Error bar displays the standard error of the mean. Accumulation of APR genes in accessions improved the level of resistance due to additive gene action. To analyze whether these germplasm accessions perform in a stable way for grain yield in the screening environments, additive mean effects and multiplicative interaction AMMI analysis was carried out. The wheat germplasm closer to the origin of biplot was stable across the four test locations.
The lines connecting the biplot origin and the margins for the environment are called environment vectors. The angle between two environment vectors relates to the correlation coefficient between them. Based on the angles of the environment vectors, locations Powarkheda S2 and Varanasi S4 have relatively good correlation between them, which meant that they are mostly similar in performance.
The Wheat Rusts — Breeding for Resistance
The observation related to length of the environment vector depicts standard deviation within each environment. A critical assessment of biplot revealed that location Pune S3 has large genotype X environmental interaction and greater discriminating power for grain yield followed by Pantnagar S1 , Varanasi S4 , and Powarkheda S2. Germplasm accession viz. The present study was conducted to identify the Indian wheat germplasm accessions carrying APR genes.
Accessions were screened at ten different locations, i. Initially, to select from a large number of accessions, they were evaluated for LTN, a phenotypic trait linked to adult plant leaf rust resistance genes viz.
LTN is characterized by presence of necrosis on flag leaf tips which extend to a few centimetres along the leaf edges [ 27 , 14 ]. Accessions expressed LTN in varying degrees from low to very high. Leaf tip necrosis is considered an innate defense mechanism and is known to occur spontaneously in wheat lines having Lr34 gene [ 28 , 15 ]. While the genetic basis of this mechanism is not clearly understood, it is suggested that Lr34 might some way alter the physiology of flag leaf, thus making it a less desirable for the pathogen to grow and establish [ 29 ].
The use of resistant cultivars for control of wheat rusts
In our study, stable expression of LTN was not noticed; the same accessions expressed different levels of LTN at different locations, thereby confirming the quantitative expression. Low temperature favors the expression of LTN, which is pronounced in accessions grown in cooler locations. Similarly, stronger LTN was observed in seedlings of Lr34 transgenic plants exposed to cold temperature, than untreated plants, which implies that the increase in LTN is due to elevated Lr34 expression levels at low temperature [ 34 ].
It may also have a slight effect in reducing grain yields in some environments [ 35 ].
Breeding cereals for rust resistance in Australia
Inspite of this fact, many high yielding wheat cultivars possess this trait [ 13 ]. In India, wheat growing areas are divided into six zones while the ten locations of our study are located in five wheat cultivation zones except the northern hill zone minor zone. Leaf rust pathotypes 77—5 R 63—1 , R and —2 21R55 are the dominant pathotypes of these zones. In the case of Central zone Vijapur and Powarkheda and Peninsular zone Pune and Dharwad which are either rain-fed or restricted irrigation conditions with dry weather, in addition to pathotypes 77—5 R , R and —2 21R55 ; pathotypes like 77—1 R 63 , 21R and 21R63 are prevalent.
Wellington is the hot spot for leaf and stem rust wherein cool weather prevails throughout the year and the major leaf rust pathotypes are 77—5 R and R Accessions which were resistant to leaf rust, along with LTN in all the locations were selected, which enabled the filtering of accessions from 6, to It has maintained its moderate effectiveness for over 60 years of use [ 37 ]. Dakouri et al. The same could be observed in accessions in the Central and Peninsular zones which have warmer weather; higher leaf rust score was observed in these locations compared to North West and North East Plain Zone and Wellington which are relatively cooler.
Expression of Lr68 depends on temperature wherein lower temperature favors the expression [ 33 ]. Since some of the locations had warm weather, few lines could be identified with Lr It was observed that individually, APR genes do not confer adequate resistance under disease pressure. However, a combination of two APR genes improved the resistance level, while a combination of three APR genes provided a high level of resistance Fig 5 as reported by Singh et al.
Fifty-two accessions were not identified with any of the APR genes evaluated. These accessions were deemed to carry potentially new sources of APR. Of these, nine accessions showed immune reaction while the remaining lines displayed varying levels of resistance. APR genes provide a low level of resistance in field conditions under high disease pressure, so it is possible that lines showing low resistance could carry novel APR genes.
Therefore, to determine whether the resistance is due to novel genes, seedling reaction against prevalent pathotypes followed by mapping is required. The AMMI model is a widely used statistical tool in the analysis of multi-environmental trials. It can be used to understand and structure interactions between genotypes and environments. The AMMI analysis can be very useful in understanding the complex genotype x environment interaction, which includes delineating mega environments or identification of productive cultivars with wide adaptability, as well as delimit the agronomic zoning of cultivars with specific adaptability [ 45 , 46 ].
Accessions with three gene combinations, viz. Therefore, they can be used as parents for the introgression of APR genes without compromise on yield or with minimal linkage drag. These accessions are adapted to specific areas which can be used for the improvement of cultivars of particular locations. Accessions displayed diverse disease reaction, i. This is due to the fact that APR gene expression is sensitive to environmental conditions, because of: firstly, the quantitative nature of the resistance; and secondly, the genetic background of the germplasm.
The purpose of durable resistance based on minor genes is to remain effective in a cultivar during its widespread cultivation for a long sequence of generations or period of time, in an environment favorable to a disease or pest [ 47 ]. These accessions were collected from previously mentioned wheat cultivated regions of India wherein leaf rust is a common problem. These collections include land races, old cultivars, obsolete varieties, cultivars, etc.
For thousands of years, wheat cultivation has been practiced in this region but it has also created the opportunity and conditions for the rust pathogen to co-evolve with wheat. Lr13 , Lr23 , Lr24 , Lr26 , etc. So, when these germplasm lines were subjected to molecular marker analyses, presence of APR gene got detected. After achieving a certain level of resistance, nature of gene is more important rather than number of genes. APR genes, Lr34 , Lr46 and Lr67 have been studied extensively and it had pleiotrophic association with stem and stripe rust resistance, i.
Presently, it is being extensively used in the wheat improvement program in India and worldwide.
Stripe Rust: A Review of the Disease, Yr Genes and its Molecular Markers
However, the eight germplasm accessions with three and two APR gene combinations having wider adaptability could be exploited for broadening the genetic base of the cultivated wheat to provide durable resistance. Closely linked molecular markers could be useful in the marker assisted selection or mobilization of these genes in elite wheat backgrounds. Improvement of any crop lies in exploring and exploiting the rich gene pools available in its cultivated forms, land races, wild relatives and related genera. The conservation of a resource only becomes important if the resource has or acquires recognized value.
This study highlights the importance of wheat germplasm in providing a durable solution for the evolving rust pathogen. Availability of robust and diagnostic molecular markers for the APR genes would speed up the process of durable rust resistance breeding. Accessions deemed to potentially carry new sources of APR genes require more detailed study.
Rust pathogens have the ability to evolve new pathotypes rapidly with high reproductive rate and to spread quickly are a major threat to food security. Screening and deployment of genes warrants searching for additional genes, which confer race non-specific resistance to provide durable resistance. Germplasm collected from different agro-ecological regions at different points of time provide an opportunity to bio-prospect for such genes. The genetic base for leaf rust resistance among cultivars could be broadened and diversified through the use of resistant accessions identified in the study as donors in wheat improvement programmes.
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Abstract Leaf rust Puccinia triticina Eriks. Screening of wheat germplasm for the presence of LTN trait and leaf rust reaction Germplasm lines were screened under field conditions and using artificial inoculation for the presence of LTN, a phenotypical trait linked to the APR genes, along with leaf rust reaction, at ten locations in India for two years. Download: PPT. Table 1. Avirulent and virulent profile of pathotypes prevalent in the tested locations. Stability analysis Stability analysis of 49 promising lines with two and three APR gene combinations were performed for grain yield under four different environments viz.
DNA marker analyses. Table 2. Fig 1. Table 3. Highest score HS and average coefficient of infection ACI based on leaf rust reaction of germplasm accessions at 10 locations. Fig 2. Mean leaf rust infection of wheat accessions grown at 10 different locations across the climatic zones of India. Molecular marker screening for APR genes Accessions selected based on LTN and leaf rust reaction were further subjected to molecular marker confirmation for the presence of known APR genes viz.
Fig 3. Distribution of APR genes among the selected wheat accessions. Fig 4. Effect of temperature on the effectiveness of different APR genes against leaf rust severity. Fig 5.
Leaf rust reaction with respect to number of APR genes in wheat accessions. Fig 6. AMMI biplot showing stability of promising genotypes across four environments for grain yield.
Discussion The present study was conducted to identify the Indian wheat germplasm accessions carrying APR genes. Conclusions Rust pathogens have the ability to evolve new pathotypes rapidly with high reproductive rate and to spread quickly are a major threat to food security. Supporting information. S1 Table. Passport data of leaf rust resistant Indian wheat accessions.
S2 Table. Adult plant resistance APR genes in the leaf rust resistant accessions. S1 Fig. References 1. Food and Agriculture Organization. Accessed 15 June Food Agric.