Chapter 6-7: Abiotic and Biotic Stress - FAO

• How to identify and characterize key environmental factors affecting crop genetic diversity and productivity

• How to collect and analyse information on farmers’ knowledge of their biophysical environments

• The potential role of crop genetic diversity in supporting ecosystem functions.

Chapter 6: Abiotic and Biotic Environment

Abiotic and biotic factors vary

• Over time (with seasonal, annual, and stochastic changes) and

• In space, from micro-environmental to eco-regional scales

Geographical

• topography,

• altitude,

• slope,

• aspect

Climatic Factors

• Temperature: fluctuations and extremes

• Water: amount and distribution of rainfall

• Light: light intensity

• Wind: wind velocity

• Air: levels of CO2 concentration

Soils• texture, fertility, toxicity, moisture

North Carolina State University

Environmental Disturbance and Climate Change

Carbon Dioxide Levels and Climate Change

Biotic Components of Agricultural Ecosystems• Pathogens

• Pests

• Biological Control Agents

• Weeds

• Soil Organisms

• Pollinators

Functional group Influence

Earthworms --soil porosity and soil nutrient relations through channeling, and

ingestion of mineral and/or organic matter

Termites and ants --soil porosity and texture through tunneling, soil ingestion and transport,

and gallery construction

--nutrient cycles through transport, shredding, and digestion of organic

matter

Other macrofauna

such as woodlice,

millipedes, insect

larvae

--act as litter transformers, with an important shredding action on dead

plant tissue and their predators (centipedes, larger arachnids, some other

types of insect)

Nematodes --turn over soil in their roles as root grazers, fungivores, bacterivores,

omnivores, and predators

--occupy existing small pore spaces in which they are dependent on

water films

--usually have very high generic and species richness

Mycorrhizae --associate with plant roots, improving nutrient availability and reducing

attacks by plant pathogens.

--different varieties of a crop can respond differently to inovulation with

mycorrhizae (wheat) and colonization by mycorrhize is dependent on

host genotype (pearl millet)

Rhizobia --N-fixing microsymbionts, which transform N2 into forms available for

plant growth

Microbial biomass --an indirect measure of the total decomposition and nutrient recycling

community of a soil. Microbial biomass is contributed by three very

diverse taxa: fungi, protists, and bacteria (including archaea and

actinomycetes); however it is not usually practical to separate these

during measurements.

Sources: Swift and Bignell (2001); Moreira et al. (2008).

Key functional groups of soil organisms

Farmer characterization of their abiotic and biotic environment

Farmers’ ecological knowledge is systematic

• Farmers possess detailed folk taxonomies for identifying and classifying the abiotic and biotic components of the environment.

• Based on their experiences and perceptions, farmers characterize and develop classification systems or ethno-taxonomies for plants, animals, soils, weather phenomena, vegetation types, landforms, for stages of ecological succession, pests and diseases, weeds, plant competitors, mutualists, and other ecological domains

A suggested list of environmental domains and their dimensions to discuss with farmers.

Domain Dimensions to discuss with farmers

Landform Elevation, location and shape, includes hill tops, rivers, valley

bottoms, plateaux, cliffs

Soil Color, texture, fertility, acid-alkalinity, workability, humidity,

consistency, drainage profile, utility, salinity, living matter in the soil,

susceptibility to soil erosion, leaching

Climate Temperature, rainfall, evapotranspiration, elevation, exposure,

topography (including position of land masses and bodies of water)

wind, seasonality

Surrounding

vegetation

type

Floristic composition (including dominant species), extent of human

management/ disturbance, indicator species of the surrounding

vegetation, weeds

Land-use

zone

Technology applied, extent of management, distance to household,

ownership

Stage of

ecological

succession

Shifting cultivation importance, number of fallow years, extent of

original disturbance

Farmers' soil classification and maize diversity conservation in Yucatán, Mexico

Soil† Ts

ek

’el

Bo

x-l

u’u

m

Pu

s-l

u’u

m

Ek

-lu

’um

Ch

ac

-lu

’um

Ka

nk

ab

Ya

’ax

om

Ak

’alc

he

Litosol √ Rendzine √ √ √ √ Cambisol √ √ √ Luvisol √ √ √ √ Nitosol √ Vertisol √ √

Gleysol √

This detailed soil classification system is an important aspect of landrace

cultivation in Yaxcabá village, Yucatán, Mexico, where farmers plant different

maize varieties to land area with specific soil and topography types, based on

the varieties' time to maturity. Long-season maize is planted to higher, rockier

soil, while early maturing varieties are planted to level areas of red, organic

soils, such as in home gardens (Arias et al. 2000).

FAO

Defining healthy and non healthy plants

Healthy Not healthy Disease Pest

Healthy Not healthy

The descriptions of unhealthy plants

13 descriptors

• Green leaf

• Growing well

• Plump seed

• High yield

• Large spike

• More tillering

12 descriptors

• Spot on leaf

• Leaf wither

• Insect hole

• Dwarf plant

• Smaller grain

Farmer descriptions of healthy plants Barley, China; Guo et al. 2011)

Identification pest and diseases and their effect on the crop

Pest/disease description

Plant part affected

Stage affected

Descriptive

traitsStagePlant partPest/

Diseases

pestes/

enfermedades Description hojas tallos raices vaina

grano o

semilla

Flora-

cion vaina 2o desh

lancha X x

frutos manchados

(vainas) X x

plantas sin hojas X X X x

pudrición o lancha x x

planta sin hojas y

frutos manchados X X x

otras enfermedades

que Vd no conoce X x

Etapa del cultivoParte afectada Growth stagePlant part affected

Farmers’ descriptions of pests/diseases

Pest/disease

Descriptions

rust

smut

aphid

cutworm

yellow dwarf

(Shangri-la)

Weevil

(Songming)

the leaves withered, rust on the leaves and

stems, dwarf, small spikes, small grains, low

yields

the spikes became black, no grain

sucked the juice, yellow leaves and stems, slow

growth, shriveled grains

broken roots, plants died

dwarf, yellow leaves, low tillers, low yields

insect holes in the grains

Barley, Yunnan, China – Guo et al. 2011)

Parts and stages damaged by pest/disease

Pest/disease

Damage positions Damage stages

leaf stem spike root grain seeding tiller heading maturity grain

rust

smut

aphid

cutworm

yellow dwarf

weevil

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

pest/dis

ease

types of damageOverall

importance of

pest/disease

yiel

d

grain

size

fee

d

heig

ht

rust 3 4 3 3 3

smut 4 1 4 4 4

aphid 1 2.5 2 2 2

cutwor

m5 5 5 5 5

yellow

dwarf2 2.5 1 1 1

Farmers’ beliefs on origin of pests and diseases

23 reasons

• Drought

• Rain

• Soil

• Pest

• Tree, grass and ditch

• Neighboring fields

• Air

• Most farmers considered:

• Dry year –

• Wet year +

• Hot year –

• Cold year +

Majority of the farmers believed that the barley in a wet,

cold year had higher resistances than in a dry, hot year

Songming, Yunnan, China, (Guo et al., 2011)

Temperate Central Asia and Tropical SE Asia Fruit Tree Diversity:

A shared hypothesis:

“Variety diversity of fruit trees increases levels of pollination service and increases productivity”

Apple pollination Mango pollination

Environmental factor Possible farmer response to alter environment

Extreme cold Crop sheltering, frost coverage

Extreme heat Crop shading

High clay content/poor drainage Removal of hardpans, addition of drainage lines

High sand content/rapid drainage Addition of water retention lines

High gravel/rock content Removal or rock material

High or low pH Fertilizers, soil additives

Low nutrient content Fertilizers, soil additives, intercropping, crop

rotation with legumes

High aluminum or salt content Fertilizers, soil additives

High precipitation/waterlogged

soils

Addition of drainage lines

Low annual precipitation Irrigation systems/ water harvesting

Low seasonal precipitation Temporary/seasonal irrigation systems

Desertification Sand barriers

High erosion potential Flattening field slopes, developing terraces

Low light intensity Thinning possible shade

Long/short photoperiod Agroforestry, crop rotation

Strong local winds Plant/build windbreaks, agroforestry

Pests Pesticides, physical barriers, intercropping, crop

rotation

Diseases Avoidance of conditions favorable to disease,

fungicides, crop rotation

Plant competition Weeding, reduced plant spacing, herbicides

Environmental stresses and possible agronomic management responses by farmer

Crop genetic diversity

(intra-specific diversity)

continuous biomass

ensured

Different

resource

acquisition

efficiency

Increased facilitative

interactions

Increase in number of

functional traits

Production system more

resistant and resilient to

disturbance

Specific

resistance to

pests and

diseases

Diversity of

pollinators

supported

Reduced

movement of

pest and

disease

Genotype

complement

-arity

Increased N-

Fixation

Improved soil

processes

Improved soil

processes (soil

formation; N-

fixation; organic

matter)

CO2

sequestration

Longer

period of

food for

pollinators

Decompo

sition and

nutrient

cycling

Pest and

disease

control

More

efficient

pollination

longer period

for CO2

sequestration

Reduced

soil erosion

more efficient

CO2

sequestration

Improved ecosystem functions

Differing

architecture

reduces stress to

other genotypes

Pollinator

sharing

attraction

Longer

period of

vegetation

coverage


More diversity in

specific resistance

to pests and

diseases

Increase in number

of functional traits

continuous

biomass ensured

Production system

more resistant and

resilient to

disturbance


interactions

Pest and disease regulation

Different

resource

acquisition

efficiency

Genotype

complement

-arity

Differing

architecture

reduces stress to

other genotypes

The mixture effect

+ reduced

movement of pest

and pathogens

Intra-specific crop diversity – pest and disease regulation


Longer period of

food for pollinators

Diversity of

pollinators

supported

Increase in number


continuous

biomass ensured

Production system

more resistant and

resilient to

disturbance


interactions

More efficient pollination

Different

resource

acquisition

efficiency

Genotype

complement

-arity

Differing

architecture

reduces stress to

other genotypes

Pollinator sharing

attraction

Cost effectiveness?: Increasing crop genetic diversity versus increasing landscape heterogeneity

Intra-specific crop diversity (Pollination)


Longer period of

vegetation

coverage

Increased N-

Fixation

Improved soil

processes

Reduced soil

erosion

Increase in number


continuous

biomass ensured

Production system

more resistant and

resilient to

disturbance


interactions

Improved soil processes

(soil formation; N-

fixation; organic matter)

Different

resource

acquisition

efficiency

Genotype

complement

-arity

Differing

architecture

reduces stress to

other genotypes

Decomposition

and nutrient

cycling

Intra-specific crop diversity – soil and nutrient processes

Intra-specific crop diversity – CO2 sequestration


longer period for

CO2 sequestration

more efficient

CO2

sequestration

CO2

sequestration

Increase in number


continuous

biomass ensured

Production system

more resistant and

resilient to

disturbance


interactions

Jarvis et al., in preparation

Chapter 6-7: Abiotic and Biotic Stress - FAO

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Transcript of Chapter 6-7: Abiotic and Biotic Stress - FAO