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Dryland Root Rot: a major threat to winter cereal production under sub-optimal growing conditions

Hakan Hekimhan1, S. Ahmet Bagci2, Julie Nicol3, R. Zafer Arisoy1 and Seyfi Taner1

1 Bahri Dagdas International Agricultural Research Institute, PB 125,42040 Konya, Turkey. hakanhekimhan@hotmail.com
2
Selcuk University, Sarayonu-Konya, Turkey. abagci@selcuk.edu.tr
3
CIMMYT, PK 39, Emek, Ankara, 06511, Turkey. j.nicol@cgiar.org, http://www.cimmyt.org

Abstract

The tolerance of 20 winter cereals, to the dryland root rot complex (Fusarium pseudograminearum, F. culmorum and Bipolaris sorokinana) was investigated for 3 consecutive years through inoculated field trials in Cumra, Turkey. The data clearly indicate significant yield loss is caused by root pathogens with an average across years and varieties of 26%, but also a very high degree of variation between years, with losses of 15, 35 and 27% for the 3 years of the trial. Average and annual % yield losses (yr1, yr2, and yr3) for the different cereal groups were 24 (14, 32, 23) for the 12 bread wheats, 42 (28, 47, 49) for the 5 durum wheats, 12 (0, 31, 3) for the 2 barleys and 18 (17, 14, 23) for the 1 triticale. The degree of intolerance is greatest with durum wheat > bread wheat > triticale > barley. Similarly the Root Rot Severity score for the pathogen complex was found to relate to the level of intolerance. This study clearly demonstrates the importance of conducting yield loss studies over several years and demonstrates that dryland root rot is causing significant yield losses in Turkey. Options for control of these pathogens should be investigated.

Media Summary

Dryland Root Rot is a major concern for winter wheat production systems on the Central Anatolian Plateau of Turkey. A range of tolerance exists within winter cereals to the dryland root complex. There is a need to develop resistant and tolerant germplasm for the dryland root rot complex on cereals.

Key Words

Dryland, Cereal, Root Rot, Yield, Tolerance, Fusarium.

Introduction

Root, crown, or foot root rots are important diseases of cereals worldwide particularly where cereal predominated rotations with sub-optimal growing conditions such as 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.

As root rots occur below the ground and are insidious and persistent, the damage they cause is difficult to assess from year to year due to differences in the location, management and climatic factors. It is well appreciated that the damage cause by this root rotting complex occurs especially under moisture-restricted conditions (Piening et al., 1976; Cook, 1981; Bailey et al., 1989). As reviewed (Mergoum et al., 1995; Nicol, In Press) these dryland root rots have been found in most parts of the world and have been reported to cause yield loss of 3-50%. 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. This is the first study in Turkey to clearly demonstrate the impact of these pathogens on winter cereals grown under marginal conditions of the 5 Million hectares of the Central Anatolian Plateau of Turkey with farm yields averaging 2.2t/ha.

Materials and Methods

Field site and cultivars selected

The field trials were conducted at Cumra, 50 km south-east of Konya over 3 years 2000 to 2003. The continental climate dictates the production of winter cereals and comprises cold winters with freezing temperatures and hot and dry summers. Most rainfall is received throughout the growing season (winter and spring) and averages 250-450mm. Annual rainfall during the 3 years of this experiment were 248, 433 and 390 mm. Due to lack of rainfall in the first year supplementary irrigation was supplied (75mm). Twelve bread wheats (Bezostaya-1, Dağdaş-94, Seri-82, Sultan-95, Kınacı-97, Gerek-79, Gn-91, Odeskaya, Pehlivan, Murat-1, Szen-97 and Kate-A-1),five durum wheats (Selcuklu-97, Kızıltan-91, Altın-98, BDMM98/3-S and Kunduru-1149), 2 six rows barleys (Kıral-97 and Erginel-91) and one Triticale (Tatlıcak-97) were sown in a split-plot, randomized, complete block design with four replications.

Inoculum preparation

The inoculum was cultured on SNA plates for monosporic cultures isolated from Turkey of F. pseudograminearum (F4), F. culmorum (F2) and B. sorokinana (B1) which were mixed in even proportions to make a final conidial concentration of 3 x 105 spores/ml in a water suspension. The seed for the inoculated plots was soaked in a water solution containing the conidia and then left to dry. Confirmation of the inoculation effectiveness is determined during the growing season by collecting selected plants from inoculate and non-inoculated plots and extracting the root rotting pathogens from the root and crown sections.

Parameters recorded during yield trial

Seed of each cultivar was sown at 500 seed/m2 and each plot consisted of eight rows, 6 m long, 20 cm apart. Final harvest area was 6m2 (6 rows x 5 m long). At ripening (Zadock growth stage 91-94), Root Rot Severity (RRS) score was taken based on whitehead formation, the key symptom of Crown Rot from the overall plot. The scoring symptoms used was; 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).

Data analysis

Data for all years were analyzed by using MSTAT-C and SAS analysis program via two factor randomized complete block design with split plot.

Results

From the statistical analysis the individual variables of yield, RRS score and % protein indicated a significant 3-way interaction for cultivar, inoculation and year (P<0.01). Although year variation was great, the overall trend showed very clear differences in bread wheat, durum wheat, triticale and barley (Figure 1). Average and annual % yield losses (yr1, yr2, and yr3) for the different cereal groups triticale were 24 (14, 32, 23) for the 12 bread wheats, 42 (28, 47, 49) for the 5 durum wheats, 12 (0, 31, 3) for the 2 barleys and 18 (17, 14, 23) for the 1 triticale. This clearly demonstrates the degree of intolerance is greatest with durum wheat > bread wheat > triticale > barley.

It is very promising to learn that some of the released Turkish winter wheats such as Dagdas-94 and Sultan-95 have a high level of tolerance to dryland root rot comparable with barley and triticale. The highest yield reduction of 50%, occured with durum wheat candidate cultivar BDMM98/3-S while the lowest, 5%, was observed in barley cultivar Erginel-91 over three years. Some cultivars such as Pehlivan showed little change in yield loss over years, whereas others such as Gerek were highly variable. The variation between the years could be partially explained by climatic differences between years, which is well known to affect disease development and subsequent yield reduction. As with Wildermuth (1986) studies on soil populations of B. sorokiniana reduced rainfall was found to cause a reduced disease incidence. As mentioned the rainfall in the first year was lower than normal and subsequent yield loss over cultivars was 15%, compared with 35% in year 2 and 27% in year 3. Further work is necessary to understand the distribution of rainfall over the season and the impact on yield reductions by dry land root rots as several other studies (Piening et al., 1976; Cook, 1981; Bailey et al., 1989) indicate clearly greater yield reductions occur especially under moisture-restricted conditions.

Figure 1. Mean and range of yield loss% between inoculated and non-inoculated plots from 3 year yield loss trial in Cumra, Turkey 2000-2003. B= Barley; BW= Bread Wheat; DW= Durum Wheat; T= Triticale.

The RRS score based on white head development showed clear significant different over the 3 years of the trial between cultivars (Figure 2). In all cases inoculated plots have a higher RRS score, and in only 4 cases the differences between inoculated and non-inoculated plots were not significant. Reilsolation of root fungi from crown and roots of selected plants in plots with and without inoculum clearly indicating that F. culmorum and Bipolaris sorokinana were the predominant root pathogens in the inoculated plots compared with non-inoculated. This supports the differences the yield losses and RRS score recorded between plots with and without inoculum being related to the pathogens inoculated. Interestingly F. pseudograminearum was inoculated and isolated, but not as often as expected.

There is a general trend as with the % yield loss data for the Root Rot Severity scores to be less with barley < triticale < bread wheat < durum wheat (Figure 2 and 3). Mergoum et al. (1995; 1997) in several studies found similar findings with durum and bread wheat. It is reinforcing to learn that there is no difference in Root Rot Severity between inoculated and non-inoculated plots for triticale and barley, however clear differences are seen for bread and more so for durum wheat (Figure 3). This supports the fact that barley and triticale hold tolerance and offer resistance (reduced symptom development) to these dryland root rots.

Figure 2. Mean Dryland Root Rot Severity (RRS) score between inoculated and non-inoculated plots from 3 year yield loss trial in Cumra, Turkey 2000-2003. B= Barley; BW= Bread Wheat; DW= Durum Wheat; T= Triticale. Indiviudal cultivar*inoculation significant (P<0.001) except for Seri-82, Sultan-95, Kiral-97 and Tatlicak-97.

Figure 3. Mean Dryland Root Rot Severity (RRS) score for cereal groups between inoculated and non-inoculated plots from 3 year yield loss trial in Cumra, Turkey 2000-2003. Highly significant (P<0.0001) differences were found between cereal groups bread wheat vs durum wheat, and bread wheat vs triticale. Within individual cereal groups cultivar*inoculation was significant for only bread and durum wheat (P<0.001).

Conclusion

The paper clearly demonstrates that dryland root rots are causing yield reductions on common winter bread and durum wheats on the Central Anatolian Plateau of Turkey. The inoculation of plots over the 3 years of the trial was a successful tool to demonstrate the yield loss. However, as many other authors in the field have identified obtaining consistent yield loss data over years is very difficult, as seasonal variation is a major factor is the seasonal variation in relation to disease development. This reinforces the necessity to conduct trials over several years with high replication, and to carefully interpret the data.

Within the different cereal groups examined the degree of intolerance is greatest with durum wheat > bread wheat > triticale > barley. Fortunately, some of the released Turkish bread wheats appear to offer a level of tolerance similar to that of triticale and barley. The Root Rot Severity Score was found to be highly correlated with the yield loss for cereal cultivars. Further work is necessary to define the best qualitative symptom scores to measure dryland root rot.

Since it is clear dryland root rots are causing yield loss and breeding materials from this study vary in their tolerance to dryland root rot, a clear and defined screening program to identify sources of tolerance and resistance (reduction in symptoms) has begun with an International focus between the Turkish Minstry of Agriculture and CIMMYT (see poster ‘Strategy for the identification and breeding of resistance to dryland root rot complex for International spring and winter wheat breeding programs’).

References

Bailey KL, Harding H and Knott DR. (1989). Disease progression in wheat lines and cultivars differing in levels of resistance to common root rot. Canadian Journal of Plant Pathology 11, 273-278.

Cook RJ (1981). Fusarium diseases of wheat and other small grain in North America. In ‘Fusarium: Diseases, Biology and Taxonomy’. (Ed. P.E. Nelson, T.A.Toussoun, and R.J. Cook), pp 39-52. (Pennsylvania State University Press, University Park, U.S.A.).

Mergoum M, Lyamani A and Nsarellah N (1995). Root rot of wheat. Al Awamia 89, 1-24.

Mergoum M, Nsarellah N and Nachit M (1997). Evaluation of durum wheat germplasm resistance to root and foot rot disease complex (Fusarium culmorum and Cochliobolus sativus) in Morocco. Plant Genetic Resources Newsletter 109, 11-14.

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

Piening LJ, Atkinson TG, Horricks JS, Ledingham RJ, Mills JT and Tinline RD (1976). Barley losses due to common root rot in the prairie provinces of Canada, 1970-1972. Canadian Plant Disease Survey 56, 41-45.

Wildermuth GB (1986) Geographic distribution of common root rot and Bipolaris sorokiniana in Queensland wheat soils. Australian Journal Experimental Agriculture 26, 601-606.

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