In Punjab, guava is grown in all districts because climatic conditions and soil is suitable for its cultivation. Pear shaped guava is produced in Larkana district, Sindh. In NWFP, the production of guava is 18570 tones and cultivated on an area of 1557 ha (Agricultural Statistics of Pakistan 2004 -2005).
Guava fruits twice in a year that’s why it is available in market throughout the year. Commercially grown varieties in Pakistan are white Allahabadi, red Allahabadi, shaikhupori and local/Desi amrood. Potential constraints for production of guava includes less post-harvest techniques. It is normally considered that about 20% of production of guava is wasted or thrown away. Instead of gaining, the production is lost (Malik, 1993).
The most common definition of endophytic fungi is that of Petrini (1991), “All organisms inhibiting plant organs that at some time in their life, can colonize internal plant tissues without causing apparent harm to the host”. Endophytic fungi are group of fungi that causes Infections like asymptomatic infections on aerial tissues of different group of plants. The majority of fungal endophytes are ascomycetes and their anamorphs. Basidiomycetes and zygomycetes rarely are isolated as endophytes (Petrini 1986).
Group of these fungi do not affect the plants communities too much. They are not harmful to plants. They provide resistance to plant against insects (Azevedo et al.2000), fungal pathogens (Arnold et al. 2003, Dingle & McGee 2003). Endophytic fungi increase the plant ability to stand and continue its life cycle in harsh environments (Redman et al. 2002).
There have been a lot of work is done on endophytic fungi and their relation with plants (Bills 1996), and many tropical plants have been observed for their relation with fungal endophytes association (Arnold, Maynard & Gilbert 2001, Cannon & Simmons 2002, Suryanarayanan, Murali & Venkatesan 2002, Suryanarayanan, Venkatesan & Murali 2003). Fungal endophytes causes many damages to their host such as stress enhancement, disease and insect resistance (Elzik 1985; Bush et al. 1997; Clay & Holah 1999; Shimizu 2000), improvement of productivity (Quaroni et al. 1997; Shimizu et al. 2001), and activities of many herbicides by making an association with their host (Peters et al. 1998).
The colonization of endophytes and propagation and secondary metabolites which are present inside the plants may be important for above effects. These opinions’ shows that endophytic fungi may be used as biological agents for the control of insects and many diseases (Miller 1995).
Nickel is one of the important micronutrient required by plants. It is required by plants in very minute quantity for optimum growth of a plant (Brown et al., 1987; Eskew et al., 1983, 1984). Higher concentrations of nickel applied to plants may cause serious damage to plants. If it is applied near to stem or, when applied to plants, it touches the stem of the plants or leaves may cause yellowing of leaves or branches (Bingham et al, 1986; Farago and Cole, 1986; Foy et al., 1978). High concentration of nickel many important physiological and biological process like making leaf chlorophyll content of plants and necrosis of leaves (Pandolfini et al., 1992; Piccini and Malavolta, 1992).
Nickel also effect the chemicals that aids in photosynthesis and also effect the transpiration rate of a plant (Carlson, 1975; Jones and Hutchinson, 1988a; Morgutti et al., 1984; Rauser and Dunbroff, 1981). The symptoms of nickel toxicity include chlorosis of leaves which is followed by mottling. Plant leaves also show sign of necrosis and stunted growth of plant stem and other parts (Hutchinson, 1981; Khalid and Tinsley, 1980; Misha and Kar, 1974; Yang et al., 1996).These symptoms in plants often noticed when there is imbalance of mineral nutrients or disturbance in nutritional status of soils.
Ni symptoms in plants are often considered to be Cu symptoms when plants are grown in contaminated soils or in soils that have high concentration level of Ni (Craig, 1978; Dang et al., 1990; Farago and Cole, 1986). Ni toxicity effects the uptake of other nutrients like Zn, Fe, Cu and Co in tomatoes (Lycopersicon esculentum L.).
Safeer Asad, Muhammad Wajid Khan, Muhammad Zubair, Rashad Mukhtar Balal and Muhammad Adnan Shahid,
Department of Horticulture, University College of Agriculture, University of Sargodha