In a previous study (Benslimane et al., 2011), eighty-two mono-conidial isolates of P. triticirepentis were recovered from Triticum aestivum and T. durum diseased leaves sample. The samples were collected from different geographical wheat growing regions of in Algeria (Table 1, Fig. 1). Briefly, leaf spotted area were cut into 3 cm pieces, surface sterilized in 5% hypochlorite solution for 3 min, then rinsed thrice in sterile water (5 min each time). The fragments were blotted on tissue paper to remove the excess water and placed in Petri dishes with three layers of dampened Whatman filter paper. The plates were incubated at 22°C for 24 h under light then in dark for 24 h. Single conidia from conidiophores (Fig. 2) developing close to the edge of each lesion were transferred to potato dextrose agar (PDA).

All 82 isolates were grown individually on PDA in plastic Petri dishes at 20°C in the dark. After one week, 5 mm diameter plugs were taken aseptically from the margins of actively growing cultures and placed fungus-side down in the center of fresh PDA dishes. Each isolate was replicated 4 times. Petri dishes were incubated in dark at 20°C, and then macroscopic characters (color, sector, and texture) of each colony were recorded after 7 days. PDA was choosing for this step and the next, because it is commonly used for the isolation and growth of wide range of fungi in laboratories.

All isolate hyphal growths were determined on PDA medium. To assess the effects of temperature on in vitro colony radial growth, small plugs, 5 mm in diameter were transferred singly to 9 cm Petri dishes containing PDA. Cultures were incubated in the dark at three temperatures (20°C, 25°C, and 30°C), mycelium radial growth was recorded for each isolate in mm at 24 h interval until the colonies had reached the plate edge. Four diameters of linear growth of each plate were measured at right angles to each other and the values were averaged. Four replications (one plate/rep) were used for each isolate and for each temperature. Means values were used to perform principal component analysis using STATISTICA software (StatSoft Inc., Tulsa, OK, USA).

To determine whether any differences in conidial width and length exist within or among the isolates, 42 isolates were selected randomly and spores were produced of each isolate following the protocols of Lamari and Bernier (1989). Small plugs, 0.5 cm in diameter, from 8 day culture were transferred singly to 9 cm Petri plates, containing V8-PDA. The cultures were incubated in the dark until the colonies reached 4 cm in diameter. The cultures were then flooded with sterile distilled water and the mycelium flattened with the bottom of flamed test tube. After the water was decanted, the cultures were subjected to a regime of 18 h of light at room temperature followed by 24 h of dark at 15°C. Conidia size (length, width) and septation number of 50 spores/each isolate were counted under 40× magnifications with the aid of ocular and stage micrometer in compound microscope. Spore measurements were compared among the isolates and data were analyzed statistically by ANOVA method using SPSS software (SPSS Inc., Chicago, IL, USA).

The P. tritici-repentis isolates used in this study varied in colony color and mycelium compactness. Cultures growth on PDA medium showed usually a thick cottony mycelium sometimes fluffy, often gray-green (Fig. 3), and rarely whitish (Fig. 4). Underside the colony color was green (Fig. 5). The old cultures about two weeks showed black spherical mycelia aggregations (Fig. 6). Moreover we found that when the mycelium color became orange, the isolates loosed the ability to produce spores as a result of a repeated sub-culture in PDA medium (Fig. 7).

The results on radial growth of all isolates colonies at different temperatures showed that the mycelium growth is temperature depended (Table 2). It was observed that the temperature range of 25-30°C was optimum for mycelial growth of P. tritici-repentis on PDA. Indeed, most of the isolates (57) showed a better (3.72-6.95 mm) growth at 25°C; however, some (10) of the isolates grew better at 30°C. Only five isolates (Ptr16, Ptr20, Ptr41, Ptr48, and Ptr72) grew (3.45-5.55 mm) better at 20°C. Based on radial growth at the three different temperatures, the principal component analysis categorized the isolates into six groups (Fig. 8); some of these groups stand out more than others; such as the group consisting of a single isolate Ptr6, or the group combining Ptr52 and Ptr64 (Table 1).

Even the different analyses of the results of mycelia growth showed that there was some difference between the studied isolates, the effect of temperatures, expressed trough the radial growth, showed that the difference or the approximation among studied isolates, seems to have no relationship with the geographical origin of the isolates. It was found that pathogen population in closely located fields or in the same, consisted of specimens of large phenotypical variability. Otherwise, it does not show any relationship with the climate of the area from where the sample was collected. In deed in Fig. 8, we can see isolates from different geographical regions grouped together, as well as other isolates from nearby areas classified statistically in groups far away each other.

P. tritici-repentis isolates produced abundant conidia on V8-PDA which were consistent in morphology. Significant differences were founded in conidial length and number of cells among the isolates (P = 0.000). Dimensions of the conidia for each isolate are presented in Fig. 9 and Fig. 10. Average conidial length was maximum (217.67 μm) in isolate Ptr10 and minimum (117.15 μm) in Ptr71 whereas the number of septa varied from 11.52 in isolates Ptr11 to 5.42 in isolate Ptr21. However, no significant variation was observed in conidial width; only two values were founded 15.6 μm and 18.2 μm.