Abstract only

Nematodes and Root Rots both have a global distribution and can be considered economically important biotic constraints in more marginal wheat production areas of the world, where water and nutrition are not considered optimal. Two key Nematode genera are distributed globally and implicated in significant economic yield loss; the sedentary Cereal Cyst Nematodes (CCN, Hetero- dera spp.) and the migratory endoparasitic Root Lesion Nematodes (RLN, Pratylenchus spp.). Several species ofboth Cyst and Lesion nematode are important including H avenae, H latipons, H filipjevi, H. mani, p thornei and p neglectus. 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 (Nicol et al. , In Press; Nicol, 2002). Root rots globally have been reported to cause between 3- 50% yield loss; RLN between 12-85 and CCN 15- 50% on wheat in various global studies as reviewed by Nicol et al. (In Press) and Nicol (2002). A limited number of published reports exist for these soil borne pathogens from the Central Asian Region. Considering the similarity in W ANA (West Asia and North Africa) in cropping patterns and climate, it is likely that soil borne pathogens in some areas of Central Asia cause important economic losses, in particular under rainfed and limited irrigation conditions. The damage caused by soil borne pathogens may be affected by a number of biotic and abiotic factors and will vary with plant cultivar, soil type, pathogen species and climatic conditions within a geographical area. In general, greater damage potential where plant growth is stressed, i.e. , with poor soil nutrition or structure, temperature or water stress, or where other pathogen pressure occurs. In particular it is well known that a severe and acute phase of root and crown rot occurs under moisture-restricted conditions. Furthermore it is considered with durum wheat that damage and severity of attack by Crown Rot is greater than bread wheat. Although their distribution is worldwide, biotic and abiotic soil borne problems receive much less attention than other types of stresses due to their chronic and endemic nature and to difficulty in working with the soil medium. Unfortunately due to the insidious and persistent nature of these pathogens, the above-ground symptoms are often not readily apparent. It is also not uncommon to find more than one of these root rot pathogens present in the soil at one time, hence forming a soil disease complex, with the host and importantly the environment determining the root disease symptoms observed. Several control methods exist to reduce these pathogens below economic levels of damage such as genetic options (tolerance/resistance), crop rotation, management practices and in some case the use of seed treatments. However, resistance is one of the most effective economic and environmentally friendly control measures to reduce pathogen populations of nematodes below damaging thresholds. Through extensive screening with different programs around the world, several sources of plant resistance have now been identified from alien species, landrace materials and improved cultivars for both Nematodes and Root Rots. The IWWIP (International Winter Wheat Improvement Program), based in Turkey, a collaborative program between TURKEY (Ministry of Agriculture and Rural Affairs), CIMMYT and ICARDA is actively identifying and incorporating sources of Nematode and Root Rot resistance into wheat based on global and regional information. A breeding program exists in CIMMYT headquarters in Mexico for the incorporation of these sources into Spring Wheat (Nicol et al., 2001). The current sources have been documented and used in crossing for Nematodes indicated in Table 1 (Nicol et al., In Press). It is anticipated in the future years that this germplasm will be deployed in regions in the world where these pathogens have been prioritized as productivity constraints. Work within IWWIP (International Winter Wheat Improvement Program) in Turkey is considering the distribution of these pathogens, the yield loss and population dynamics, identification of resistance and subsequent incorporation and these utilization of molecular tools for both pathogen identification and breeding. Limited reports of these diseases are available in Central Asia and we anticipate that the problems in this region are similar to West Asia and North Africa. It is therefore important that similar work occurs in the future -namely to determine the distribution of these pathogens and the yield loss implicated in order to prioritize the breeding needs for the acquisition of directed germplasm. With further understanding of the distribution and importance of both Cereal Nematode and Root Rots, the utilization of these resistant sources should reduce losses caused by these soil borne pathogens.

Global Wheat Program

English

0409|AGRIS 0401|AL-Wheat Program

Juan Carlos Mendieta

INT0599|INT2410

CIMMYT Staff Publications Collection