2009 Annual Report
1a.Objectives (from AD-416)
Fusarium head blight (FHB) or scab,caused by the fungus Fusarium graminearum Schwabe, is a serious disease of wheat. The research objective is to develop genetic resistance to FHB in durum, or macaroni, wheat (Triticum turgidum L., 2n = 4x = 28; AABB genomes) by exploiting novel sources of resistance in the wild relatives. It has been difficult to identify effective sources of resistance in durum wheat cultivars. However, several wild grasses, including diploid wheatgrasses in the secondary or tertiary gene pool of wheat, are excellent sources of FHB resistance that may be incorporated into durum germplasm. Improved durum germplasm with reliable FHB resistance could then be used to incorporate resistance genes into durum and bread wheat cultivars.
Specific subobjectives of this project are to:
a. Develop alien addition lines involving chromosomes or chromatin, with FHB resistance from diploid wheatgrasses, Lophopyrum elongatum (Host) Á. Löve [= Agropyron elongatum (Host) Beauv.] and Thinopyrum bessarabicum (Savul. & Rayss) Á. Löve (= Agropyron bessarabicum Savul. & Rayss).
b. Initiate new crosses with other potential donors such as Thinopyrum junceiforme (Löve & Löve) Löve, 2n = 4x = 28; J1J1J2J2 genomes) and Thinopyrum nodosum [= Lophopyrum nodosum (Nevski) Á. Löve] that may provide new sources of alien chromosomes with FHB resistance.
c. Characterize the added alien chromosome(s) from the wild relatives that confer FHB resistance to durum wheat.
d. Evaluate both FHB resistance and mycotoxin deoxynivalenol (DON) accumulation with the longer-term objective of releasing FHB-resistant germplasm.
e. Assess the genomic relationships between wheat and related species in the intergeneric hybrids.
1b.Approach (from AD-416)
Alien gene transfer into durum wheat will be carried out by tools of classical and molecular cytogenetics. The cytogenetic techniques will involve sexual hybridization between durum cultivars and wild grasses,coupled with induction of pairing among chromosomes of parental species by manipulation of the pairing-control mechanism(Ph1). This approach will facilitate transfer of alien chromatin into the durum genome, which will then be characterized using fluorescent genomic in situ hybridization (fl-GISH) and chromosome-specific markers. Using this approach, alien addition lines involving diploid wheatgrass (Lophopyrum elongatum and Thinopyrum bessarabicum) chromosomes or chromatin with FHB resistance will be developed. In addition to using these two diploid wheatgrasses as donors of FHB resistance, we will initiate new crosses with other potential donors such as Thinopyrum junceiforme and Thinopyrum nodosum (= Lophopyrum nodosum) that may provide new sources of alien chromosomes with resistance. Fertile hybrid derivatives and stable alien addition lines will be screened for FHB resistance using the techniques we have already standardized.
Current durum cultivars have little or no resistance to Fusarium head blight (FHB). Some of the wild grass species have excellent resistance to this ravaging disease. Therefore, we crossed durum cultivars with the wild grasses and selected fertile hybrid derivatives with FHB resistance. In order to reduce the number of alien chromosomes we isolated addition lines with the chromosome conferring the most FHB resistance. From the crosses between durum cultivars Langdon and Lloyd with the alien species Lophopyrum elongatum and Thinopyrum bessarabicum, we isolated several addition lines with 2n = 29 and 2n = 30 chromosomes. We isolated FHB-resistant disomic addition lines involving L. elongatum chromosomes. After confirming the somatic and meiotic chromosomes we characterized the added alien chromosome using chromosome-specific markers. The alien chromosome in the FHB-resistant durum disomic alien addition line is 1E.
Following the same approach we isolated several hybrid derivatives of Lloyd x Th. bessarabicum with chromosome numbers ranging 2n =29 to 2n = 33. These derivatives were advanced by single seed descent (selfing) and we isolated alien additions with 2n = 29 and 2n = 30 chromosomes.
Once we had an appropriate addition line with FHB resistance we wanted to know the identity of the chromosome involved. To characterize the added Th. bessarabicum chromosome we used specific molecular markers, some of which had been determined to be specific to L. elongatum chromosomes. Sixteen Xedm primers and twelve Xgwm primers were used that tentatively identified Th. bessarabicum chromosomes 1, 6, and 7. Further study is in progress to identity each of the 7 alien chromosomes.
To transfer the desirable gene(s) from the alien chromosome into the durum complement, we made crosses between DGE-1 and Cappelli ph mutant. F1s of the DGE-1 x Cappelli ph mutant were grown to generate seed. Chromosome pairing was scored in the F2 generation which would be the first generation without Ph1 in the segregating population.
Chromosome pairing in the F1 hybrids between DGE-1 and the Langdon substitutions was studied to assess the pairing between the added alien chromosome 1E and group-1 homoeologous chromosomes of Langdon.
Jauhar, P.P., Xu, S.S., Baenziger, S. 2009. Haploidy in Cultivated Wheats: Induction and Utility in Basic and Applied Research Crop Science Vol 49:737-754
Jauhar, P.P., Peterson, T.S., Xu, S.S. 2009. Cytogenetic and Molecular Characterization of Durum Alien Disomic Addition Line with Enhanced Tolerance to Fusarium Head Blight Resistance. Genome 52:467-483.