101
tuberisation (Haverkort and Harris 1987). However, highland farmers are at risk of
unpredictable rainfall and increasing temperatures caused by climate change and
variability that affect farm productivity under rain-fed conditions. Potato growing is
highly susceptible to precipitation variation and 575 mm is the minimum rainfall
required per cropping season to obtain reasonable yields of 20 t/ha. Erratic rainfall
in Kenya during the 2016–2017 drought reduced yields obtained by seed potato
multipliers by 56%, from 15 to 7 t/ha. This was after a reduction in rainfall from a
Table 9.1 Key characteristics of propagation material of potato and sweetpotato, as compared to
maize
Characteristics
Maize
Potato
Sweetpotato
g
Consumed plant
part
Seeds
Tubers
Roots
Most common
propagation
material
Seeds
Tubers
Vine cuttings
Multiplication
ratio
1:300
1:7.5–10
1:3 (a vine may yield 2 or 3
cuttings 30 cm long)
Bulkiness
20 kg/ha
2000 kg/ha
b
Approx. 666 kg/ha
depending on variety and
stage of wilting (33,300
cuttings of 25–30 cm)
Storability of
harvested seed
Up to 1 year
Up to 6 months
2–3 days
Seed cost (USD/
ha)
USD16 to
USD27
a
Up to 50–70% of the total
production cost
c
:
USD2,527/ha (Chile
d );
USD818/ha (Idaho
e
);
USD1090/ha (Peru
f
)
Highly variable. For
Tanzania: USD2 bundle of
300 vines (900 cuttings),
circa USD76/ha
Main pest and
diseases causing
seed
degeneration
Seed degeneration
is due to
contamination by
pollen from other
varieties
Potato virus X, potato virus
Y, potato leafroll virus,
Ralstonia, Rhizoctonia,
Pectobacterium,
Spongospora, Globodera,
Meloidogyne, Tecia,
Symmetrischema,
Phthorimaea, etc.
c
Viruses: a complex
sweetpotato chlorotic stunt
virus and sweetpotato
feathery mottle virus
transmitted by whitefly and
aphids. Weevils also
damage and are transmitted
through seed, namely
Cylas brunneus and C.
puncticollis
Adapted from Bentley et al. (2016)
a
USD0.80–USD1.00/kg for open-pollinated subsidized maize in Nigeria, USD1.33/kg for privatesector hybrid (Mele and Guéi 2011). Certified maize seed is sold for roughly the same price in
Peru, according to the INIA website www.inia.gob.pe/prod-servicios/semillas
b
Struik and Wiersema (1999)
c
Thomas-Sharma et al. (2016)
d
Ministerio de Agricultura de Chile (2013) 1 USD = 554 Chilean pesos
e
Patterson (2014)
f
Victor Suárez, personal communication. Varieties Canchán and Yungay in Julcán province, La
Libertad department in 2013. 1 USD = 2.75 Peruvian Sol
g
Kwame Ogero, personal communication
9 Climate Change and Seed Systems of Roots, Tubers and Bananas: The Cases…
tuberisation (Haverkort and Harris 1987). However, highland farmers are at risk of
unpredictable rainfall and increasing temperatures caused by climate change and
variability that affect farm productivity under rain-fed conditions. Potato growing is
highly susceptible to precipitation variation and 575 mm is the minimum rainfall
required per cropping season to obtain reasonable yields of 20 t/ha. Erratic rainfall
in Kenya during the 2016–2017 drought reduced yields obtained by seed potato
multipliers by 56%, from 15 to 7 t/ha. This was after a reduction in rainfall from a
Table 9.1 Key characteristics of propagation material of potato and sweetpotato, as compared to
maize
Characteristics
Maize
Potato
Sweetpotato
g
Consumed plant
part
Seeds
Tubers
Roots
Most common
propagation
material
Seeds
Tubers
Vine cuttings
Multiplication
ratio
1:300
1:7.5–10
1:3 (a vine may yield 2 or 3
cuttings 30 cm long)
Bulkiness
20 kg/ha
2000 kg/ha
b
Approx. 666 kg/ha
depending on variety and
stage of wilting (33,300
cuttings of 25–30 cm)
Storability of
harvested seed
Up to 1 year
Up to 6 months
2–3 days
Seed cost (USD/
ha)
USD16 to
USD27
a
Up to 50–70% of the total
production cost
c
:
USD2,527/ha (Chile
d );
USD818/ha (Idaho
e
);
USD1090/ha (Peru
f
)
Highly variable. For
Tanzania: USD2 bundle of
300 vines (900 cuttings),
circa USD76/ha
Main pest and
diseases causing
seed
degeneration
Seed degeneration
is due to
contamination by
pollen from other
varieties
Potato virus X, potato virus
Y, potato leafroll virus,
Ralstonia, Rhizoctonia,
Pectobacterium,
Spongospora, Globodera,
Meloidogyne, Tecia,
Symmetrischema,
Phthorimaea, etc.
c
Viruses: a complex
sweetpotato chlorotic stunt
virus and sweetpotato
feathery mottle virus
transmitted by whitefly and
aphids. Weevils also
damage and are transmitted
through seed, namely
Cylas brunneus and C.
puncticollis
Adapted from Bentley et al. (2016)
a
USD0.80–USD1.00/kg for open-pollinated subsidized maize in Nigeria, USD1.33/kg for privatesector hybrid (Mele and Guéi 2011). Certified maize seed is sold for roughly the same price in
Peru, according to the INIA website www.inia.gob.pe/prod-servicios/semillas
b
Struik and Wiersema (1999)
c
Thomas-Sharma et al. (2016)
d
Ministerio de Agricultura de Chile (2013) 1 USD = 554 Chilean pesos
e
Patterson (2014)
f
Victor Suárez, personal communication. Varieties Canchán and Yungay in Julcán province, La
Libertad department in 2013. 1 USD = 2.75 Peruvian Sol
g
Kwame Ogero, personal communication
9 Climate Change and Seed Systems of Roots, Tubers and Bananas: The Cases…