The present challenge in wheat breeding is to decipher the molecular mechanisms of heat stress response and thermotolerance in detail for future applications. Several reports indicate the ability of plants to maintain a memory of stress exposure throughout their ontogenesis and even transmit it faithfully to the following generation. Here, three diverse genotypes of wheat viz., HD2967, WR544 and C306 were used for thermotolerance assays. The genotype HD2967 was able to withstand heat stress regimes (37?C and 42?C, 2 hours). Harvested seeds were sown and further raised for two consecutive years and phonotypical data evaluated in natural field condition by exposing to heat stress during generative stages in a heat trap chamber. Maximum tiller numbers and flag leaf length were noticed in second generation plant of 37?C heat exposure whereas flag leaf width in second generation 42?C heat exposure relative to the untreated plant. Auricle length showed no difference but plant height was notably increased in the second year in all the heat exposed plants. In grain yield index, ear head length was greater in the second year and fluctuations in grain number was noticed among the heat treated plant with more yields in 42?C and 42?C HTHT in the second year. IRGA and SPAD recording showed high photosynthesis and chlorophyll content in 37?C HTHT. High modulation of transcripts of several genes involved in DNA methylation and heat stress were also observed. The domino effect of heat stress in earlier generation, in this transgenerational analysis, points towards a probable epigenetic effect. Further studies are in progress to confirm and clarify the mechanisms for future manipulation in breeding for thermotolerance.
Durum wheat is the tenth most important crop in the world, but its cultivation is mostly limited to harsh, arid, and heat prone marginal lands. Breeding for tolerance to these conditions is often considered the most strategic approach to ensure adaptation, especially when paired with best agronomical practices. The word 'adaptation' summarizes all the research efforts conducted to identify the many traits controlling the mechanisms for withstanding or escaping the traceries of the environment. It can be summarized as "GGE vs E". The durum wheat breeding program of ICARDA deploys targeted phenotyping methods in combination with genomic scans to dissect these 'adaptive' traits into simple loci. These loci can then be pyramided via a combination of international field testing, markers assisted selection, genetically-driven crossing schemes, and genomic selection to derive climate-ready cultivars. Here, several examples of this approach are presented and their implications for 'adaptation' are discussed.
Frontline demonstrations (FLDs,) on wheat were conducted by Agharkar Research Institute, Pune, during last five rabi seasons from 2012-13 to 2016-17 at farmer's fields of Pune and Satara district under wheat growing area of semi-arid tropics of western Maharashtra, India. Before conducting FLDs, a group meeting held every year in the selected village and specific skill training had imparted to the randomly selected farmers regarding adoption of different improved aspects of cultivation. FLDs comprised of improved wheat varieties viz., MACS 6222, MACS 6478, MACS 3125 (d) and MACS 2971(dic) for Peninsular Zone of India. About 50 ha of FLDs on improved wheat varieties were conducted with active participation of 50 farmers covered an average of 10 farmers and 10 ha per year. Two recent varieties, MACS 6222 and MACS 6478 had shown higher grain yield, ranging between 15 to 55 per cent more over local check and farmer practice than all other FLDs. Recommended packages and practices of wheat FLDs gave higher value of yield, net return and high benefit cost ratio as compared to local check over the years of study. The study has revealed that five years mean extension gap of 4.48 to 9.67 q/ha and technology gap ranging between 11.00 to 22.22 q/ha depending on the variety during the period of study. Net returns of Rs. 63042/ha was observed from improved practice than in the farmer's practice of Rs. 50108/ha and with benefit cost ratio of 3.07 and 2.79 respectively. On average basis, the incremental benefit cost ratio was found as 2.83. In frontline demonstrations, the yield potential of wheat has been enhanced largely due to the increase in the knowledge of farming community and adoption of improved production techniques by farmers.
Primary Author: Baviskar, Agharkar Research Institute Pune
The Lr34/Yr18 gene has been used in agriculture for more than 100 years. In contrast to many other resistance sources against leaf rust and stripe rust, it has remained effective and no virulence has been reported. This makes Lr34 a unique and highly valuable resource for rust resistance breeding. The pleiotropic nature of the gene conferring partial resistance to different pathogen species, the associated leaf tip necrosis and its durability suggest a molecular mechanism that is different from major gene resistance. This is supported by the molecular nature of Lr34 which was recently found to encode an ABC transporter. Interestingly, all tested wheat lines contain an allele of the Lr34 gene on chromosome 7DS. In its susceptible form, the gene does not confer resistance. The difference between the encoded resistant and susceptible LR34 isoforms consists of only two amino acid changes, whereas the rest of the proteins are identical. These two changes must change the biochemical properties of the resistant LR34 transporter in such a way that the plant becomes resistant. We speculate that there is a slight conformational change in the resistant form of the protein, resulting either in modified specificity or kinetics of the transported molecule, or that the binding properties to an unknown second protein interacting with LR34 are changed, resulting in altered function. While the molecular nature of the molecule(s) transported by the LR34 protein remains unclear, it is likely that a physiological change related to Lr34 activity is at the basis of resistance. We are currently establishing transgenic approaches in heterologous grass species to further investigate the molecular activity of Lr34 and to better understand a physiological mechanisms resulting in disease resistance.
Primary Author: Beat Keller, Institute of Plant Biology, University of Zurich, Switzerland
CIMMYT wheat germplasm flow to Ethiopia started in the late 1960s. Over 90 bread wheat varieties were released over the decades. Of these, about 77% had CIMMYT origins or were derived from CIMMYT materials. Wheat is a traditional rainfed crop grown by 5 million small-scale farmers on 1.6 ha more or less. Yields have increased from 1.0 t/ha in the 1960s to 2.54 t/ha in 2014 mainly due to high yielding semi-dwarf bread wheat varieties and modern agronomic practices. Using such technologies, better farmers often get 5-6 t/ha. The rusts are the most important production constraints. For example, the 2010 yellow rust epidemic debilitated the mega varieties Kubsa and Galama in the highlands. In 2013/14, stem rust caused up to 100% yield losses in the widely adopted bread wheat variety Digalu in Arsi and Bale. This epidemic was caused by Pgt race TKTTF, which is virulent to the gene SrTmp that is present in Digalu, but is avirulent to Sr31, which is overcome by race Ug99 (TTKSK) and derivatives. To avert the increasing threat of rusts, CIMMYT developed a shuttle breeding program where germplasm moves back and forth between Mexico and Kenya and has increased nursery testing sites (Holetta, Kulumsa, Debre Zeit, Sinana, Adet, and Melkassa) in Ethiopia from two to six. The germplasm passes through rigorous tests against major diseases during both the main- and off-seasons. To obtain high yielding rust resistant germplasm, many hundreds of genotypes were introduced and tested over the last two years. In 2014/15, 266 (25%) lines with multiple disease resistances and high yield were promoted to national trials. CIMMYT continues to be an important source of germplasm. Fast tracked variety testing and release, accelerated seed multiplication, demonstration and popularization of new varieties with high yield, multiple disease resistance, and acceptable quality will continue.
In 2010, Ethiopia experienced one of the largest stripe rust epidemics in recent history. Over 600,000 ha of wheat were affected, an estimated 60 million Ethiopian Birr ($US3.2 million) were spent on fungicides and large production losses were observed. Factors associated with the 2010 epidemic were conducive climatic conditions (prolonged rain and apparently optimal temperatures), large areas planted to susceptible cultivars, early infection and rapid spread of a virulent pathogen, a low level of awareness, and ineffective control measures. In 2013, highly favourable climatic conditions and early appearance of stripe rust showed remarkable similarity to the conditions observed in 2010, prompting fears of a similar major rust epidemic. However, no stripe rust epidemic developed in 2013. In contrast, only limited and localized outbreaks of stripe rust were observed in 2013; wheat crops remained in good condition and a good harvest was achieved. It seems that a series of positive and timely actions in Ethiopia contributed to the markedly different stripe rust situation in 2013 compared to 2010. The principle factors associated with the positive outcomes in 2013 are (i) effective promotion, plus rapid and widespread adoption of rust resistant wheat cultivars since 2010 - this dramatically reduced the vulnerability of the Ethiopian wheat crop; and (ii) timely and coordinated surveillance efforts, coupled to good information exchange amongst different stakeholders - this resulted in effective control and awareness campaigns that targeted emerging stripe rust outbreaks. A comparative analysis is presented which highlights the similarities and disparities between the 2010 and 2013 stripe rust situations in Ethiopia. The roles and contributions of different organisations are examined and an in-depth analysis of the biophysical conditions in the different years is presented.
The most serious wheat diseases affecting yield and quality in West Transitonal Zone of Turkey is rust diseases. Breeding resistant varieties is the most economic and confident way to struggle with these diseases. In this study, it was aimed to determine the genotypes which are resistant to stripe and stem rust diseases existing in our region and use these genotypes as material in breeding program. The study was carried out in 2014 at natural and artificial epidemic conditions in the experimental field of Transitional Zone Agricultural Research Institute. The reactions of some wheat genotypes to stripe and stem rust diseases caused by the fungal agents P.striformis ve P.graminis were detected. For this purpose, 310 lines and 18 variety of bread wheat belonging to Transitional Zone Agricultural Researh Institute were sown in a way 1 m x 1 row. The disease assessments were conducted in May-June 2014 according to the Modified Coob Scale. As a result of infection coefficient observations, it was determined that 49% of the material are resistant to stripe rust and 60% of the material are resistant to stem rust.
Primary Author: Belen, Transitional Zone Agricultural Research Institute, Turkey
Septoria tritici blotch disease, caused by the fungus Zymoseptoria tritici, is a major threat to global wheat production. With the recent advances in high-throughput DNA-based technologies, Z. tritici has become a powerful model system for the discovery of candidate determinants that underlie virulence and host specialization. Although a few important virulence/regulatory genes have been identified, a global understanding of the larger regulatory network has not been developed. Therefore, to uncover the transcriptional regulatory networks of the infection cycle and most particularly the regulatory hubs that control the switch between the biotrophic and necrotrophic phases, we applied an integrated approach combining transcriptomics, proteomics, and metabolomics analyses based on the identification of plant and fungal transcription factors and regulators, which we characterized from the newly annotated genome sequence of the reference isolate IPO323 (Grandaubert et al., 2015) and using datasets from Rudd et al. (2015). Bread wheat transcription factors and regulators were identified by querying the proteome and subsequent categorization from the Plant Transcription Factor database (PTFDB). Similarly, Z. tritici transcription factors and regulators were identified and categorized using the PFAM TF family databases, and following fungal transcription factor rules as outlined by Todd et al. (2014) and rules we developed for fungal transcription regulators. Insights into transcription factors and regulators will enable synthetic biology approaches to alter the Z. tritici-wheat interaction and lead to rewiring of the regulatory networks thereby turning off the fungal infection process. Beyond providing insights into the regulatory systems-levels involved in Z. tritici-wheat interaction, we believe that our dataset and approach sets the stage for an emerging series of studies that will decipher the dynamic regulatory networks in other plant-pathogen interactions.
Primary Author: Ben M'Barek, Laboratory of Molecular Plant Physiology, Biotechnology Center of Borj Cedria (CBBC)
Among the many biotic constraints to wheat production in Algeria, rusts and in particular yellow rust (Puccinia striiformis), are among the most prevalent diseases that occur mostly all over the northern part of the country. Yellow rust has become now sporadic due to the exploitation of effective resistant genes in different forms and combinations (from CIMMYT and ICARDA). Earlier, durable resistance was probably due to many genes, such Yr18, Yr9, Yr27 and Yr1.
Yellow rust appeared as epidemic in 2004, over 600 000 ha of bread wheat ; severity exceeded 70%. Yields from affected fields of Hidhab a susceptible variety did not exceed 5.2 q/ha, while resistant cultivars yielded up to 48 q/ha. Monitoring of the pathogen virulence factors and their changes provides basic information for the development of an early warning system. This experiment was carried out in 5 Eastern Algeria locations. 30 lines of a standard set of yellow rust and 14 near-isogenic lines from ICARDA were sown in 2-m rows in 2014 and 2015. According to the results, virulence on Heines Kolben (Yr2), Kalyansona (Yr2), Lee (Yr7), Avocet R (YrA), Federation*4/Kavkaz (Yr9), Yr6/6*Avocet ?S?, Yr7/6*Avocet ?S?, Yr9/6*Avocet "S", Yr17/6*Avocet "S", TP1295 (Yr25) and YrSU was common during those two seasons. The frequency of virulence on plants with Yr2, Yr6, Yr7, Yr9 or YrA and Yr27 was up to 80%. No virulence was observed on plants with Yr1, Yr3, Yr4, Yr5, Yr8, Yr10, Yr15 and Yr18 genes. This material was extensively used in our breeding programs and several new cultivars are in the on farm trials where a participatory selection approach is used. All resistant and performing new varieties are being spread for replacement of most old susceptible ones.
Primary Author: Benbelkacem, National Agronomic Research Institute of Algeria
In the context of climate change, drought is one of the most important and complex abiotic stresses affecting crop production worldwide. The adoption of an appropriate technological package, principally drought tolerant varieties, may overcome these challenges to meet global food security needs for the rapidly growing human population, particularly in developing countries. Therefore, this research was carried out to identify efficient phenotypic and genetic selection criteria to identify drought tolerant wheat varieties. In this perspective, 200 diverse elite bread wheat lines from ICARDA and CIMMYT were evaluated under four Moroccan environments during the 2015 and 2016 seasons for yield and 15 agro-physiological traits. The same set of genotypes was genotyped using 15k SNPs. Significant environment and genotype environment interaction effects were observed for yield. Average yield reached 3.18t/ha and ranged from 2.45 to 4.27t/ha. The secondary traits were mostly dominated by the environment effect (p<0.001). Based on correlation and regression analysis between grain yield and phenotypic data, the biomass, grain number per m<sup>2</sup> and to a lesser extent fertile spikes number and thousand kernel weights (depending of drought scenarios) can be more reliable traits than yield for the identification of drought tolerant genotypes. Moreover, the ground cover and canopy temperature depression can be used as supplementary criteria for more accurate selection. Slow selection on the basis of phenotypic traits may be accelerated and improved by using molecular markers. The genetic analysis highlighted significant SNPs and identified new QTLs linked to yield and the most efficient phenotypic traits under drought conditions. These findings could be useful for breeding drought-resistant wheat cultivars using marker-assisted selection to accumulate these favorable alleles of SNPs associated with yield-related traits to increase grain yield.
Primary Author: Bennani, National Institute of Agricultural Research