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Strategy for the identification and breeding of resistance to dryland root rot complex for International spring and winter wheat breeding programs.

Julie Nicol1, S. Ahmet Bagci2, Hakan Hekimhan3, Berna Tunali4, Necmettin Bolat3, Hans Joachim Braun1 and Richard Trethowan1

1 CIMMYT International (International Wheat and Maize Improvement Center), PK 39 Emek, Ankara, 06511, Turkey.
Email jnicol@cgiar.org, www.cimmyt.org
2
Selcuk University, Sarayonu, Konya, Turkey, bagcia@hotmail.com
3
MARA (Turkish Ministry of Agriculture and Rural Affairs), BDIARI (Bahri Dağdaş International Agricultural Research
Institute), Eregli Yolu 7. km,P.K 125, Karatay, Konya, Turkey. hakanhekimhan@hotmail.com
4
PPI (Plant Protection Central Research Institute), Bagdat Street, Number.250, Yenimahalle, Ankara, Turkey.
bernatunali@hotmail.com

Abstract

Root, crown and foot root rots, including the complex of Crown Rot Fusarium (F. psuedogramiearum, F. culmorum) and Common Root Rot (Bipolaris sorokinana) are causing economic yield loss in many parts of the world where cereals predominate the cropping system and sub-optimal growing conditions and rainfed or limited irrigation practices are common. CIMMYT in collaboration with the Turkish Ministry of Agriculture and Rural Affairs have established an International field and laboratory screening program for identifying spring and winter wheat accessions with resistance to these root pathogens. Assessment of tolerance with the most promising lines is also occurring to identify accessions with combined resistance and tolerance. The strategy in place is described with reference to subsequent breeding and seed dissemination in addition to some of the most promising lines identified.

Media Summary

The strategy used to identify and develop new sources winter and spring wheat with resistance to the dryland root rot complex (Fusarium pseudograminearum, F. culmorum and Bipolaris sorokinana) for International Spring and Winter Wheat nurseries .

Key Words

Wheat, root rot, resistance, dryland, breeding, tolerance.

Introduction

Root, crown, or foot root rots are one of the important diseases of cereals worldwide where cereal predominated rotations, sub-optimal growing conditions and rainfed or limited irrigation practices are common. Dryland Root Rots generally include a complex of species such as Common Root Rot (Bipolaris sorokiniana (syns. Helminthosporium sativum, H. sorokinianum, Teleomorph Cochliobolus sativus (Ito &Kurib.) Dresch.ex Dast.)), and several species of Crown Root (Fusarium spp.). The two most reported Fusarium species are F. pseudograminearum (formerly F. graminearum Group 1, Teleomorph Gibberella coronicola) and F. culmorum, while several others such as F. acuminatum, F. avenaceum and F. crookwellense have also been reported.

Yield loss caused by these Cereal Root Pathogens has been documented in many regions of the world including Europe, America and in particular the more marginal cereal production areas of West Asia, North Africa, Australia and Canada and are reported between 3-50% (Diehl et al., 1983; Tinline et al., 1988; Wildermuth et al., 1992; Nicol et al. 2001; Hekimham et al., 2004; Nicol, In Press). Considering the similarity in WANA (West Asia and North Africa), parts of South America, South Africa and other parts of the world in relation to cropping patterns and climate, it is likely that soil borne pathogens cause important economic losses on wheat, in particular under rainfed and limited irrigation conditions around the world.

In less developed countries biotic and abiotic soil-borne problems receive much less attention than other types of stresses due to their chronic and endemic nature, and difficulty in working with the soil medium. Resistance, which is defined as a reduction in the multiplication of the pathogen, is one of the best methods to control these diseases. Currently there are no known effective sources of resistance against dryland root rot pathogens available in commercially grown wheat varieties. Furthermore the current sources of resistance are generally in unadapted germplasm that will require considerable breeding investment to produce an adapted variety. Hence a precise laboratory/field breeding strategy has been developed to identify and incorporate new sources of resistance, particularly those identified from highly adapted backgrounds.

CIMMYT has been working on the identification and subsequent incorporation of resistance to these soil borne pathogens in spring wheat backgrounds since 1999 in Mexico. In Turkey, the International Winter Wheat Improvement Program (IWWIP), a collaboration between TURKEY (Ministry of Agriculture and Rural Affairs), CIMMYT and ICARDA (International Center for Research in Dryland Agriculture) have identified this problem as a priority for winter wheat. As a result a National project conducted with Turkish and CIMMYT scientists was initiated since 1999, and as result a clear strategy is now in place for screening both winter and spring wheat for root rot resistance and the subsequent incorporation into breeding material and dissemination of International Nurseries. The strategy used for this and some of the major findings to date will be discussed.

Methods

International linkages

As this work is developing international wheat germplasm for both winter and spring wheats a clear strategy for screening, validation and dissemination has been developed between CIMMYT Mexico and the IWWIP program in Turkey. Spring wheats are developed in Mexico at CIMMYT headquarters and the complimentary winter wheats in Turkey under the IWWIP program and these materials undergo validation in Turkey in the field location of Cumra, near Konya. Results of the validation are used for both Spring and Winter wheat programs to further develop and disseminate germplasm.

Screening nurseries

As illustrated in Figure 1 the sequence of germplasm screening, validation and subsequent incorporation into both spring and winter wheat breeding programs is presented. Germplasm entering these nurseries is sourced from several breeding programs around the world including CIMMYT, IWWIP, Turkish national materials and a number of ARIs and National Programs. In all cases the observation plots (RRPN, RREL and RRCN) are inoculated under field conditions in 1.5m pairwise plots, one with inoculum and the other without. The inoculum is cultured on SNA plates from monosporic cultures isolated from Turkey of F. pseudograminearum (F4), F. culmorum (F2) and B. sorokinana (B1) which are either mixed (RRPN, RREL) or kept separate (RRCN) at a concentration of 3 x 105 spores/ml to the seed before planting. The seed are soaked in a water solution containing the conidia and then left to dry. Around 15g of seed are used for each observation row and the total volume of water absorbed by the seed is 6ml, making total inoculation concentration around 1.8 x 105 spores/g seed. The yield trial seed are similarly inoculated. Confirmation of the inoculation effectiveness is determined during the growing season by collected selected plants from inoculate and non-inoculated plots and extracting the root rotting pathogens from the root and crown sections.

Scoring root disease resistance reaction

The plants are scored twice, comparing with and without inoculation plots, side by side for the symptom development of these root pathogens. After heading on two occasions at ripening (Zadock growth stage 91-94) and at full maturity (Zadocks growth stage 99), each plot was given a score from 0-5. The first score is based on whitehead formation (premature death of tillers), which is the key symptom of Crown Rot; 0 (no symptoms), 1 (<5% white heads), 2 (>5-10% white heads), 3 (10-30% white heads), 4 (30-50% white heads) and 5 (> 50% white heads). The second score is when the plant is fully mature and considers the overall plant stand and the growth reduction (gr) between inoculated vs control; 0 (equal growth), 1 (<5% gr), 2 (>5-10% gr), 3 (10-30% gr), 4 (30-50% gr) and 5 (> 50% gr). These two scores are used to rank the material for subsequent promotion.

The elite germplasm (RRAL) are then screened in the greenhouse for their resistance reaction under individual inoculum pressure using a similar seed inoculation technique under controlled conditions at 20-250C with 7 replicates in small tubes for 9 weeks with the Crown and Root Scores collected on the basis of lesioning (data not presented here). Similarly tolerance (yield loss) is also assessed in yield plots in Cumra, as ideally germplasm which pertains resistance and tolerance should have higher priority for breeding than resistance alone.

Results

To date this strategy for screening for root disease resistance for both spring and winter wheat has identified new sources of resistance, validated known sources and confirmed resistance in advanced lines specifically developed for root rot resistance. Since 1999, over 5000 lines have been screened and to date 571 lines have been promoted to various nurseries.

Figure 1. International screening program for cereal root rots resistance/tolerance (Fp = Fusarium pseudograminearum, Fc = F. culmorum, Bs = Bipolaris sorokiniana)

A summary of some of the most promising lines is presented in Figure 2 where it can be clearly seen that there are a number of winter and spring wheats which are providing a high level of resistance better than the known check varieties (Sunco and 2-49). Major progress has been made with the spring wheat material, where a number of crosses (Sunco/Pastor) are not only providing a higher level of resistance, but also yield upto 20% higher than either of the parents. Furthermore materials have been specifically breed to develop multiple disease resistances, such as GS50AT34/Sunco which combines Crown Rot with Root Lesion Nematode.

Some of the preliminary yield data from the winter wheats indicates some of the materials with a high level of resistance, for example the released Turkish variety Dagdas 94, also have a high level of tolerance, which is equivalent to the more tolerant triticale, Tatlicak 97 and barley, Erginel 91. However another widely grown variety Gerek 79, offers some resistance, but unfortunately no tolerance.

Conclusion

Major progress is being made for both International spring and winter wheat breeding programs as a result of the clear and strong integration of CIMMYT and Turkey scientists working on a clearly defined strategy for the identification and subsequent incorporation of resistance to these dryland root rotting fungi. Refinement of the strategy is continually occurring.

Figure 2. Summary the Root Rot Severity Scores comparing inoculated and non-inoculated plots from the Root Root Elite Line (RREL) Nursery 0203 with 3 replicates in Cumra Turkey. SW:Spring Wheat, WW: Winter Wheat and DW- Durum Wheat. SED = 0.5

Since the beginning of this work, over 500 spring wheat and 200 winter wheat targeted crosses have been made and now a number of advanced high yielding lines and released cultivars are being confirmed to release to international breeding programs around the world. In 2003 over 14 international dryland root rot disease resistant nurseries were prepared for over 14 countries, including our NARs partners in developing countries and a number of advanced research institutions. Both CIMMYT and Turkey believe this work will have major benefits to farmers in dryland regions of the world where these root rots are present, but we also implicate the use of integrated approaches of control such as crop rotation.

References

Diehl JA, Tinline RD and Kochhann RA (1983). Perdas em trigo causadas pela podridao comum de raizes no Rio Grande do Sul, 1979-1981. Fitopatologia Brasellia 8, 507-511.

Hekimhan H, Bagci A, Nicol J, Arisoy Z, Taner S and Sahin S (2004). Dryland Root Rot : a major threat to winter cereal production under sub-optimal growing conditions. Poster paper presented at “New directions for a diverse planet”. Proceeding of the 4th International Crop Science Congress, 26 Sep – 1 Oct 2004, Brisbane, Australia. www.regional.org.au/au/cs

Nicol J.M. (In Press). Root Rots, In: Durum Wheat Breeding: Current Approaches and Future Strategies’, Food Product Press (New York, USA), The Haworth Press Inc.

Nicol JM, Rivoal R, Trethowan RM, van Ginkel M, Mergoum M and Singh RP (2001). CIMMYT’s approach to identify and use resistance to nematodes and soil-borne fungi, in developing superior wheat germplasm. In: ‘Wheat in a Global Environment’. (Ed. Z.Bedo and L. Lang) Proceedings of the 6th International Wheat Conference, 5-9th June 2000, Budapest, Hungary. Kluwer Academic Publishers, Netherlands, pp. 381-389.

Tinline RD, Wildermuth GB and Spurr DT (1988). Inoculum Density of Cochliobolus sativus in Soil and Common Root Rot of Wheat Cultivars in Queensland. Australian Journal Agricultural Research 39, 569-577.

Wildermuth GB, Tinline RD and McNamara RB (1992). Assessment of Yield Loss Caused by Common Root Rot in Wheat Cultivars in Queensland. Australian Journal Agricultural Research 43, 43-58.

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