УДК 63

ИССЛЕДОВАНИЕ И СОПОСТАВКА АГРЕССИВНОСТИ ДВУХ ИЗОЛЯТОВ Р.ALTERNARIA К ТАБАКУ

Георгиева-Андреева Мариела1, Танова Красимира2
1Институт земледелия, г.Шумен, Болгария, научный сотрудник
2Шуменский Университет «Епископ Константин Преславски», Болгария, доцент

Аннотация
Было проведено перекрестное заражение листьев табака споровой суспензией патогена /гриба/ р. Аlternaria /1500 спор/1ml./, взятого с больных растений табака и стевии в лабораторных условиях. Результаты проведенного опыта показали, что табак может являться приемником патогенных грибов р.Alternaria, изолированных у стевии. Типы реакций на заражение потогенами, взятых с двух видов растений несколько отличаются. У варианта, зараженного изолятом со стевии, средний размер пятен меньше на 20% среднего диаметра пятен на листьях, зараженных изолятом с табака.
По отношению к степени нападения /агрессивности/ двух изолятов статистически значимой разницы не было отмечено.

Ключевые слова: алтернария, стевия, табак


EXAMINATION OF THE AGGRESSIVENESS OF TWO ISOLATES FROM THE ALTERNARIA GENUS IN TOBACCO

Georgieva-Andreeva Mariela1, Tanova Krasimira2
1Agricultural Institute, Shumen, Bulgaria, researcher
2Konstantin Preslavski University of Shumen, Bulgaria, Associate Professor

Abstract
We have carried out cross infection of tobacco leaves with spore suspension from genus Alternaria pathogens (1500 spores/lml) isolated from infected tobacco plants and infected stevia plants, in laboratory conditions. The results from the laboratory experiment show that tobacco can be a host of the pathogenic fungi of the Alternaria genus isolated from stevia. Both isolates differ in the way they react to the infection. In the samples infected with isolates from stevia the average diameter of the spots is 20% smaller than the average diameter of the spots on the leaves inoculated with tobacco isolates. Regarding the attack rate (0% colonized area), there is no significant difference statistically.

Keywords: Alternaria, stevia, tobacco


Рубрика: Сельское хозяйство

Библиографическая ссылка на статью:
Георгиева-Андреева М., Танова К. Examination of the Aggressiveness of Two Isolates from the Alternaria Genus in Tobacco // Сельское, лесное и водное хозяйство. 2014. № 5 [Электронный ресурс]. URL: http://agro.snauka.ru/2014/05/1467 (дата обращения: 30.04.2017).

The pathogenic fungi from Alternaria alternata can cause disease in more than 100 sorts of plants (Rotem, 1994; Kusaba, M. and Tsuge, T., 1995, 491– 498; Nishimura, S. and Kohmoto, K.,1983, 87–116). They can live in extreme conditions. They can easily let off spores which can be transferred in long distances by the air streams. The dark coloring of the spores protects them from the harmful influence of the ultraviolet rays. That is why they are spread all over the world. (Humpherson-Jones, F.M., 1985, 385-390; Kusaba, M. and Tsuge, T., 1995, 491– 498; Halfon-Meiri, A. and Rylski, I., 1983, 67-70)

One of the reasons for surviving of these fungi as plant pathogens is their ability to produce phytotoxins (Montemurro, N. and Visconti, A.,1992, 449–557; Johnson and al., 2000, 742–753). According to Ito and al.(2004, 399-411) the sort Alternaria alternata includes seven pathogenic sorts which produce different host-selective toxins and cause diseases on different plants including tobacco – tabacco pathotype (Slavov at al., 2004, 85-89).

It is possible for tobacco to be infected with the brown-spots-on-the-leaves disease at any stage of the vegetation – from the seedlings phase to physical maturity phase. The disease causes the biggest economic losses when the crop is infected before being gathered  in the drying houses. At that period the leaves which are being gathered in the drying houses are visibly healthy and the disease symptoms appear later in the course of drying.

Many sorts of Alternaria also produce non-host-specific toxins as bredelfin, altertoxin and tentoxin (Thomma, 2003, 225–236). They can influence a wide variety of hosts as they can provoke all or part of the symptoms which they provoke in the host plants (Vakalounakis,1990, 227-230; Thomma, 2003, 225–236). We must pay attention to these peculiarities when we introduce new crops in the tobacco sowing fields which become less every year. In the process of searching alternative crops many farmers turn their interests to the cultivation of healing plants because of the favorable soil and climatic conditions in the region which enable the growing of many non-traditional sorts such as stevia (Stevia rebaudiana Beroni).

The exotic herb comes from Paraguay and it is the best natural substitute for sugar. In its leaves it contains sweet substances – glucosides which are extremely suitable for people suffering from diabetes and also suitable for producing diet food and products. Because of its precious properties stevia use in the world production increases. In many states in the world the plant is included in scientific research programs for examination of its agrobiological properties.

The phytopathological estimation of the stevia plants grown in the experimental field of the Agricultural Institute of Shumen (Northeast Bulgaria) shows that yet in the first half of the vegetation period (from the planting till the end of July) 92% of the selected samples are infected with the brown-spots-on-the-leaves disease and in the second half of the vegetation we see increase of the disease intensity as the attack index can exceed 50% (Georgieva – Andreeva, 2013,100-104).

Materials and Approaches

The experiment was carried out in the laboratory of Plant Protection at the Agricultural Institute – Shumen. For the purpose of the research we have selected stevia leaves (from the experimental fields of the institute) and tobacco leaves (Burley) with brown-spots-on-the leaves disease, and the pathogens from the genus of Alternaria are isolated on an artificial feeding environment. From the isolates we have obtained monospore crops (by Drigalski’s method) which have been left for 14 days on potato-glucose agar in a thermostat. From the cultivated pathogens we have prepared spore suspensions with equal spore concentration (1500/1ml) with which we have infected tobacco leaves and put in a thermostat with high moisture. For controlling sample we have set samples processed with distilled water. The examination is executed with 10 repetitions (every leaf is one repetition) with the three variants – the controlling sample is with water and two samples of infection with suspension – with tobacco isolate and stevia isolate. On the third, seventh and tenth day we have accounted the diameter of the spots and the degree of infection (in grades by MacKinney).

The obtained results are processed statistically by the variation analysis method. (Zaprianov and Marinkov, 1978)

Results and Discussions

In figure 1 we can see the Burley tobacco leaf damage increase dynamics infected with fungi from the Alternaria genus from two different pathogen types during the 10 day examination period.

Figure 1. Development of the leaves-brown-spots disease

The results show that if there are suitable conditions, a host and a pathogen in a suitable phase of development , yet on the third day after the inoculation we can find the symptoms of infection. The difference between the average diameter of the lesions in the tobacco isolate variants and stevia variants is not significant. In comparison to the controlling sample (average diameter – 0.1 mm), in the inoculated with spores leaves, the spots are much bigger (in tobacco isolate – 12.9 mm, and in the stevia isolate – 10.4 mm) which shows that there is an accomplished contact between the host and the pathogens, i.e. there is a start of an infection process and and the inoculum obtained from stevia has pathogenic potential towards the tobacco leaves.

Table 1. Variation of the examined indicators – size of the spots and attack degree of the variants in the experiment

Control

3-rd day

7-th day

10-th day

Diameter

s

Cv

Diameter

s

Cv

Diameter

s

Cv

of the spots of the spots of the spots
average, mm average, mm average, mm

0,1 ( 0 – 1)

0,32

31,6

5,5 ( 0-15 )

6,29

11,4

11,6 ( 8-15 )

3,17

27,32

Degree of infection

0,1

0,25

0,5

average

Infected

Diameter

s

Cv

Diameter

s

Cv

Diameter

s

Cv

with

of the spots of the spots of the spots

suspension

average, mm average, mm average, mm

isolated from stevia

10,4 ( 8-15 )

2,67

25,72

31,5 ( 20-45 )

0,85

27,03

97 ( 55 -140 )

2,44

25,16

Degree of infection

0,75

1,4

4,2

average

Infected

Diameter

s

Cv

Diameter

s

Cv

Diameter

s

Cv

with

of the spots of the spots of the spots

suspension

average, mm average, mm average, mm

isolated from tobaco

12,9 ( 8- 25 )

4,98

38,58

36,5 ( 30-45 )

4,74

13

125 (95 -150 )

23,95

19,55

Degree of infection

0,95

1,7

4,7

average

The intensity of the infection growth till the seventh day since the set of the experiment is not high. We can see minimal differences in the diameter growth of the affected areas (table 1) which can be explained with the fact that for the germination of the spores (for the infection of the leaves) we need 24 hours in suitable conditions, and for the growth of the spots we need development and and spreading of the mycelium and also new spore formation. The size of the lesions of the controlling sample varies between 0 and 15 mm, and in the inoculated samples it is respectively between 20 and 45 mm (with stevia infection) and between 30 and 45 mm (with tobacco infection). Similar results have been reported regarding the indicator called attack rate. The colonized leaf area in the both samples treated with spore suspension is very small – average degree in the infected with stevia isolate – 1.4 and respectively – 1.7 in the samples infected with tobacco isolate.

Table 2. Statistical evaluation of the differences between the variants in the experiment on the tenth day since the inoculation

Diameter of the spots

Variants D SD t Provability
Control (with water)

85,4

2,36

36,18

***

With suspension from Alternaria isolated from stevia

 

Control (with water)

113,4

5,2

21,8

***

With suspension from Alternaria isolated from tobacco

 

With suspension from Alternaria isolated from tobacco

28

5,13

5,45

***

With suspension from Alternaria isolated from stevia

Attak rate

Variants D SD t Provability
Control (With water)

3,7

0,86

4,3

**

With suspension from Alternaria isolated from stevia

 

Control (with water)

4,2

0,59

7,11

***

With suspension from Alternaria isolated from tobacco

 

With suspension from Alternaria isolated from tobacco

0,5

1,04

0,48

n.s.

With suspension from Alternaria isolated from stevia

On the tenth day since the start of the experiment we can clearly see the differences in the size of the growth of the brown leaf spots on the treated leaves (122.5 mm in diameter in the tobacco isolate and respectively 97 mm – in the stevia isolate). The average diameter of the spots reported from the samples infected with Alternaria from tobacco is 20% bigger than the average diameter of the spots on the sick leaves infected from stevia spores which shows that there are differences in the inoculum quality of the both examined pathogenic types. This difference is statistically proven at the highest level (table 2).

We have very well secured difference of this indicator – spots diameter on the tenth day since the inoculation, and also there is secured difference between the treated variants and the controlling variant.

The intensity of the manifestation of the brown-spots-on-the-leaves disease is estimated via the indicator called attack rate. The average attack rate read in the controlling variant is very low – 0.5, and in the samples from the processed variants with stevia and tobacco isolates are respectively 4.2 and 4.7 which according to the working evaluation scale means that the bigger part of the leaf surface is colonized. The difference between the obtained results of the both variants is very small – 0.5. Between the compared materials there is no statistically significant difference.

Conclusions

Tobacco can be a host of the pathogenic sorts of Alternaria genus which cause brown leaf spots on the stevia.

The pathogens from the Alternaria genus isolated from stevia and tobacco differ regarding the type of infection reaction. In the variants contaminated with isolates from stevia the average diameter of the spots is 20% smaller than the average diameter of the spots on the leaves inoculated with tobacco isolates. Regarding the attack rate (% colonized area) there are no statistically significant difference.


References
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  2. Kusaba, M. and Tsuge, T. Phylogeny of Alternaria fungi known to produce host specific toxins on the basis of variation in internal transcribed spacers of ribosomal DNA. Current Genetics, vol. 28, no. 5, pp. 491–498. 1995.
  3. Nishimura, S., Kohmoto, K.Host-specific toxins and chemical structures from Alternaria species. Annual Review of Phytopathology. vol. 21, pp. 87–116. 1983.
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