BIOTIC EFFECT OF PHYLLOSPHERIC FUNGI ON THE GROWTH AND DEVELOPMENT OF SEIMATOSPORIUM HYPERICINUM (CES.) SUTTON

Beata Zimowska

ABSTRACT

The study examined the effect of 17 fungi species obtained from the leaves and stems of St. John’s wort (Hypericum performatum L.) on the growth of Seimatosporium hypericinum. The fungi that strongest limited the growth and sporulation of S.hypericinum included Trichoderma spp. and Gliocladium roseum. The studied species from the genus of Trichoderma caused complete death colonies and conidiospores of the pathogen as early as after 5-12 days, while G.roseum after 34 days of common growth. The growth of S.hypericinum was also inhibited by the fast growing species from the genera of Fusarium and Botrytis cinerea, Rhizoctonia solani and Phoma exigua var. exigua. With its common growth with C.gloesporioides and P.janthinellum, the pathogen formed an inhibition zone of 1-2 mm.

Key words: antagonistic fungi, Seimatosporium hypericinum..

INTRODUCTION

Seimatosporium hypericinum (Ces.) Sutton causes red spots on the leaves and the necrosis of the stems of St. John’s wort (Hypericum perforatum L.). Infecting the aboveground parts of plants, the fungus contributed to the decrease of the quantity and the quality of the raw material of Herba hyperici [16, 17]. A specific application of St. John’s wort as a medicinal plant as well as the recommendations concerning the introduction of the Good Plant Protection Practice in herbal production justify the purposefulness of using biological methods for the protection of the plantation of Hypericum perforatum L. from S. hypericinum [1, 13]. In India, antagonistic strains of Trichoderma harzianum and T.aureoviride are used in limiting the wilt of caraway (Carum carvi L.) caused by Fusarium oxysporum f. sp. cumini [14], while the strains of T. harzianum were used in the case of F.o.f. sp.zingiberi infectin g ginger (Zingiber officinalis Rosc.) [11].

Because of considerable harmfulness of S. hypericinum towards the leaves and stems of St. John’s wort [15, 16], which was shown in the years 1998-2000, studies were undertaken on the antagonistic species of fungi towards this pathogen.

MATERIALS AND METHODS

The study material consisted of isolate D 1080 Seimatosporium hypericinum and 17 other accompanying species isolated in 1998-2000 from the leaves and stems of St. John’s wort with necrotic symptoms. They included Colletotrichum gloeosporioides obtained in the last year of studies [17]. The studies on the biotic effect of fungi were conducted by the method of biotic series according to K. Mańka on PDA medium [9]. Evaluation of biotic relations was performed according to an eight-grade scale [9]

In the case of Trichoderma spp. and Gliocladium roseum, studies were also carried out on their influence on the viability of S. hypericinum if the surface of the pathogen colony was covered by the mycoparasite [7].

RESULTS

The studies showed that among the 17 analyzed species, 14 limited the pathogen growth, which is shown by positive values of individual biotic effects (Tab. 1). The maximum values of +8 occurred in the case of Botrytis cinerea, Rhizoctonia solani and Trichoderma spp. (Tab. 1). The colonies of Trichoderma harzianum and T. aureoviride grew over ¼ of the surface of the pathogen colony after two days, while after four days they grew over the whole surface. T. polysporum covered the colony of S. hypericinum after 10 days of common growth (Fig. 1). In the case of T. koningii, the colonies were contiguous already after the first day of growth, while after three they completely covered the colony of S. hypericinum (Fig. 1). Degeneration of the hyphas and conidiospores (Phot. 1), and then the death of the whole pathogen colony, to ok place after five – twelve days, depending on the fungus species (Fig. 1).

In contrast to Trichoderma spp., the colonies of Gliocladium roseum approached the colonies of S. hypericinum as late as after 16 days of common growth, while after nineteen days they colonized ¼ of the pathogen colony (Fig. 1). After thirty days the whole colony of S. hypericinum was covered with the mycelium of G. roseum, while the hyphas of the mycoparasite wound around the hyphas of the pathogen, grew inside them and inside the conidia, in this way causing a lack of their viability (Fig. 1, Phot. 2).

The fungi species from the genera of Fusarium and Phoma exigua var. exigua also inhibited the growth of S. hypericinum, which is shown by the positive values of the individual biotic effect ranging from +6 to +5 (Tab. 1). Alternaria alternata turned out to inhibit the pathogen growth only in a slight degree since the value of the individual biotic effect for this species was +3 (Tab. 1). On the other hand, Cladosporium cladosporioides showed a neutral effect towards S. hypericinum, which is proved by the value of the individual biotic effect of 0 (Tab. 1). A negative biotic effect showing a lack of the inhibiting effect towards S. hypericinum was found for Penicillium janthinellum and Colletotrichum gloeosporoides since the value of the individual biotic effect for those species was -2 and -1, respectively (Tab. 1). Besides, S. hypericinum, with its common growth only with the two enumerated fungi species, formed an inhibition zone ranging from 1 to 2 mm.

DISCUSSION

The fungi tested and considered in the studies, independently of the frequency of their occurrence, made it possible to find out the way in which a number of species affect S. hypericinum. A strong inhibiting effect of fungi from the genus Trichoderma should be considered as positive in the aspect of their practical utilization as elements supporting the biological control of this pathogen. Trichoderma spp. are known for their competitive capabilities, the abilities to form exo- and endo-enzymes, toxic metabolites as well as the ability of overparasitism [3, 6, 10]. Probably thanks to those mechanisms of direct effect on the pathogen, the studied Trichoderma spp. caused growth inhibition of S. hypericinum and degradation of the mycelium hyphas and conidia of the pathogen [10]. Among the examined species from the genus Trichoderma, the species T. koningii turned out to be the strongest antagonist towards S. hypericinum. Considerable fre quency of the occurrence of this fungus, especially in 1999, suggests that it had a significant effect on high positive values of the general biotic effect. The results point out that the inhibiting effect of S. hypericinum was also affected by the fast growing species that were at the same time pathogens of herbal plants [2, 5, 8]. Therefore, the possibility should be taken into consideration that the colonies of S. hypericinum will be grown over by the enumerated species while isolating the fungi from the plant tissues, especially when the medium used for isolation is not adequate for the growth of S. hypericinum [15]. A slight positive biotic effect of Gliocladium roseum towards S. hypericinum observed only after 10 days probably results from small competitive abilities of this mycoparasite [6]. Over-parasitic abilities of G. roseum towards S. hypericinum, which are shown only after 34 days of common growth point out that the estimation of full effect of G. roseum as an over-parasite is methodologically correct only after this time.

On the other hand, in the case of two dangerous pathogens of the aboveground parts of St. John’s wort, i.e. S. hypericinum and Colletotrichum gloeosporioides [4, 12], a slight superiority can be reached by the former due to its ability to secrete metabolic products of antibiotic properties. This is shown by the inhibition zone formed by S. hypericinum during its common growth with C. gloeosporioides. Hence, the co-existence of these two pathogens is rather difficult and the superiority will be reached by the species that will find favourable conditions for its growth.

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