RESULTS AND DISCUSSION

Table of Contents:

Fungi responsible for causing diseases are a major factor in the low productivity of a crop. In this respect, cereals grains such as barley can easily be colonized by fungal species, which cause their deterioration (Soldevilla et al., 2005). All barley samples in the upper valleys of the states of Guanajuato, Hidalgo, and Puebla that were sampled showed fungal strains. From a total of 13 lots of samples of barley seeds with disease symptoms, 64 strains of phytopathogenic fungi were isolated, of which 27 were recovered from the variety Esmeralda, 13 from the Adabella variety, 11 from the variety Josefa, 9 of the Forrajera variety, and 6 of the Gaviota variety of barley (Table 15.2).

The results obtained in this research are similar to those reported by other authors for other barley-producing areas of the world (Soldevilla et al., 2005; Ocampo et al., 2005; Lowe and Ulmer, 2006; Bolton et al., 2008; Garcia et al., 2012).

In other studies, the presence of Penicillium and Aspergillus genera as predominant fungi has been reported in barley grains (Scudamore and Hetmanski, 1995; Maenetje and Dutton, 2007). However, our results do not coincide with those reported by these authors because in this study the species isolated from the genus Penicillium (Table 15.2) are not predominant fungal genera. This result may be due to the presence of other genera of fungi of greater economic importance for this crop (Fig. 15.2).

Within these important genera that were isolated as predominant is the complex of rust of cereals. Species of this genus have been reported to be responsible for causing diseases such as P striiffformis “4.5%” (Wellings,

2010), and brown rust caused by P triticina “4.5%,” P hordei “7.5%,” and P recondite “3.0%” (Steffenson et al., 1993; de Vallavieille-Pope et al., 1995; De Wolf et al., 2010; Bolton et al., 2008; Sanchez, 2011). The other predominant fungal genera in this study were Fusarium and Rliizopus with 18.5 and 15%, respectively. The genus Fusarium is responsible for causing fusariosis of the spike, a disease whose importance lies in its low yield and the toxins generated in the affected grains (Gilchrist-Saavedra et al., 2005).

All geographic areas where cereal crops are grown in Mexico present problems against Fusarium spp., vaiying the species at each location and at different times (Ireta and Gilchrist, 1994; CIMMYT, 2004). The losses can vary considerably, many times not being related to the yield, but yes with the content of toxins present in the grains. That is why big companies that use grain to make concentrated animal feed or cereals in flakes, for human consumption, control the content of toxins, imposing limits on their concentration. However, when there is no way to control the toxin content, infected grains become a health problem (Gilchrist-Saavedra, 2000).

In relation to R. oryzae, this genus has been reported to cause diseases of fruits of several species, such as strawberry (Fan-era et al., 2007), tulipan (Hisaki et al., 2006), cocoa (Cuervo-Parra et al., 2011), and barley

Fungal species

Variety of barley

Adabella

(JCPn)

Esmeralda

(JCPn)

Gaviota

(JCPn)

Forrajera

(JCPn)

Jose fa (JCPn)

% of total occurrence in isolationa

Drechslera teres

7,50

2, 10, 19, 51

-

-

16, 57

32.00

Bipolaris somkiniana

6

3, 12, 30

-

43, 65

14. 44

32.00

Fus ahum gram inearum

28, 53

1, 34, 55, 62

59

-

15, 64

36.00

Fusahum austroamehcanum

-

-

-

40

-

4.00

Rhizopus oryzae

9,27

0, 20, 29

22

24, 41

18, 45

40.00

Fusahum pseudograminearum

-

-

46

-

47

8.00

Puccinia tiiticina

8

-

21

-

17

12.00

Puccinia striifonms

26

35

-

-

58

12.00

Puccinia recondita

37

-

-

38

-

8.00

Puccinia hordei

54

48, 61

60

39

-

20.00

Alteniaha allernala

-

13, 31,32,49,56

-

25

-

24.00

Penicillium oxalicum

63, 52

11,4

-

42

-

20.00

Pen iciUium citrinum

-

5,33

-

-

-

8.00

Penicillium digitatum

-

36

23

-

-

8.00

“Percentage of occurrence for и = de 25 Petri dishes with PDA medium (5 replicates per barley variety). n: identification number of each strain.

(Romero-Cortes et al., 2016). Although this species is not reported as a pathogen of barley, their rapid growth observed during its isolation would allow it to colonize and destroy the seeds and plants in a very short time, being the first report of this fungus as pathogen for this crop in Mexico.

Percentage of more predominant genera

FIGURE 15.2 Percentage of more predominant genera.

The measurements of different morphological structures of phytopatho- genic fungi are described below. For Rhizopus oryzae the colonies showed a diameter of 75-80 mm, sporangiophore with stipes of more than 1500 pm in length, sporangium of more than 150 pm in diameter and conidia of 5-8 pm in length. For Drechslera teres colonies shown 5.1 mm/day growth rate, conidiophores showed different shape (64-79 x Ю-17 pm), and conidia being in the range 36-102 x 13-15 pm. In the case of Bipolaris sorokiniana, colonies grew on PDA medium showed a diameter of 35-40 mm, abundant sporulation of conidiophores with size of 130-154 x 6-8 pm, conidias are dark olivaceous brown with a size of 77-146 x 15—19 pm. In the case of Alternaria alternata, colonies in PDA medium showed a rapid growth with a diameter of 37-40 nun in 7 days. Conidias were small to moderate in size, 20-29 x 8-10 pm.

For Fusarium graminearum, F. austroamericanum, and F. pseudoameri- canum, it was observed that their growth was 5, 5.6, and 5.3 pm/day, respectively. In all three species, the presence of macroconidia was observed, ranging from 2.5 x 35-65 pm, with globular chlamydospores of 10-12 pm in diameter. The presence of microconidia was not observed. On the other hand, in the case of the barley rust, it was observed that Puccinia recondita

showed uredospores of brown color and spherical shape of 16-28 pm in diameter. Fori3 striiformis the uredospores were spherical to ovate in shape, orange colored, and with a size of 23-35 x 20-35 pm. Puccinia triticina showed uredospores of brown color and of oval form of around 25-30 x 15-20 pm. Finally, P hordei showed spherical uredospores in shape, orange, and with a size of 13-18 x 10-14 pm. For fungi of the genus Penicillium (P oxalicum, P. citrinum, P digitatum), blue-green conidia with a growth diameter of 35-40 pm were observed at 7 days of growth. The conidia were round to ellipsoidal in P oxalicum, unicellular and observed as chains not branched at the end of the phialide, between 2 and 5 pm in diameter. The morphological characteristics of the fungal species isolated from barley grains are shown in Figures 15.3 and 15.4.

Macroscopic characteristics of fungal species isolated from barley plant seeds

FIGURE 15.3 Macroscopic characteristics of fungal species isolated from barley plant seeds.

Microscopic characteristics of fungal species isolated from barley plant seeds

FIGURE 15.4 Microscopic characteristics of fungal species isolated from barley plant seeds.

CONCLUSIONS

Knowledge of the fungi species present in a particular crop is of utmost importance to be able to implement strategies aimed at the prevention and control of the diseases that these fungal agents can cause in the cultivation of barley. Likewise, the use of reliable techniques for the identification of strains of phytopathogenic fungi is of equal importance to avoid their dispersion within an area.

KEYWORDS

  • hordeum vulgare
  • phytopathogenic fungi
  • morphological characterization
  • barley
  • microorganism

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