Most known fungal species are strictly saprophytic, with less than 10% of the more or less 100.000known fungal species able to colonize plants Carlile et al. (2001). Plant parasitic fungi have dominated the living plants as an abundant source of nutrients ( Mendgen et al., 1996). But there is a different level of specialization in plant-fungal interaction. The first group include involves true pathogens that rely on living plants but can grow outside of their hosts. The second group the opportunistic parasites which enter plants through wounds or new hair roots. These species are usually low virulence (Jackson and Taylor 1996).
Fusarium oxysporum causes wilt diseases in a wide variety of economically important plants and cause a destructive loss in the crops production (Gordon 1997). Managing Fusarium wilt disease is a achieved through chemical soil fumigation and resistant cultivars. Now there are available broad spectrums of biocides used to fumigate soil before planting as Captan, Benomiel and other commercial varieties ( Fravel et al., 2003) But they are have a negative impact on the environment . The environmentally save method is the use of BCAs.
But[W2] resistance breeding are very difficult when no dominant gene is known (Fravel et al., 2003). Further more the pathogen can overcome the plant resistance. Virulent races of F.oxysporum f.sp. ciceris have undermined the importance of resistant cultivars of chickenpea ( Haware and Nene 1982). Fusarium sporum pathogensis Pathogensis describes the complete process of disease development in the host, from initial infection to production of symptoms (Lucas 1998). During the initial stage of the interaction, fungal pathogens must sense stimuli from the plant and respond with appropriate morphogenic and biochemical changes (Gordon 1997).
Effects caused by pathogens on plants are almost entirely the result of biochemical reaction taking place between substances secreted by the pathogen and those present in or produced by the plant. During pathogensis the fungus penetrate in defence barriers that plant cell walls comprise of ( Mengden et al., 1996).The pathogenic fungi secrete a mixture of hydrolytic enzymes including cutinase, cellulase, pectinase and proteases ( Knogge 1996).After penetration the fungus produce toxins that manipulate plant physiology ( Walton 1994).
Factors Enhance F.oxysporum pathogenesis Temperature F.oxysporum optimal growth was found to be between 25 and 28O C Carlile et al. (2001).The growth of the Fusarium wilt pathogeneses disease was maximized at 28 C and inhibited above 33 C, and not favoured below 17 C. Jackson et al. (1990) recorded the relationship between substrate temperature and disease intensity, when they found wilt symptoms in carnations did not developed at extreme high or low temperature a little colonisation was found at 14 C. More severe sympotoms of wilt chickpea were found at 25 and 30 C than at 10, 15, and 20 ( Bhatti and Kraft 1992). Fusarium wilt of carnation was developed at 85% shade Carlile et al. (2001).
Harling et al., 1988 suggested that temperature alter the balance between the host plant and Fusarium wilt pathogen.The effect of temperature on wilt occurrence may vary in different pathosystems( Ben-Yephet and Shtienberg 1997). Brake et al., 1995 found that the impact of temperature was on plant growth not on the pathogen. F.oxysporum f. sp. cubense is present in some tropical regions, it severly affects banana in the subtrobics, indicating that temperature may have an important influence on disease development ( Ploetz et al., 1990).
Ph Increasing soil pH has appositive effect on Fusarium wilt disease reduction (Jons and Woltz 1973). The explanation for this effect are, The domination of advantageous and disease -suppressive in the root rhizosphere at high pH. And the effect of pH on micronutient availability in the media and its impact on the growth , sporulation and virulence Jones et al., 1989. F.oxysporum mycelia grow within range of pH 2-12, how ever F.avenaceum started to grow at pH 3.
But all species were observed to grow at pH 6, Srober 1978).Wilson,1946,found that acid soil (pH4.2) supported Fusarium growth, whereas a pH near neutrality prevented this growth .Raising soil pH toward neutrality appears to be a foundation in controlling Fusarium wilt, which is a commonly disease associated with acidic conditions ( Woltz and Jones 1981). F.oxysporum spores germination were influenced by the difference in the pH (Peng et al. 1999)
Nutrition The stages of Fusarium growth depend on the ecological balance and nutrient availability ( Woltz and Jones 1981).Fusarium oxysporum is an autotroph, requiring only a carbon source for structure and energy, and inorganic compounds to synthesized organic compounds such as sugars, lipids and amino acids ( Woltz and Jones 1981). Increasing nitrogen levels in the soil generally lead to an increase in Fusarium wilt development (Woltz and Jones 1973) Ammonium form of nitrogen becomes more favourable for Fusarium disease with increasing the rate of application( Woltz and Jones 1973), and reported also F.oxysporum cultured on ammonium nitrogen was more virulent than the cultured on nitrate nitrogen form.This work was aiming to understand the physiology patterns of F.oxysporum f. sp. gladioli strainsthat regulate the fungus virulence.
The aim of this was is to investigate and gain more understanding for physiological factors affecting F.oxysporum f. sp. gladioli growth. Materials and methods Fungal isolates F.oxysporum f.sp. gladioli strains ( 640, 160) were purchased from the Centraalbureau voor Schimmelculturen, The Netherlands, but Go10 strain s was obtained from a Gladiolus Big Flower GT01 corm. Cultures were maintained on PDA (Oxoid, Basingtoke, Hants, UK) at 22?C and routinely sub-cultured at 15 day intervals, to be used as a fresh stock cultures for sub-culturing. 640 and 160 strains were delivered as freeze dried spores.
Spores were suspended in 1 ml sterilitiezed water and cultured on PDA plates for 15 days. Cultures were maintained on PDA (Oxoid, Basingtoke, Hants, UK) at 22?C and routinely sub-cultured at 15 day intervals, to be used as a fresh stock cultures for sub-culturing. Subcultures were prepared by inoc6lating PDA with 1 cm diam. disks of colonized PDA plus mycelium, cut from the edge of an actively growing, 7 day old colony. The new plates were incubated at 25O C for 7 days. The 10-mm disk diameter was subtracted from this value. Five plates were incubated for each treatment and the experiment was repeated.