Utilization of Aegilops geniculata Diversity in the CIMMYT Wheat Program

Among the 22 species of the genus Aegilops, Aegilops geniculata Roth (syn.= Ae. ovata L.) is particularly interesting as a source of resistance to diseases and pests (Friebe and Heun, 1989) and tolerance to drought and salinity (Rekika et al., 1998). This suggests that the species may be a valuable reservoir of genes for improving wheat resistance to both biotic and abiotic stresses.

Ae. geniculata (Fig. 1) is an annual, self-fertile, allo-tetraploid species (2n=4x=28) with MU genome (Van Slageren, 1994). It is widely distributed around the Mediterranean region.

A collection comprising 160 Ae. geniculata accessions originating from different eco-geographical regions (Fig. 2) was established. Their genetic diversity was analyzed on the basis of molecular markers (RAPD, RFLP) and morphological traits (Zaharieva et al., 1999; Zaharieva et al. 2001b)(Fig. 3).

Fig. 2. Origin of Aegilops geniculata accessions

Fig. 3. Management of Aegilops geniculata resources

Resistance to barley yellow dwarf virus, rusts, and cereal cyst nematodes has been identified in the collection (Zaharieva et al., 2000). The accessions were evaluated for resistance to leaf and stripe rusts and root lesion nematodes at CIMMYT. The collection was also studied for physiological traits related to drought and heat stress (Zaharieva et al., 2001a). A set of promising accessions possessing resistance traits was then selected for use in our wide hybridization program (Table 1).

Resistant Ae. geniculata accessions were crossed with susceptible high-yielding bread and durum wheats (Table 2) with priority currently given to transfers for BYDV resistance. F1 hybrids produced have been cytologically analyzed and validated to be n=5x=35 (ABDUM) or n=4x=28 (ABUM). For each cross, some F1 hybrids shall be doubled and amphiploids evaluated for the targeted diseases. The other F1 hybrids will be backcrossed to the wheat parents for advancing the desired cross combination (Fig. 4). A crossing program is also underway to hybridize Chinese Spring (phph) and Capelli (ph1c) with Ae. geniculata accessions and promote F1 homoeologous pairing. A parallel strategy will be utilized in bread wheat-based F1 hybrids or amphiploids where a backcross of these materials will be made by Chinese Spring phph and advanced using the protocol of Mujeeb-Kazi (1998).

Molecular markers will also be used to follow the introgressed alien material. Microsatellite DNA markers detecting genetic differences even among closely related individuals are useful for characterizing Triticum and Ae. geniculata genotypes and their progenies. Furthermore, molecular markers related to resistance traits or genes coming from the wild species could be explored.

Fig. 4a. Sheme of alien transfers from Aegilops geniculata to Triticum aestivum via the addition line production route

Fig. 4b. Sheme of alien transfers from Aegilops geniculata to Triticum durum via the addition line production route

Friebe B., Heun M. 1989. C-banding pattern and powdery mildew resistance of Triticum ovatum and four T. aestivum -- T. ovatum chromosome addition lines. Theor. Appl. Genet., 78, 417-424.

Mujeeb-Kazi A. 1998. An analysis of the use of haploidy in wheat improvement. In Kohli M.M. and Francis M. (eds) Application of Biotechnologies to Wheat Breeding. La Estanzuela, Colonia, Uruguay: CIMMYT-INIA, pp. 33-48.

Rekika D., Zaharieva M., Stankova P., Xu X., Souyris I., Monneveux P. 1998. Abiotic stress tolerance in Aegilops species. In Nachit M. M., Baum M., Porceddu E., Monneveux P. and Picard E. (eds) SEWANA Durum Research Network. ICARDA, Aleppo, Syria, pp. 113-128.

Van Slageren, M.W. (1994): Wild wheats: a monograph of Aegilops L. and Amblyopyrum (Jaub and Spach) Eig (Poaceae). Agricultural University, Wageningen-ICARDA, Aleppo, Syria, 512p.

Zaharieva M., David J., This D, Monneveux P. 1999. Analyse de la diversité génétique d'Aegilops geniculata Roth en Bulgarie. Cahiers Agricultures, 8, 181-188.

Zaharieva M., Monneveux P.,Henry M., Rivoal R., Valkoun J,Nachit M. 2000. Evaluation of a collection of wild wheat relative Aegilops geniculata Roth and identification of potential sources for useful traits. 6th International Wheat Conference, 4-9 June, 2000, Budapest, Hungary.

ZaharievaM., SantoniS., DavidJ. 2001a. Genetic diversity using RFLP of the wild wheat relative Ae. geniculata Roth (Ae.ovata L.) around the Mediterranean basin. Efficiency of molecular markers to build core collection. Genetic Selection Evolution (in press).

Zaharieva M., Gaulin E., Havaux M., Acevedo E., Monneveux P. 2001b. Drought and heat responses in the wild wheat relative Aegilops geniculata Roth: potential interest for wheat improvement. Crop Science (in press)