Slow rusting resistance in 19 promising wheat lines to yellow rust in Ardabil, Iran.

Yellow rust caused by Puccinia striiformis f. sp. tritici is undoubtedly, the most important fungal disease of wheat especially in central and Western Asia that causes significant annual yield losses. Production and use of cultivars with durable resistance is the best controlling method. For this purpose, study on reaction of 19 promising lines to yellow rust was carried out in Ardabil in 2008-2009 cropping year. Assessment of adult plant reaction was conducted under field condition with artificial inoculation. Seedling test was also conducted in greenhouse. Slow rusting resistance at adult plant stage was assessed through the Infection Type (IT), Disease Severity (DS), Relative Area Under Disease Progress Curve (rAUDPC) and Coefficient of Infection (CI). Results of mean comparison of CI and rAUDPC indicated that the lines; C-87-1, C-87-2, C-87-3 and C-87-18 had the highest CI and rAUDPC. The lines C-87-6, C-87-8 and C-87-11 had the susceptible reaction at seedling test and were moderately resistant to moderately susceptible at adult plant stage. Consequently, these lines with low rAUDPC (15.2 to 27.8%) most probably could have slow rusting resistance. The lines C-87-4, C-87-5, C-87-13, C-87-14 and C-87-17 had not any infection or were at low level of infection, thus, they were selected as immune or resistant lines. The rest lines were moderately resistant to moderately susceptible. In this study, correlation analysis of different parameters also showed highly strong relationship of CI with rAUDPC and disease severity (R2 = 0.91 and 0.98, respectively).

Effect of nutrition on growth and virulence of the entomopathogenic fungus Beauveria bassiana.

Three isolates of the entomopathogen Beauveria bassiana along with one strain of Metarhizium anisopliae were cultured on seven media with different carbon/nitrogen (C/N) ratios. The effect of nutrition on virulence of the isolates was evaluated via measurement of colony growth, spore yield, germination speed, conidial C/N ratio and Pr1 (a serine protease) activity. 'Osmotic stress' medium produced the lowest colony growth with low numbers of conidia in all isolates. However, these conidia showed a high germination rate and virulence. However, conidial Pr1 activity was low in some isolates. In most but not in all cases conidia from 1% yeast extract, 2% peptone and low (10 : 1) C/N medium had higher Pr1 activity compared with conidia from other media. However, in some instances we could not conclude that there was a relationship among germination rate, conidial Pr1 activity and virulence. C/N ratio of conidia was statistically different among various media and fungal isolates. Conidia with lower C/N ratio generally produced lower LT(50) (lowest median lethal time) values (more virulent). Insect-passaged conidia from different media had lower C/N ratio compared with similar conidia from artificial cultures. Therefore, they should be more virulent than in vitro produced conidia. As germination rate, conidial Pr1 activity and C/N ratio are independent of host, it seems that host-related determinants such as insect cuticle and physiology and environmental conditions may influence host susceptibility and therefore fungal isolate virulence towards host insects.