Wheat powdery mildew (Blumeria graminis f. sp. tritici) has increased in Delta Egypt in recent years as a result of growing susceptible cultivars of bread wheat. Fifty-two isolates of B. graminis f. sp. tritici collected in 2013 and 2014 from commercial fields in five provinces were analyzed for virulence, using 21 genes conferring resistance to powdery mildew (Pm genes) as well as 12 local wheat cultivars. First true leaves of 10-day-old wheat differentials were inoculated with isolates derived from a single pustule of B. graminis f. sp. tritici. No virulence to the resistance genes Pm3d, Pm12, Pm16, Pm24, Pm35, Pm36, and Pm37 was detected, indicating that these genes could be used for resistance breeding. Virulence to Pm2, Pm4a, and Pm6 was low, while high virulence to genes Pm1a, Pm3a, Pm3c, Pm3f, Pm5a, Pm7, Pm8, Pm9, and Pm17 was found, indicating that breeders should be very cautious in using these genes. At the adult stage, genes Pm2, Pm3d, Pm3f, Pm4a, Pm6, Pm12, Pm16, Pm17, Pm24, Pm35, Pm36, and Pm37 were completely effective in both years. All the tested Egyptian wheat cultivars were susceptible under natural field conditions. The virulence of B. graminis f. sp. tritici population and resistance Pm genes have been assessed for the first time in Egypt.

BackgroundThe main aim of this study was to improve fungal resistance in bread wheat via transgenesis. Transgenic wheat plants harboring barley chitinase (chi26) gene, driven by maize ubi promoter, were obtained using biolistic bombardment, whereas the herbicide resistance gene, bar, driven by the CaMV 35S promoter was used as a selectable marker.ResultsMolecular analysis confirmed the integration, copy number, and the level of expression of the chi26 gene in four independent transgenic events. Chitinase enzyme activity was detected using a standard enzymatic assay. The expression levels of chi26 gene in the different transgenic lines, compared to their respective controls, were determined using qRT-PCR. The transgene was silenced in some transgenic families across generations. Gene silencing in the present study seemed to be random and irreversible. The homozygous transgenic plants of T4, T5, T6, T8, and T9 generations were tested in the field for five growing seasons to evaluate their resistance against rusts and powdery mildew. The results indicated high chitinase activity at T0 and high transgene expression levels in few transgenic families. This resulted in high resistance against wheat rusts and powdery mildew under field conditions. It was indicated by proximate and chemical analyses that one of the transgenic families and the non-transgenic line were substantially equivalent.ConclusionTransgenic wheat with barley chi26 was found to be resistant even after five generations under artificial fungal infection conditions. One transgenic line was proved to be substantially equivalent as compared to the non-transgenic control.Electronic supplementary materialThe online version of this article (doi:10.1186/s13007-017-0191-5) contains supplementary material, which is available to authorized users.

Wheat powdery mildew, caused by the biotrophic fungus Blumeria graminis (DC) E.O. Speer f. sp. tritici Em. Marchal, is one of the most severe foliar diseases attacking this crop, affecting wheat production under Mediterranean basin conditions through the last few years. Four bread wheat cultivars i.e.. Sakha-93, Gemmeiza-7, Gemmeiza-10, and Giza-160 as a check were evaluated to artificial inoculation of powdery mildew under field conditions. The tested wheat cultivars showed susceptible responses to powdery mildew with fluctuated values in 2010 and 2011 seasons. In 2010 season, the tested cultivars showed high levels of disease severity, ranged from 35 to 87 % (Gemmeiza-7 and Gemmeiza-10, respectively). While, in 2011 lower levels were recorded, from 6.00 up-to 15% (Sakha-93 and Gemmeiza-10, respectively). Area under disease progress curve (AUDPC) was correlated with disease severity during the two seasons. Also, the yield components, the thousand grain weight and the grain yield/m 2 were affected by disease severities with different values for each cultivar. High air temperature, wind speed and mild relative humidity played an important role in increasing powdery mildew infection level in 2010 season.

Powdery mildew of wheat (Triticum spp.) caused by Blumeria graminis f.sp. tritici (DC) E.O. Speer Em. Marchal is one of the most important bread wheat diseases in Egypt. All the Egyptian common bread wheat cultivars are susceptible to that disease at seedling and adult stages. Breeding of resistant cultivars is the most economical and environmentally safe method to eliminate the disease and reduce crop losses. Combinations of two or more effective resistance genes may lead to better, more durable resistance to that disease. Eight Pm genes i.e. Pm2, Pm6, Pm12, Pm16, Pm24, Pm35, Pm36 and Pm37 out of 21 powdery mildew monogenic wheat lines (Pm) were resistant to 42 individual isolates of powdery mildew collected from different governorates in the Nile Delta area, Egypt, at seedling and adult stages. Only four DNA specific SSR markers (Xgwm337, Xcfd7 linked to Pm24, Pm35 and Xgwm332, Xwmc790) linked to Pm37 resistance genes were selected to detect these genes in 13 Egyptian common bread wheat cultivars. This study reveals the absence of Pm24, Pm35 and Pm37 in all the 13 Egyptian bread wheat cultivars. These results gave evidence that the Egyptian cultivars are not having resistance genes and need to further incorporate one, two or more resistant genes in a single genotype as all commercial cultivars defeated by the pathogen.

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