RESUMO
Since the emergence of Ug99 wheat stem rust in Uganda in 1998 (Pretorius et al. 2000), the threat of movement into South Asia has been a concern due to long-distance dispersal capacity of airborne spores (Brown and Hovmøller 2002; Singh et al. 2008; Meyer et al. 2017). Increased preparedness by comprehensive rust surveillance efforts and development and deployment of resistant cultivars in advance of an incursion into South Asia has been one of the success stories of the Borlaug Global Rust Initiative (Sharma et al. 2013). In November 2023, an off-season rust survey was conducted in Marpha, Gandaki and Bagmati provinces in Nepal. Rust was only observed at two sites, Dangdunge of Dolakha district and Mude of Sindhupalchok district, where spring wheat was grown as fodder crop outside the main cropping season. Rust infected wheat leaves (10-15 leaves per site) were air dried and sealed in envelopes that were shipped under permit to the Global Rust Reference Center, Denmark. Bulk samples of stem rust, Puccinia graminis f.sp. tritici (Pgt), were recovered from both envelopes, and single pustule isolates were raised and multiplied on Morocco and McNair. Meanwhile, specimens of dry leaves were subjected to SSR genotyping according to standard procedures (Patpour et al. 2022). One distinct multi-locus Pgt genotype was observed, identical to and representing 99% of Ug99 isolates within Clade I collected in East Africa between 2012-2022. A Pgt single pustule isolate from each of the sampling sites were inoculated onto 20 internationally agreed stem rust differential lines using standard procedures, and 14 supplementary lines providing additional resolution of pathogen virulence (Patpour et al. 2022). The pathotyping was repeated in two independent experiments, which resulted in the infection type pattern of Pgt race TTKTT (Supplementary Table 1). Additional independent SSR genotype assays of recovered isolates confirmed the prevalent genotype of Clade I (Patpour et al. 2022; Szabo et al. 2022). This first detection of Ug99 race TTKTT in South Asia emphasizes the need for continued coordinated international surveillance efforts and utilization of diverse sources of resistance to control stem rust in wheat. New surveillance efforts in Nepal during February-March 2024 did not reveal additional cases of wheat stem rust. However, more detailed and sustained rust surveillance efforts, assessment of the vulnerability of current wheat crops to Ug99 and other races of stem-, stripe/yellow- and leaf rust, as well as intensified breeding for rust resistance throughout the region is strongly recommended to meet current and future plant health risks.
RESUMO
Wheat (Triticum aestivum L.) is one of the major staples in Nepal providing the bulk of food calories and at least 30% of Fe and Zn intake and 20% of dietary energy and protein consumption; thus, it is essential to improve its nutritional quality. To select high-yielding genotypes with elevated grain zinc and iron concentration, the sixth, seventh, eighth, and ninth HarvestPlus Yield Trials (HPYTs) were conducted across diverse locations in Nepal for four consecutive years: 2015-16, 2016-17, 2017-18, and 2018-19, using 47 biofortified and 3 non-biofortified CIMMYT-bred, bread wheat genotypes: Baj#1, Kachu#1, and WK1204 (local check). Genotypic and spatial variations were found in agro-morphological traits; grain yield and its components; and the grain zinc and iron concentration of tested genotypes. Grain zinc concentration was highest in Khumaltar and lowest in Kabre. Likewise, grain iron concentration was highest in Doti and lowest in Surkhet. Most of the biofortified genotypes were superior for grain yield and for grain zinc and iron concentration to the non-biofortified checks. Combined analyses across environments showed moderate to high heritability for both Zn (0.48-0.81) and Fe (0.46-0.79) except a low heritability for Fe observed for 7th HPYT (0.15). Grain yield was positively correlated with the number of tillers per m2, while negatively correlated with days to heading and maturity, grain iron, grain weight per spike, and thousand grain weight. The grain zinc and iron concentration were positively correlated, suggesting that the simultaneous improvement of both micronutrients is possible through wheat breeding. Extensive testing of CIMMYT derived high Zn wheat lines in Nepal led to the release of five biofortified wheat varieties in 2020 with superior yield, better disease resistance, and 30-40% increased grain Zn and adaptable to a range of wheat growing regions in the country - from the hotter lowland, or Terai, regions to the dry mid- and high-elevation areas.