Megaenvironments

CIMMYT develops improved wheat germplasm for use in developing and emerging countries, which grow wheat on about 110 m ha (Lantican et al., 2005). To address the needs of these diverse wheat growing areas, CIMMYT uses the concept of mega-environments (ME) (Rajaram et al., 1994) to target germplasm development. A ME is defined as a broad, not necessarily contiguous area, occurring in more than one country and frequently transcontinental, defined by similar biotic and abiotic stresses, cropping system requirements, consumer preferences, and, for convenience, by a volume of production. The ME to which wheat breeding stations participating in IWIN are assigned to is given in Figure 1 (Hodson and White, 2007a).

Agroclimatological parameters defining Wheat Mega-environments

    SPRING WHEAT FACULTATIVE WHEAT WINTER WHEAT
    Temperature
    16°C > Tmin* > 11°C 16°C > Tmin* ≥ 3°C 11°C > Tmin* ≥ 3°C -13°C > Tmin* 3°C > Tmin* ≥ -2°C -2°C > Tmin* ≥ -13°C
Rainfall Irrigated¹         7 10
Low/Irrigated¹     1      
Low   4C 4A, 4B   9 12
Moderate/Low       6B    
High/Irrigated¹ 5       8 11
High   2A, 2B, 3   6A    

* average min for the coolest quarter (3 consecutive coolest months)
¹ >5% of 5 arc min grid cell equipped for irrigation

NOTES:

  • ME2A Tmin judged in wettest quarter (3 consecutive wettest months) with = 250mm precipitaion, elevation = 1400m
  • ME2B coolest quarter precipitation = 150mm, elevation <1400m
  • ME3 identical to ME2 (merged A&B) except soil pH < 5.2
  • ME4 wettest quarter precipitation = 100mm, < 400mm
  • ME6 only at high lattitudes (> 45° N or S)
  • ME6 also has a Tmin = 9°C for warmest quarter
  • Recently suggested that ME8/9 be given a higher temperature range (6°C > Tmin* = 1°C) to include southern US sites
  • Recently suggested that ME11/12 be given a higher temperature range (1°C > Tmin* = -13°C) to include W.Europe Sites


 

Spring Wheat

ME1
Autumn sown (spring-sown rare), largely white/amber grain
Low rainfall, irrigated (>5% of 5 arc min grid cell equipped for irrigation)
Average min. temperature for coolest quarter 11°C > T = 3°C
Major constraints: leaf rust, stem rust, stripe rust, lodging
Representative sites: Gangetic Valley, India; Indus Valley, Pakistan; Nile Valley, Egypt; Yaqui Valley, Mexico

ME2A
Spring sown, largely red grain (except Ethiopia)
Highland summer rain (elev. = 1400m), wettest quarter precipitation = 250mm
Average min. temperature for wettest quarter 16°C > T = 3°C
Major constraints: barley yellow dwarf virus, stripe rust, head scab, septoria, tan spot
Representative sites: Kulumsa, Ethiopia; Toluca, Mexico

ME2B
Autumn sown, largely red grain
Lowland winter rain (elev. < 1400m), coolest quarter precipitation = 150mm
Average min. temperature for coolest quarter 16°C > T = 3°C
Major constraints: barley yellow dwarf virus, stripe rust, head scab, septoria, tan spot
Representative sites: Izmir, Turkey; Pergamino, Argentina

ME3
SAME AS GENERAL ME2 (A and B merged)—main difference soil pH < 5.2
Largely red grain (except Himalayas)
Additional constraints: acid soil (Aluminum, Manganese toxicity)
Representative sites: Passo Fundo, Brazil; Mpika, Zambia

ME4A
Autumn sown, largely white grain
Mediterranean climate, post-flowering moisture deficits, late season frosts
Low rainfall, wettest quarter precipitation = 100mm, < 400mm
Average min. temperature for coolest quarter 11°C > T = 3°C
Major constraints: drought, heat, rust, common bunt, septoria, tan spot, root diseases
Representative sites: Aleppo, Syria; Settat, Morocco

ME4B
Autumn sown, largely red grain
Winter drought or Southern Cone-type rainfall, pre-flowering moisture deficits
Low rainfall, wettest quarter precipitation = 100mm, < 400mm
Average min. temperature for coolest quarter 11°C > T = 3°C
Major constraints: drought, rust, common bunt, septoria, fusarium, tan spot, root diseases
Representative sites: Marcos Juárez, Argentina

ME4C
Autumn sown (after monsoons), only white grain
Receding moisture levels after sowing
Low rainfall, wettest quarter precipitation = 100mm, < 400mm
Average min. temperature for coolest quarter 16°C > T = 3°C
Major constraints: drought, rust, common bunt, septoria, tan spot, root diseases
Representative sites: Dharwar, India

ME5
Autumn sown
Tropical high rainfall, and/or irrigated (>5% of 5 arc min grid cell equipped for irrigation)
Average min. temperature for coolest quarter 16°C > T > 11°C
Major constraints: heat, spot blotch, leaf & stem rust
Subdivided into high humidity areas (Joydebpur, Bangladesh; Paraguay), and low humidity areas (Kano, Nigeria; Wad Medani Sudan)

ME6
Spring sown, high latitude (>45° N or S) – photosensitive varieties
Average min. temperature for coolest quarter T < -13°C
Average min. temperature for warmest quarter T = 9°C
Major constraints: rust, root diseases, tan spot
Subdivided into ‘A’, high rainfall areas (Harbin, Heilongjiang, China) and ‘B’, semi-arid areas (Astana, Kazakhstan)

  

Facultative Wheat

ME7
Autumn sown
Irrigated
Average min. temperature for coolest quarter 3°C > T = -2°C
Major constraints: cold, stripe rust, mildew
Representative Sites: Zhenzhou, Henan, China
Note: Sites currently listed as ME7 sometimes do not meet this criteria, although almost all these sites fit the ME10 criteria (perhaps ME7 isn’t distinct yet)

ME8
Autumn sown
High rainfall/irrigated, annual precipitation = 500mm
Average min. temperature for coolest quarter 6°C > T = 1°C
Major constraints: cold, stripe rust, mildew, septoria, root rots
Representative Sites: Temuco, Chile; Corvallis, Oregon, USA
Note: Perhaps annual precipitation = 800mm for USA to have distinct ME8/9 sites

ME9
Autumn sown
Low rainfall, annual precipitation < 500mm
Average min. temperature for coolest quarter 3°C > T = -2°C
Major constraints: cold, drought, stripe rust, root rots
Representative Sites: Diyarbakir, Turkey; Vernon, Texas, USA
Note: Perhaps annual precipitation < 800mm for USA to have distinct ME8/9 sites



Winter Wheat

ME10
Autumn sown
Irrigated
Average min. temperature for coolest quarter -2°C > T = -13°C
Major constraints: winter kill, rust, mildew
Representative Sites: Beijing, China

ME11
Autumn sown
High rainfall/irrigated, annual precipitation = 500mm
Average min. temperature for coolest quarter 1°C > T = -13°C
Major constraints: winter kill, rust, septoria, mildew
Representative Sites: Cambridge, UK; Krasnodar, Russia
Note: Perhaps annual precipitation = 800mm for USA to have distinct ME11/12 sites

ME12
Autumn sown
Low rainfall, annual precipitation < 500mm
Average min. temperature for coolest quarter 1°C > T = -13°C
Major constraints: winter kill, drought, stripe rust, bunts, root rots
Representative Sites: Ft. Collins, Colorado; Manhattan, Kansas, USA
Note: Perhaps annual precipitation < 800mm for USA to have distinct ME11/12 sites