Figures (2)  Tables (3)

    • Figure 1. 

      Maize plots in farmer's fields located at very high altitude environments (> 3,000 masl). Usually, the crop is fertilized with goat manure and irrigated by furrow throughout the growing season following weekly turns organized by the community. Weeds are manually controlled, and pest incidence is overall very low. Sowing is done manually leading to significant stand heterogeneity (a), and furrows are placed against the slope when appropriate (a, left). (b) Intercropping is also a usual practice. Geographical coordinates, altitude and date are indicated in the right corner of each image.

    • Figure 2. 

      Relative change for different factors or crop parameters measured at 3300 masl compared with 2300 masl during experiments carried out at two high altitude sites of Argentina: Hornillos (2,300 masl, Jujuy) and El Rosal (3,300 masl, Salta) during 2021−22 (calculated from absolute values in Salve et al.[9]).

    • TraitLocationLatitudeAltitudinal rangeResponse to
      increased altitude      		References
      Phenology and canopy development
      Days to tasselingEast-African countries8°−(−13)°352 vs 1913Increase (+27 d)Darrah and Penny[37]
      Days to tasselingEast-African countries8°−(−13)°1210 vs 1913Increase (+27 d)Darrah[80]
      Crop cycle lengthKenya0−1°1268 vs 2250Increase (80 d)Cooper[13]
      Crop cycle lengthMexico19°600 vs 2050Increase (69 d)Pace[27]
      Crop cycle lengthMexico19−21°60 vs 2650Increase (58 d)Jiang et al.[8]
      Thermal timeKenya0−1°1268 vs 2250UnchangedCooper[13]
      Thermal timeMexico19−21°60 vs 2650DecreaseJiang et al.[8]
      Final leaf numberKenya0−1°1268 vs 2250Decrease (-2 leaves)Cooper[13]
      Final leaf numberMexico19−21°800 vs 2240DecreaseLafitte & Edmeades[14]
      Final leaf numberMexico19−21°60 vs 2650Increase (2,4 leaves)Jiang et al.[8]
      Leaf sizeKenya0−1°1268 vs 2250Increase, then decreaseCooper[13]
      Leaf sizeMexico19−21°800 vs 2240Increase, then decreaseLafitte & Edmeades[14]
      Canopy senescenceMexico19−21°800 vs 2240DelayedLafitte & Edmeades[14]
      Canopy senescenceSouthafrica(−29)°420 vs 1620AcceleratedWilson et al.[35]
      Biomass and yield
      BiomassSouthafrica(−29)°420 vs 1620UnchangedWilson et al.[35]
      BiomassMexico19−21°800 vs 2240SimilarLafitte & Edmeades[14]
      BiomassMexico19−21°60 vs 2240Increase (+ 147%)Jiang et al.[8]
      YieldKenya0°1525 vs 2593UnchangedArkel[81]
      YieldEast-African countries8°−(−13)°352 vs 1913Increase (+ 60%)Darrah & Penny[37]
      YieldEast-African countries8°−(−13)°1210 vs 1913Increase (+ 18%) Darrah[80]
      YieldKenya0−1°1268 vs 2250Increase (+ 82%)Cooper[13]
      YieldMexico16°1500 vs 2150Increase (+ 300%)Mercer et al.[38]
      YieldMexico19−21°60 vs 2240Increase (+ 155%)Jiang et al.[8]
      YieldMexico19°1850 vs 2400Increase (+ 800%)Pace[27]
      ProlificyKenya0−1°1268 vs 2250Increase (+ 58%)Cooper[13]
      Grain numberMexico19°1850 vs 2400Increase (+ 83%)Pace[27]
      Grain numberSouthafrica(−29)°420 vs 1620UnchangedWilson et al.[35]
      Grain numberKenya0−1°1268 vs 2250Increase (+ 48%)Cooper[13]
      1000 grain weight (primary cob)Kenya0−1°1268 vs 2250Increase (+ 25%)Cooper[13]
      1000 grain weightMexico19°1850 vs 2400Increase (+ 64%)Pace[27]
      1000 grain weightMexico19−21°60 vs 2240Increase (+ 9%)Jiang et al.[13]
      1000 grain weightMexico19°600 vs 2050Increase (400%)Pace[27]

      Table 1. 

      Changes in different traits in response to increasing altitude based on available literature. When more than one season was available, average change across seasons is considered; when several adaptation groups were tested, the response of the highland-adapted group is reported (or the best-performing genotype). Relative values for the responses are approximate as most of the results are based on figures.

    • GroupRepresentative racesCycle lengthPlant sizeEar traitsEndospermUses
      'Capias''Capia' ('blanco'/ 'variegado'/ 'rosado'/ 'amarillo'/ 'marrón'), 'Cuzco', 'Chulpi' and 'Culli'LongTall plantsBig ears, 16−20 number of rows, large kernels, wide variety of coloursFloury (dextrinous
      in the Chulpi race)      		Typical food and drinks: 'Capias', 'Mote', 'Tamal', 'Tijtincha', Äpi'and 'Chicha morada'
      'Cristalinos''Morocho', 'Calchachí', 'Cristalino Blanco', 'Cristalino Amarillo' (or 'chico'), and 'Amarillo de Ocho' (or 'grande').MediumMedium plantsCrystalline endosperm, yellow or white colorCrystalline (flint)Typical food: 'Locro', 'Mazamorra', 'Humita' and 'Chicha'
      'Reventadores''Pisingallo', 'Perlita'ShortMedium plantsSmall kernels, pointed shape, poppedCrystalline (flint)Pop-corn and typical food and drinks ('chilcan',
      'ulpada' and 'miskopitapi').
      'Altiplano''Bola blanca' and 'altiplano'ShortSmall plantsSmall and round ears with small kernels. Irregular kernel row arrangementFloury or crystallineGrain or forrage

      Table 2. 

      Characterization of main maize races cropped in high altitude environments from the Northwest of Argentina based on races defined by Cámara Hernández et al.[47]. The criteria we followed for grouping races was based on the different traits indicated in columns.

    • GROUPLand tenureWater originWater accessSoil textureSoil erosionMaize purposeFertilizerYears using seedRaces sown anuallyEarliest sowingEarliest harvest
      2,100-2,400 masl
      (n = 14; avg = 2.2 has)
      2,500-3,900 masl
      (n = 9; avg = 1 ha)
      Color references
      OwnerRiver/ ditchEnoughSandySevereBothManure (own)< 10 years1 or 2Before OctoberBefore April
      CommunityThawNot enoughClayModerateSelf-consumptionManure (bought)between 10 and 203 or 4OctoberApril
      BothNo answerSiltyNo erossionSellingBoth/ others> = 20 years> 4After OctoberAfter April

      Table 3. 

      Own results obtained from surveys to farmers carried out in 2021 as part of a FAO Project (detailed in the text). A total of 23 farmers were interviewed across an altitudinal gradient spanning from 2,100 to 3,900 masl; results were grouped into two groups according to altitude.