Bains NS

Chhuneja P

Dhaliwal HS

Garg T

Kaur S

Keller B

Rawat N

Singh K

Tiwari VK

English

Sydney eScholarship

 1Triticum monococcum: A Source of Novel Genes for Improving Several Traits in Hexaploid Wheat  Singh K1, Chhuneja P1, Kaur S1, Kaur S1, Garg T1, Tiwari VK2, Rawat N2, Bains NS1, Dhaliwal HS2 and Keller B3 1Dept. Plant Breeding, Genetics and Biotechnology, Punjab Agricultural University, Ludhiana, 141004, India. 2Dept. Biotechnology, Indian Institute of Technology, Roorkee, India 3Institute of Plant Biology, University of Zurich, Switzerland  ABSTRACT  The diploid ‘A’ genome progenitor gene pool of wheat, comprising three closely related species T. monococcum ssp monococcum (T. monococcum), T. monococcum ssp aegilopoides (T. boeoticum) and T. urartu, harbours useful genes for many economically important traits, including resistance to diseases and micronutrient content. Their genomes share considerable homology with the A genomes of cultivated tetraploid and hexaploid wheat enabling the transfer of desirable alleles from the ‘non-progenitor’ A genome chromosomes into their ‘cultivated’ homologues without any significant linkage drag. A spring type T. monococcum acc. pau14087 has maintained a high level of resistance to stripe rust, leaf rust, cereal cyst nematode, Karnal bunt and powdery mildew. Using a RIL population generated from a cross of T. boeoticum acc. Pau5088 with T. monococcum acc. pau14087, a linkage map with 179 loci was generated. This population showed segregation for stripe rust, leaf rust, cereal cyst nematode, Karnal bunt, powdery mildew, evolutionary traits like two grains vs one grain per spikelet, and grain iron and zinc content. Using QTL analysis, genes for stripe rust resistance were mapped on 2Am and 5Am; cereal cyst nematode resistance on 1Am and 2Am; evolutionary trait like single vs two grains per spikelet on 1Am and 4Am and high grain iron content on 2Am and 7Am and high grain zinc content on 7Am in diploid species. Putatively novel leaf rust, stripe rust, cereal cyst nematode, Karnal bunt and powdery mildew resistance genes from T. monococcum and T. boeoticum have been transferred to hexaploid wheat cultivars PBW343 and WL711 without any apparent linkage drag. Leaf rust resistance genes transferred from T. monococcum are being mapped in hexaploid wheat background.  BACKGROUND  Wheat, being a major cereal crop, has benefited immensely from global genetic improvement programmes but further improvement in its productivity is being challenged constantly by several biotic and abiotic stresses. Among the biotic stresses, rust diseases are still the most prominent, especially in the Indian subcontinent. For leaf rust, most of the genes identified from the cultivated germplasm are not effective against the prevalent isolates of P. triticina f. spp. tritici in India (Tomar and Menon 2001). Some of the genes transferred from distantly related species have been exploited to some extent, but others seem to be associated with yield penalty due to linkage drag that is difficult to eliminate even after repeated backcrosses once it is selected in the first segregating generation (Young et al 1988). The diploid ‘A’ genome progenitor species Triticum monococcum (AmAm) and T. boeoticum (AbAb) harbour several desirable genes (Dhaliwal et al 1993; Hussien et al 1998) and share considerable homology with the A genomes of cultivated tetraploid and hexaploid wheat (Dvorak et al 1993). Thus, direct hybridization may enable efficient transfer of desirable alleles from the wild species chromosomes into its ‘cultivated’ homologues without any linkage drag. A spring type T. monococcum (acc. 14087) has maintained a high level of resistance to most virulent pathotypes of leaf and stripe rusts over the years (Dhaliwal et al 1993). A recombinant inbred line population (RIL) was developed by crossing T. monococcum (acc. pau14087) and T. boeoticum (acc. pau5088), using the single seed descent method. Using this population, a linkage map with 179 loci was generated (Singh et al 2007). Here we discuss mapping of genes conferring resistance to several diseases and their transfer to the hexaploid wheat background, mapping of evolutionary traits and grain micronutrient density.  STRIPE RUST RESISTACE  Forty genes for stripe rust resistance have been catalogued so far but none has been identified from diploid ‘A’ genome species. T. monococcum (acc. pau14087) and T. boeoticum (acc. pau5088), being maintained at PAU Ludhiana, are susceptible to prevalent stripe rust races at the seedling stage but show resistant reaction at adult plant stage. Genetic analysis of the RIL population revealed the presence of two genes for stripe rust resistance, with one gene contributed by each of the parental lines. QTL analysis of the RIL population led to identification of two QTLs, one each in T. monococcum acc. pau14087 and T. boeoticum acc. pau5088 (Chhuneja et al 2008). The QTL from T. monococcum mapped on chromosome 2A in a 3.6 cM interval between Xwmc407 and Xwmc170 with R2 value of 14%, whereas the QTL from T. boeoticum mapped on 5A in 8.9 cM interval between Xbarc151 and Xcfd12with R2 value of 24%.  These were designated as QYrtm.pau-2A and QYrtb.pau-5A, respectively. T. monococcum acc. pau14087 and three resistant RILs were crossed to hexaploid wheat cvs WL711 and PBW343, using T. durum as a bridging species with the objective of transferring these genes into hexaploid wheat. The B genome of T. durum suppressed resistance in the F1 plants, but with subsequent backcrossing one resistance gene could be transferred from one of the RILs to the hexaploid wheat background. Inheritance studies at the hexaploid level showed that the gene transferred from the RIL is a major gene (Table 1).  2  Table 1. Stripe rust reaction of BC2F3 progenies of the cross N59/RIL101// 3*WL711 (NN) (prgeny#452) and   a BC1F3:4 (derived from a single BC1F3 progeny) of the cross N59/RIL101// 2*WL711 (NN) (Progeny # 480) Progeny ID No. of progenies Total χ2 (1:2:1) HR Seg. HS 452 96 209 118 423 2.34 480 84 157 59 300 4.81 HR = homozygous resistant, HS = homozygous susceptible and Seg. = segregating  LEAF RUST RESISTANCE  At seedling stage, the RIL population showed susceptible reactions against race 104-2, resistant reactions against the race 77-5 but segregated against the race 77-2. However, at adult plant stage, the population showed complete resistance against mixture of the above races, thereby indicating that, in addition to seedling resistance genes, the parents have some common gene that is operative at adult plant stage. The genes showing segregation at seedling stage have not been mapped in the diploid species so far. However, both adult plant and seedling stage resistance genes have been transferred into a hexaploid wheat background and are being mapped. Details can be found in another paper (Kaur et al – in these proceedings).  CEREAL CYST NEMATODE RESISTANCE  Cereal cyst nematode (CCN), Heterodera avenae Woll., is a root nematode of cereals found in more than 31 wheat growing countries of the world (Nicol et al  2003). The effects can be reduced to some extent by crop rotation and chemical and biological control measures, but host plant resistance is the most economically and environmentally sustainable method for managing CCN. So far, only a few sources of resistance viz. Cre1, Cre8 and a QTL QCre.srd-1B have been identified in cultivated hexaploid wheat germplasm. In India, several thousand accessions of bread and durum wheat have been screened against CCN but none of the lines of Indian origin showed any resistance except line AUS15854, from exotic collections, which has a dominant resistance gene and has been used for developing CCN resistant varieties (Sharma et al 2004). Sources of resistance for H. avenae have been identified primarily in wild relatives of wheat. T. monococcum accession 14087 is resistant whereas T. boeoticum acc. 5088 is susceptible to Heterodera avenae (cereal cyst nematode, CCN) population of Punjab. The RIL population showed continuous variation (Figure 1). With composite interval mapping, using the genotypic data of the RIL population (Singh et al 2007), two QTLs, one each on chromosome 1AS and 2AS, conferring resistance to CCN in T. monococcum were identified. The QTL on 1A, designated as Qcre.pau-1A, appeared to be a major gene with 34% contribution to the overall phenotypic variance whereas the QTL on 2A designated as Qcre.pau-2A contributed 12% to total phenotypic variation. Qcre.pau-1A is novel, being the only CCN resistance gene mapped in any ‘A’ genome species and none of the other known genes have been mapped on chromosome 1A. The QTL Qcre.pau-2A, might be allelic to Cre5, a CCN resistance gene transferred from Ae. ventricosa and mapped on 2AS in the same chromosomal region. Qcre.pau-1A was transferred to cultivated wheat using T. durum cv. PBW114 as the bridging species. Selected CCN resistant F8 homozygous introgression lines with 2n=28 and 2n=42 showed the introgression of the molecular markers identified to be linked with CCN resistance locus Qcre.pau-1A indicating that this gene alone reduced cyst multiplication to a threshold level. These introgression lines can be used for marker-assisted transfer of Qcre.pau-1A to elite wheat cultivars.  05101520250-2525-5050-7575-100100-125125-150150-175175-200>200% cysts/pot over the original inoculumNumber of RILs Fig. 1. Distribution of RILs for percent cysts/pot over the initial averaged over two years. Solid arrow indicates percent cyst/pot in T. monococcum and the dashed arrow indicates percent cyst /pot in T. boeoticum.  VARIABILITY FOR EVOLUTIONARY AND PRODUCTIVITY RELATED TRAITS  T. monococcum has, in general, one grain per spikelet whereas T. boeoticum has two grains per spikelet. The RIL population showed variation for grains per spikelet as well. The two accessions also showed variation in grain size with T. monococcum, having bolder seeds compared to T. boeoticum. Data for the traits was recorded for three consecutive years 2005-2007. The QTL analysis (CIM) identified two QTLs, one each on chromosomes 1A and 4A, that govern the grain number per spikelet. The QTL on 1A maps in the region Xcfd65-Xwmc470 and the one on 4A maps in the marker interval Xcfd71-Ba2 (Singh et al 2007) with R2 values of 14.0 and 23.0, respectively. Similarly, for grain weight, two QTLs were identified consistently for all the three years and for the pooled data. The grain weight QTL on 3A maps in the marker interval Xwmc322-Xgwm391, with R2 value of 24.9%, and the QTL on 7A maps in the marker interval RC_A- Xgwm573 with R2 value of 25.3%.   T. monococcum has on average 30-35 spikelets per ear compared to 20-22 spikelets per ear in commercial hexaploid wheat cultivars. One of the RILs with higher spikelets per ear was also crossed to hexaploid wheat  3using T. durum as a bridging species primarily for the purpose of transferring rust resistance into hexaploid wheat. One BC1F3 population derived from a cross N59/RIL130// 2*PBW343 (N59 is a T. durum cultivar whereas PBW 343 is a T. aestivum cultivar) showed segregation for ear size (spikelets per spike). Yield data of about 90 apparently good-looking leaf and stripe rust resistant plants was recorded and compared with the recurrent parent. More than 70% of plants showed higher yields than that of the recurrent parent (Fig. 2) PBW 343. Higher yield in these plants was due to increase in number of spikelets per spike (data not shown). Theses lines are being analysed for introgression from the T. monococcum or T. boeoticum.        Fig. 2. Yield per plant of BC1F3 plants of the cross   N59/RIL130// 2*PBW343. Arrow indicates yield per plant of the recurrent parent PBW 343.  HIGH GRAIN IRON AND ZINC CONTENT  Iron and Zinc are the two micronutrients that are deficient in the diet of people of the third world countries. Iron deficiency ranks among the most widespread nutrient deficiencies, estimated to affect over two billion people worldwide. About 800,000 child deaths worldwide per year are attributable to Zn deficiency in underdeveloped countries. Efforts are under way to increase the Fe and Zn content of major food crops through biofortification. Evaluation of primary and secondary gene pool of wheat showed that T. boeoticum, T. monococcum, T. dicoccoides, Aegilops tauschii and S genome species have a wider range of grain micronutrient density (Chhuneja et al. 2006, Ortiz-Monasterio and Graham 2000). The  T. boeoticum acc. pau5088 used in this study has high Fe (44ppm) and Zn (48ppm) content compared to T. monococcum acc pau14087 that had grain Fe and Zn content of 22ppm and 21ppm respectively. The RIL population also showed significant variation (17-70 ppm for Fe and 17-69ppm for Zn) when evaluated at two locations for two years. QTL analysis using CIM identified two QTL for Fe on chromosomes 2A and 7A   and one for Zn on 7A. High Fe QTLs on 2A and 7A mapped in the marker intervals Xwmc382 - Xbarc124 and Xgwm473 - Xbarc29 respectively and high Zn QTL on 7A maps in the marker region Xcfd31 – Xcfa2079.     REFERENCES Chhuneja  P, Kaur S,  Garg  T, Ghai  M, Kaur  S, Prashar  M, Bains  NS, Goel  R K Keller  B,  Dhaliwal  HS, Singh K (2008) Mapping of adult plant stripe rust resistance genes in diploid A genome wheat species and their transfer to bread wheat. Theor Appl Genet 116:313–324 Chhuneja P, Dhaliwal H S, Bains NS and Singh K (2006) Aegilops kotschyi and Aegilops tauschii as sources for higher levels of grain Iron and Zinc. Plant Breeding 125, 529—531  Dhaliwal HS, Chhuneja P, Singh I, Ghai M, Goel RK, Garg M, Keller B, Röder M, Singh K (2003) Triticum monococcum—a novel source for transfer and exploitation of disease resistance in wheat. In: Proceedings of the 10th international wheat genetics symposium, Paestum, Italy, pp 346–349 Dhaliwal HS, Singh H, Singh KS and Randhawa HS (1993) Evaluation and cataloguing of wheat germplasm for disease resistance and quality. In: Damania AB (ed) Biodiversity and wheat improvement. pp 123-140. John Wiley and Sons Pub. Dvorak J, Terlizzi P, Zhang HB and Resta P (1993) The evolution of polyploidy wheat: identification of the A genome donor species. Genome 36:21–31 Hussien T, Bowden RL, Gill BS, Cox TS, Marshall DS (1997) Performance of four new leaf rust resistance genes transferred to common wheat from Aegilops tauschii and Triticum monococcum. Plant Dis 81:582–586 Nicol, J., Rivoal, R., Taylor, S., and Zaharieva, M. (2003) Global importance of cyst (Heterodera spp.) and lesion nematodes (Pratylenchus spp.) on cereals: distribution, yield loss, use of host resistance and integration of molecular tools. Nematology Monographs & Perspectives 2: 1-19 Ortiz-Monasterio, I, and Graham R D (2000) Breeding for trace minerals in wheat. Food Nutr. Bull. 21, 392—396. Sharma, SN, Saini, RS. and Singh, H (2004) Breeding for resistance to wheat nematode (Heterodera avenae). Acta Agronomica Hungaria 52: 189-197 Singh K, Ghai M, Garg M, Chhuneja P, Kaur P, Schnurbusch T, Keller B, Dhaliwal HS (2007b) An integrated molecular linkage map of diploid wheat based on a Triticum boeoticum X T. monococcum RIL population. Theor Appl Genet 115:301–312 Tomar SMS and Menon MK (2001) Genes for resistance to rusts and powdery mildew in wheat. Pp. 1-52. IARI publication, New Delhi, India Welch, RM and Graham RD (2004) Breeding for micronutrients in staple food crops from a human nutrition prospective. J. Exp. Bot. 55: 353—364 Young ND and Tabksley SD (1989) RFLP analysis of size of chromosomal segment retained around TM-2 locus of tomato during backcross breeding. Theor Appl. Gent. 77: 353-357  0510152015-2020-2525-3030-3535-4040-4545-5050-5555-6060-65yield/plant (g)Number of plants

Triticum monococcum: A source of novel genes for improving several traits in  hexaploid wheat

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Triticum monococcum: A source of novel genes for improving several traits in hexaploid wheat

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