essential oils presented inhibition halos, such as antimicrobial

activity against *R. solanacearum*, at all concentrations and amounts applied.

**against** *Ralstonia solanacearum*

**Potato from Canada and the USA**

132 Potato - From Incas to All Over the World

**Table 3.** Detection of *Ralstonia solanacearum* in seedling, leaf, and fruit sampled from crop potato areas in Sonora (Mexico).

The average antibacterial activity obtained from all concentrations and different amounts of oregano extract applied was 25.8 mm. The mean inhibition values found were 38.3, 20.5, and 20.2 mm in diameter, for concentrations 1:1, 1:5, and 1:10, respectively. In a similar study in which the antibacterial activity of the oils of four different varieties was evaluated, oregano on *C. michiganensis* subsp. *michiganensis* (Cmm) bacteria average values of 47.5, 35.6, and 30.8 mm in diameter for the same concentrations and in the amount used applied 15 μl [6] were found. These inhibition results are greater than those found in the present experiment; this may be due not only to the different sensitivity of the bacteria under study but also to the different composition of the oregano oils used. The concentration of essential oil of oregano showed that the greater antibacterial activity against *R. solanacearum* was 1:1 in different amounts applied with 7.5 μl with 35.16, 10 μl with 39.15 mm, and 15 μl with 40.83 mm in diameter. On the other hand, the results of inhibition of *R. solanacearum* were very similar when they were applied with 7.5 and 10 μl of the extract in concentrations 1:5 (average value, 19 mm) and 1:5 (average value, 19.5 mm). However, the amount applied had the greatest effect when 15 μl of the extract was applied, especially in the 1:5 concentration (23.8 mm).

The average antibacterial activity obtained from all concentrations and different amounts of thyme extract evaluated was 26.2 mm. The mean inhibition values found were 36.3, 28.0, and 14.1 mm in diameter, for the concentrations 1.1, 1:5, and 1.10, respectively. Our results were lower compared with [6], which obtained 50.3, 33.0, and 21.0 mm for the same concentrations to *C. michiganensis* subsp. *michiganensis*.

The concentration of thyme oil that showed the greatest halo of growth inhibition of the bacterium *R. solanacearum* was the 1:1 concentration in the different amounts applied, with 33.5, 35.2, and 40.5 mm, when 7.5, 10, and 15 μl, respectively, as shown in **Figure 1(a)**.

When comparing the essential oils of oregano (*L. graveolens*) and thyme (*T. vulgaris* L.) with respect to mean halo values of inhibition in the growth of *R. solanacearum* (P > 0.05), there is no significant difference in oregano (25.907) and thyme (27,204). The two oils are considered to have an inhibitory effect on the growth of *R. solanacearum*. Other studies also showed inhibitory capacity in bacterias such as *Agrobacterium tumefaciens*, *C. michiganensis* subsp. *michiganensis*, *Erwinia amylovora*, *E. carotovorum*, *E. Xanthomonas vesicatoria* [9–11]. Regarding the comparison of the average values of the dilutions (1:1, 1:5, 1:10) of the essential oils of oregano and thyme in halo of inhibition of growth of *R. solanacearum* (**Figure 1(a, b)**), the resoults showed a significant difference (p0.05) in the 1:1 dilution. In addition a similar result with the 1:1 dilution was obtained in the growth inhibition study of *C. michiganensis* subsp. *michiganensis* with oregano and thyme oils [6].

In the comparison of the mean values of applied amounts (7.5, 10.15 μl) of oregano and thyme essential oils in growth inhibition halo of *R. solanacearum* (P < 0.05), there was a significant difference in applied amount of 15 μl:30, 7.5 μl:22.7, and 10 μl:26.05 (**Figure 1(a, b)**). The growth inhibition halo values of the bacterium *R. solanacearum* by the effect of oregano and thyme oils

are shown in **Table 4** in which it is indicated that (P > 0.05) there is no significant difference

**Figure 1.** Inhibition of growth of *Ralstonia solanacearum* by oils of oregano (a) and thyme (b) in dilutions of 1:1, 1:5, and

*Ralstonia solanacearum*: A Bacterial Disease and Its Biological Control by Essential Oils on *Solanum tuberosum* L.

http://dx.doi.org/10.5772/intechopen.70744

135

between oregano stockings 40,833 and thyme 40,500 ha.

1:10 at 7.5, 10, and 15 μl applied at 24 hours.

*Ralstonia solanacearum*: A Bacterial Disease and Its Biological Control by Essential Oils on *Solanum tuberosum* L. http://dx.doi.org/10.5772/intechopen.70744 135

The average antibacterial activity obtained from all concentrations and different amounts of oregano extract applied was 25.8 mm. The mean inhibition values found were 38.3, 20.5, and 20.2 mm in diameter, for concentrations 1:1, 1:5, and 1:10, respectively. In a similar study in which the antibacterial activity of the oils of four different varieties was evaluated, oregano on *C. michiganensis* subsp. *michiganensis* (Cmm) bacteria average values of 47.5, 35.6, and 30.8 mm in diameter for the same concentrations and in the amount used applied 15 μl [6] were found. These inhibition results are greater than those found in the present experiment; this may be due not only to the different sensitivity of the bacteria under study but also to the different composition of the oregano oils used. The concentration of essential oil of oregano showed that the greater antibacterial activity against *R. solanacearum* was 1:1 in different amounts applied with 7.5 μl with 35.16, 10 μl with 39.15 mm, and 15 μl with 40.83 mm in diameter. On the other hand, the results of inhibition of *R. solanacearum* were very similar when they were applied with 7.5 and 10 μl of the extract in concentrations 1:5 (average value, 19 mm) and 1:5 (average value, 19.5 mm). However, the amount applied had the greatest effect when 15 μl of the extract was applied, especially in the 1:5 concentration

The average antibacterial activity obtained from all concentrations and different amounts of thyme extract evaluated was 26.2 mm. The mean inhibition values found were 36.3, 28.0, and 14.1 mm in diameter, for the concentrations 1.1, 1:5, and 1.10, respectively. Our results were lower compared with [6], which obtained 50.3, 33.0, and 21.0 mm for the same concentrations

The concentration of thyme oil that showed the greatest halo of growth inhibition of the bacterium *R. solanacearum* was the 1:1 concentration in the different amounts applied, with 33.5, 35.2, and 40.5 mm, when 7.5, 10, and 15 μl, respectively, as shown in

When comparing the essential oils of oregano (*L. graveolens*) and thyme (*T. vulgaris* L.) with respect to mean halo values of inhibition in the growth of *R. solanacearum* (P > 0.05), there is no significant difference in oregano (25.907) and thyme (27,204). The two oils are considered to have an inhibitory effect on the growth of *R. solanacearum*. Other studies also showed inhibitory capacity in bacterias such as *Agrobacterium tumefaciens*, *C. michiganensis* subsp. *michiganensis*, *Erwinia amylovora*, *E. carotovorum*, *E. Xanthomonas vesicatoria* [9–11]. Regarding the comparison of the average values of the dilutions (1:1, 1:5, 1:10) of the essential oils of oregano and thyme in halo of inhibition of growth of *R. solanacearum* (**Figure 1(a, b)**), the resoults showed a significant difference (p0.05) in the 1:1 dilution. In addition a similar result with the 1:1 dilution was obtained in the growth inhibition study of *C. michiganensis* subsp. *michiganen-*

In the comparison of the mean values of applied amounts (7.5, 10.15 μl) of oregano and thyme essential oils in growth inhibition halo of *R. solanacearum* (P < 0.05), there was a significant difference in applied amount of 15 μl:30, 7.5 μl:22.7, and 10 μl:26.05 (**Figure 1(a, b)**). The growth inhibition halo values of the bacterium *R. solanacearum* by the effect of oregano and thyme oils

(23.8 mm).

134 Potato - From Incas to All Over the World

**Figure 1(a)**.

to *C. michiganensis* subsp. *michiganensis*.

*sis* with oregano and thyme oils [6].

**Figure 1.** Inhibition of growth of *Ralstonia solanacearum* by oils of oregano (a) and thyme (b) in dilutions of 1:1, 1:5, and 1:10 at 7.5, 10, and 15 μl applied at 24 hours.

are shown in **Table 4** in which it is indicated that (P > 0.05) there is no significant difference between oregano stockings 40,833 and thyme 40,500 ha.


According to the essential oils of oregano and thyme, they showed inhibitory effects on the growth of the bacterium *R. solanacearum* at the 1:1 dilution result (P < 0.05) to be more effective than the rest of the dilutions evaluated, and the most effective applied amount was 15 μl of

*Ralstonia solanacearum*: A Bacterial Disease and Its Biological Control by Essential Oils on *Solanum tuberosum* L.

The essential oils of oregano and thyme showed (P < 0.05) better inhibitory effect than the antibiotics used streptomycin (10 μg) and ampicillin. Therefore, essential oils are excellent alternatives to antibiotics in the control of the bacterium *R. solanacearum.* However, it is very important to consider others studies to evaluate the phytotoxic activity of essential oils studied in this research (*L. graveolens* and *T. vulgaris*) on *Rs* in different phenological stages of

and Edgar Omar Rueda Puente3

http://dx.doi.org/10.5772/intechopen.70744

\*

137

, Ramón Jaime Holguin Peña2

1 Universidad Autonoma de Baja California, Instituto de Ciencias Agrícolas, Méxicali,

2 Center for Biological Research of the Northwest, Instituto Politecnico Nacional 195,

[1] Rueda PEO. Producción de antisuero contra *Acidovorax avenae* pv*. citrulli* y su detección en la Comarca Lagunera. [thesis]. Saltillo, Coahuila, México: Universidad Autónoma

[2] SIAP (Servicio de Información Agroalimentaria y Pesquera). 2012. Available from: http://www.siap.go.mx/index.php?option=comwrapper&view=wrapper&itemid=351.

[3] Daferera DJ, Ziogas BN, Polissiou MG. The effectiveness of plant essential oils in the growth of *Botrytis cinerea*, Fusarium sp. and *Clavibacter michiganensis* subsp. *michiganen-*

[4] Ponce AG, del Valle C, Roura SI. Evaluation of plant essential oil as natural posharvest disease control of tomato (*Lycoperciom esculentum* L.). International Society Horticultural

[5] Randhawa P. Fruit Blotch Testing Protocol. Roseville, California, USA: Plant Lab; 1996. p. 110

3 Sonora University, Agriculture Department, Boulevard Luis Encinas y Rosales,

\*Address all correspondence to: erueda2@hotmail.com

Colonia Playa Palo de Santa Rita, La Paz, BCS, Mexico

Colonia Centro, Hermosillo, Son, Mexico

Agraria Antonio Narro; 1998

*sis*. Crop Protection. 2003;**22**:39-44

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oregano and thyme essential oil.

potato crop under production system.

**Author details**

Cristina Ruiz Alvarado1

Baja California, México

**References**

**Table 4.** Inhibition of growth of *Ralstonia solanacearum* by essential oils (trifactorial A × B × C).
