Abstract: Eight strain/isolates of seed-borne Fusarium solani tested for pathogenicity on sunflower, sesame, tomato, wheat and millet showed variations in pathogenicity in in vitro on test host. Some strains were found pahtogen in their original host while some isolates showed pathogenicity on other host with out causing rot on roots of their original host. Culture filtrates of these eight strains of F. solani also showed variation in antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Fusarium solani (roots isolates).
Introduction
The genus Fusarium occurs widely in nature as saprophytes in soil and decaying vegetables, some species are plant parasites, where specialized pathotypes may cause vascular wilt, stem rot, fruit rot, ear diseases and damping off (Booth, 1971; Domsch et al., 1980). The genus has also acquired notoriety because of the ability of serval species to produce toxic metabolites causing illness and even death in man and domesticated animals (Moss and Smith, 1984). Of the various species of Fusarium, F. Solani is one of the most ubiquitous soil fungus and a destructive plant pahtogen of hundreds of hosts, causing chiefly root and fruit rots (Booth, 1971; Domsch et al., 1980), readily isolated pathogenic fungus from seeds and considered as more serious threat to crops, due to its close proximity to growing roots (Neergaard, 1977).
Apart form destructive role, a number of naphthaquinone type pigments including fusarubin, anhydro-fusarubin, javanicin, methy1 ether-fusarubin, marticin, isomarticin, lactone are ethy1 ether-fusarubin, solaniol, nectriafusarubin and dihydro-fusarubin lactone are known to produce by F. solani (Kurobane et al., 1980; Baker et al., 1981; James and Robert, 1983; Tatum et al., 1985). Some naphthaquinones have antimicrobial (Mokhtar et al., 1979) and nematicidal properties (Hameed et al., 2001). Fusarubin, a pigment isolated from F. solani showed antimicrobial, phytotoxic and antitumor properties (Arnstein et al., 1946; Issaq, 1977). Although enormous literatures are available on the pathogenicity of seed-borne F. solani but no data is available on the antimicrobial activity of the same strains. This report describes the pahtogenicity of seed borne F. solani on their original and other hosts. Animicrobial activity of culture of F. solani strains was also examined.
Materials and Methods
Eight strains of Fusarium solani used in this study were isolated from seeds of different hosts viz., S-29 (Sorghum bicolor), B-17 (Brassica compestris), C-10 (Capsiucm annuum), SS (Helianthus annuus), TS (Lycopersicon esculentum) and L-25 (Lens culinaris).
Pathogenicity of F. solani: Seeds of test plants viz., (Helinathus annuum), sesame (Sesamum indicum), tomato (Lycopersicon esculentum), Wheat (Triticum aestivum) and millet (Pennisetum americanum) were surface sterilized with Ca(OH)2 and transferred on sterilized petri dishes having blotters paper. After coming out of the radical, seeds were transferred onto periphery petri dishes containing potato dextrose agar, in a position to ensure that The germinating radical face towards the center of the petri dishes. Test cultures of the F. solani placed in the center of petri dishes and incubated at 28°C for 3-5 days. The browning of the roots were recorded when test fungus touches the roots.
Antimicrobial activity of culture filtrates of F. solani: Fungi were grown on Czapeks Dox broth for 15 days at 28°Cl. After 15 days each strain was filtered over paper Whattman No 1. The culture filtrates obtained were used as such (1:0) or diluted as 1: 10 and 1:100. Sterlizied thick filter paper discs were impreganated with each dilution (20 μl disc–1) and dried.
Antibacterial activity: Petri dishes containing Tripticase soya agar were seeded with test bacteria like Staphylococcus aureus Rosenbach, Bacillus subtilis Chon and Escherichia coli (Migula) Castellani and Chalmers with the help of a sterilized cotton swab. Discs of the culture filtrates and control were placed at different positions in the petri dishes. Discs impregnated with Czapex Dox broth served as control, while streptomycin served as+ve control @ 10 μg disc–1. Each treatment was replicated 3 times and plates were incubated at 30°C. Observations were recorded daily. The zone appeared around the discs was considered as zones o inhibition.
Antifungal activity: In order to determine the antifungal activity of culture filtrates of F. solani, loaded discs with culture filtrates were placed at different places of petri dishes containing Czepak’s’s Dox agar (pH 7.2) with one control and one standard fungicide (Benlate) @ 10 μg disc–1, served as positive control. A 5 mm disc of actively growing culture of F. solani (roots isolates), were inoculated in the center of the dish and incubated at 28°C. Each treatment was replicated 3 times and observations were recorded daily. Zone of inhibition produced were measured in mm and averaged.
Results
In pathogenicity test, F. solani strain T-9 isolated form tomato seed was found pathogenic on sunflower and millet, not on tomato.
| Table 1: | Pathogenicity of Fusarium solani strains on seedlings of different plants |
| + Root tips brown, ++ About half root brown +++ Whole root brown | |
| Table 2A: | Growth inhinitions of Staphylococcous aureus by culture filtrates of deed-brone F. solani strains |
| Table 2B: | Growth inhibitions Esherichia coli by culture filtrates fo seed-borne F. solani stranis |
| Table 2C: | Growth inhibitions of Bacillus subtilis by culture filtrates of seed-brone F. solani strains |
| Table 3A: | Antifungal activity of cultural filtrates of seed-brone F. solani strains against sunflower roots infecting F. solani isolate |
| Table 3B: | Antifungal activity of culture of seed-borne F. solani strains against chilli’s roots infecting F. solani isolate |
from tomato seed was found more pathogenic on millet and less on tomato seedling. F. solani strain S-29 (sorghum isolate) was pathogenic on sunflower, millet and tomato. Strain SS isolated from sunflower was more pathogenic on sunflower than millet (Table 1).
| Table 3C: | Antifungal activity of culture of seed-borne F. solani strains against wheat’s roots infecting F. solani isolate |
While other strain TS also isolated Maximum growth inhibition of Staphylococcus aureus was found by strain TS followed by S-29. Maximum zone was produced by strain TS (15 mm) followed by SS (12 mm). All the test F. solani strains inhibited B. subtilis, with maximum zone was produced by S-29 (14 mm) followed by C-10 and T-9 (10 mm). Antibacterial activity of F. solani strains was reduced when diluted (Table 2A-2C). Here inhibition potential of cultural filtrates of seed borne F. solani were tested against radial growth of F. solani isolated from sunflower root, culture filtrates of T-9, S-29 and L-25 inhibited the radial growth of F. solani. Whereas wheat’s root and chilli’s root isolates were inhibited by culture filtrates of T-9 and L-25 strains of F. solani. Diluting of culture filtrates either reduced or loss the antifungal activity (Table 3A-3C).
Discussion
Fusarium solani causes a variety of diseases in plants in plants such as wilt, blight root and stem rot (Janke, 1976) and was found associated with root rot of greenhouse tomato (Armstrong and Armstrong, 1978) and soybean seedlings (Grant, 1980). In Pakistan F. solani has been reported to cause root rot disease in a number of economic crops (Ehteshamul-Haque, 1994). In this study seed-brone F. solani strains showed tremendous variations in pathogenicity on various hosts. It is interesting to note that some strains were found non-or less pathogenic on their original host while found pathogenic on other host.
In this study, culture filtrates of F. solani strains showed antibacterial activity against B. subtilus, E. Coli and S. Aureus and antifungal activity against some roots isolates of F. solani. Many antibiotics and mycotoxins were produced by strains of Fusarium species (Burmesiter et al., 1974). There are reports on naphthazarin pigments fusarubin, anhydrofusarubin and javanicin isolated from culture filtrates of F. solani which were found to possess insecticidal activity on blowfly Calliphora erythrocephala (Claydon et al., 1977). Fusarubin has also been reported to have antimicrobial (Arnstein et al., 1946) activities. In this study F. solani strains showed tremendous variations in antimicrobial activity. Variation in their antimicrobial activity is presumably due to genetic makeup (Domsch et al., 1980), a marked variations in F. solani isolates have been reported (Burnett, 1984). Strains of F. solani could be exploited for the isolation antimicrobial compounds.